tag:blogger.com,1999:blog-48357525229182203192024-03-13T17:53:04.016-04:0052 Active Device Technologies - conocimientos.com.veActive Device Technologies. Semiconductor Diodes. Varactors. Schottky Diode Frequency Multipliers. Transit Time Microwave Devices. Bipolar Junction Transistors (BJTs). Heterostructure Bipolar Transistors (HBTs). Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs). Metal Semiconductor Field Effect Ransistors (MESFETs). High Electron Mobility Transistors (HEMTs). RF Power Transistors from Wide Bandgap Materials. Tubes Jerry C. Monolithic Microwave IC TechnologyTecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.comBlogger100125tag:blogger.com,1999:blog-4835752522918220319.post-28843032480274548842010-07-25T23:22:00.002-04:302010-07-27T16:29:06.286-04:30Nanowires Key to Future Transistors<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><br />
</div><div>A new generation of ultrasmall transistors and more powerful computer chips using tiny structures called semiconducting nanowires are closer to reality after a key discovery by researchers at IBM, Purdue University and the University of California at Los Angeles.</div><div><br />
</div><div style="text-align: center;"><br />
</div><div style="text-align: center;"><img height="200" src="http://www.sciencedaily.com/images/2009/11/091126173023-large.jpg" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="163" /></div><div style="text-align: center;"><i>Researchers are closer to using tiny devices called semiconducting nanowires to create a new generation of ultrasmall transistors and more powerful computer chips. The researchers have grown the nanowires with sharply defined layers of silicon and germanium, offering better transistor performance. As depicted in this illustration, tiny particles of a gold-aluminum alloy were alternately heated and cooled inside a vacuum chamber, and then silicon and germanium gases were alternately introduced. As the gold-aluminum bead absorbed the gases, it became "supersaturated" with silicon and germanium, causing them to precipitate and form wires. (Credit: Purdue University, Birck Nanotechnology Center/Seyet LLC)</i></div><div style="text-align: center;"><br />
</div><div>The researchers have learned how to create nanowires with layers of different materials that are sharply defined at the atomic level, which is a critical requirement for making efficient transistors out of the structures.</div><div><br />
</div><div>"Having sharply defined layers of materials enables you to improve and control the flow of electrons and to switch this flow on and off," said Eric Stach, an associate professor of materials engineering at Purdue.</div><div><br />
</div><div>Electronic devices are often made of "heterostructures," meaning they contain sharply defined layers of different semiconducting materials, such as silicon and germanium. Until now, however, researchers have been unable to produce nanowires with sharply defined silicon and germanium layers. Instead, this transition from one layer to the next has been too gradual for the devices to perform optimally as transistors.</div><div><br />
</div><div>The new findings point to a method for creating nanowire transistors.</div><div><br />
</div><div>The findings are detailed in a research paper appearing Nov. 27 in the journal Science. The paper was written by Purdue postdoctoral researcher Cheng-Yen Wen, Stach, IBM materials scientists Frances Ross, Jerry Tersoff and Mark Reuter at the Thomas J. Watson Research Center in Yorktown Heights, N.Y, and Suneel Kodambaka, an assistant professor at UCLA's Department of Materials Science and Engineering.</div><div><br />
</div><div>Whereas conventional transistors are made on flat, horizontal pieces of silicon, the silicon nanowires are "grown" vertically. Because of this vertical structure, they have a smaller footprint, which could make it possible to fit more transistors on an integrated circuit, or chip, Stach said.</div><div><br />
</div><div>"But first we need to learn how to manufacture nanowires to exacting standards before industry can start using them to produce transistors," he said.</div><div><br />
</div><div>Nanowires might enable engineers to solve a problem threatening to derail the electronics industry. New technologies will be needed for industry to maintain Moore's law, an unofficial rule stating that the number of transistors on a computer chip doubles about every 18 months, resulting in rapid progress in computers and telecommunications. </div><div><br />
</div><div>Doubling the number of devices that can fit on a computer chip translates into a similar increase in performance. However, it is becoming increasingly difficult to continue shrinking electronic devices made of conventional silicon-based semiconductors.</div><div><br />
</div><div>"In something like five to, at most, 10 years, silicon transistor dimensions will have been scaled to their limit," Stach said.</div><div>Transistors made of nanowires represent one potential way to continue the tradition of Moore's law.</div><div><br />
</div><div>The researchers used an instrument called a transmission electron microscope to observe the nanowire formation. Tiny particles of a gold-aluminum alloy were first heated and melted inside a vacuum chamber, and then silicon gas was introduced into the chamber. As the melted gold-aluminum bead absorbed the silicon, it became "supersaturated" with silicon, causing the silicon to precipitate and form wires. Each growing wire was topped with a liquid bead of gold-aluminum so that the structure resembled a mushroom.</div><div><br />
</div><div>Then, the researchers reduced the temperature inside the chamber enough to cause the gold-aluminum cap to solidify, allowing germanium to be deposited onto the silicon precisely and making it possible to create a heterostructure of silicon and germanium.</div><div><br />
</div><div>The cycle could be repeated, switching the gases from germanium to silicon as desired to make specific types of heterostructures, Stach said.</div><div><br />
</div><div>Having a heterostructure makes it possible to create a germanium "gate" in each transistor, which enables devices to switch on and off.</div><div><br />
</div><div>The work is based at IBM's Thomas J. Watson Research Center and Purdue's Birck Nanotechnology Center in the university's Discovery Park and is funded by the National Science Foundation through the NSF's Electronic and Photonic Materials Program in the Division of Materials Research.</div><div><br />
</div><div><div class="MsoNormal" style="line-height: 150%; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span lang="EN-US" style="font-family: Sylfaen, serif;">Freddy Vallenilla, EES SECC 2</span></div></div></span>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-81571735657634342972010-07-25T23:17:00.002-04:302010-07-27T16:28:48.353-04:30New 'FinFETs' Promising For Smaller Transistors, More Powerful Chips<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><br />
</div><div>Purdue University researchers are making progress in developing a new type of transistor that uses a finlike structure instead of the conventional flat design, possibly enabling engineers to create faster and more compact circuits and computer chips.</div><div><br />
</div><div style="text-align: center;"><img height="146" src="http://www.sciencedaily.com/images/2009/11/091110171746-large.jpg" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div style="text-align: center;"><span class="Apple-style-span" style="font-family: Arial, Helvetica, sans-serif; line-height: 15px;"><em>Researchers are making progress in developing new types of transistors, called finFETs, which use a finlike structure instead of the conventional flat design, possibly enabling engineers to create faster and more compact circuits and computer chips. The fins are made not of silicon, but from a material called indium-gallium-arsenide, as shown in this illustration. (Credit: Birck Nanotechnology Center, Purdue University)</em></span></div><div><br />
</div><div>The fins are made not of silicon, like conventional transistors, but from a material called indium-gallium-arsenide. Called finFETs, for fin field-effect-transistors, researchers from around the world have been working to perfect the devices as potential replacements for conventional transistors.</div><div><br />
</div><div>In work led by Peide Ye, an associate professor of electrical and computer engineering, the Purdue researchers are the first to create finFETs using a technology called atomic layer deposition. Because atomic layer deposition is commonly used in industry, the new finFET technique may represent a practical solution to the coming limits of conventional silicon transistors.</div><div><br />
</div><div>"We have just demonstrated the proof of concept here," Ye said.</div><div><br />
</div><div>Findings are detailed in three research papers being presented during the International Electron Devices Meeting on Dec. 7-9 in Baltimore. The work is led by doctoral student Yanqing Wu, who provided major contributions for two of the papers.</div><div><br />
</div><div>The finFETs might enable engineers to sidestep a problem threatening to derail the electronics industry. New technologies will be needed for industry to keep pace with Moore's law, an unofficial rule stating that the number of transistors on a computer chip doubles about every 18 months, resulting in rapid progress in computers and telecommunications. Doubling the number of devices that can fit on a computer chip translates into a similar increase in performance. However, it is becoming increasingly difficult to continue shrinking electronic devices made of conventional silicon-based semiconductors.</div><div><br />
</div><div>In addition to making smaller transistors possible, finFETs also might conduct electrons at least five times faster than conventional silicon transistors, called MOSFETs, or metal-oxide-semiconductor field-effect transistors.</div><div><br />
</div><div>"The potential increase in speed is very important," Ye said. "The finFETs could enable industry to not only create smaller devices, but also much faster computer processors."</div><div>Transistors contain critical components called gates, which enable the devices to switch on and off and to direct the flow of electrical current. In today's chips, the length of these gates is about 45 nanometers, or billionths of a meter.</div><div><br />
</div><div>The semiconductor industry plans to reduce the gate length to 22 nanometers by 2015. However, further size reductions and boosts in speed are likely not possible using silicon, meaning new designs and materials will be needed to continue progress.</div><div><br />
</div><div>Indium-gallium-arsenide is among several promising semiconductor alloys being studied to replace silicon. Such alloys are called III-V materials because they combine elements from the third and fifth groups of the periodical table.</div><div><br />
</div><div>Creating smaller transistors also will require finding a new type of insulating layer essential for the devices to switch off. As gate lengths are made smaller than 22 nanometers, the silicon dioxide insulator used in conventional transistors fails to perform properly and is said to "leak" electrical charge.</div><div><br />
</div><div>One potential solution to this leaking problem is to replace silicon dioxide with materials that have a higher insulating value, or "dielectric constant," such as hafnium dioxide or aluminum oxide.</div><div><br />
</div><div>The Purdue research team has done so, creating finFETs that incorporate the indium-gallium-arsenide fin with a so-called "high-k" insulator. Previous attempts to use indium-gallium-arsenide finFETs to make devices have failed because too much current leaks from the circuit.</div><div><br />
</div><div>The researchers are the first to "grow" hafnium dioxide onto finFETs made of a III-V material using atomic layer deposition. The approach could make it possible to create transistors using the thinnest insulating layers possible -- only a single atomic layer thick.</div><div><br />
</div><div>The finlike design is critical to preventing current leakage, in part because the vertical structure can be surrounded by an insulator, whereas a flat device has the insulator on one side only.</div><div><br />
</div><div>The work is funded by the National Science Foundation and the Semiconductor Research Consortium and is based at the Birck Nanotechnology Center in Purdue's Discovery Park.</div><div><br />
</div><div><br />
</div><div><div class="MsoNormal" style="line-height: 150%; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span lang="EN-US" style="font-family: Sylfaen, serif;">Freddy Vallenilla, EES SECC 2</span></div></div></span>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-86728366448718714312010-07-25T23:08:00.002-04:302010-07-27T16:28:29.677-04:30Breakthrough in 'Spintronics' Could Lead to Energy Efficient Chips<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><br />
</div><div>Scientists from the MESA Institute for Nanotechnology of the University of Twente and the FOM Foundation have succeeded in transferring magnetic information directly into a semiconductor. For the first time, this is achieved at room temperature. This breakthrough brings the development of a more energy efficient form of electronics, so-called 'spintronics' within reach.</div><div style="text-align: center;"><br />
</div><div style="text-align: center;"><img height="168" src="http://www.sciencedaily.com/images/2009/11/091127124519-large.jpg" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div style="text-align: center;">Silicon spin sandwich. (Credit: Image courtesy of University of Twente)</div><div><br />
</div><div>So far, information exchange between a magnetic material and a semiconductor was only possible at very low temperature. The successful demonstration of information exchange at room temperature is a pivotal step in the development of an alternative paradigm for electronics. The main advantage of this new 'spintronics' technology is the reduced power consumption: in present-day computer chips, excessive heat production is already a problem, and this will soon become a limiting factor.</div><div><br />
</div><div><b>Digital by nature</b></div><div>Unlike conventional electronics that employs the charge of the electron and its transport, spintronics exploits another important property of the electron, namely the 'spin'. The sense of rotation of an electron is represented by a spin that either points up or down. In magnetic materials, the spin orientation can be used to store a bit of information as a '1' or a '0'. The challenge is to transfer this spin information to a semiconductor, such that the information can be processed in new spin-based electronic components. These are expected to operate at lower power consumption, since computations such as reversing the electron spin, require less power than the usual transport of charge.</div><div><br />
</div><div><b>Only a few atomic layers thick</b></div><div>To achieve an efficient information exchange, the researchers insert an ultra thin -- less than one nanometer thick -- layer of aluminum oxide between the magnetic material and the semiconductor: this corresponds to only a few atomic layers. The thickness and quality of this layer are crucial. The information is transferred by applying an electric current across the oxide interface, thereby introducing a magnetization in the semiconductor, with a controllable magnitude and orientation.</div><div>Importantly, the method works for silicon: the prevalent electronic material for which highly advanced fabrication technology is available. The researchers found that the spin information can propagate into the silicon to a depth of several hundred nanometers. This is sufficient for the operation of nanoscale spintronic components, according to researcher Ron Jansen. Now the next step is: to built new electronic components and circuits and use these to manipulate spin information.</div><div>The spintronics research is performed by a team of researchers led by Ron Jansen at the MESA+ Institute for Nanotechnology, and is made possible by financial support from the Foundation FOM and a VIDI-grant received from the Netherlands Organization for Scientific Research (NWO).</div><div><br />
</div><div><div class="MsoNormal" style="line-height: 150%; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span lang="EN-US" style="font-family: Sylfaen, serif;">Freddy Vallenilla, EES SECC 2</span></div></div></span>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-78155539304648841542010-07-24T23:05:00.002-04:302010-07-25T10:29:46.820-04:30High electron mobility transistor<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><br />
</div><div>High electron mobility transistor (HEMT), also known as heterostructure FET (HFET) or modulation-doped FET (MODFET), is a field effect transistor incorporating a junction between two materials with different band gaps as the channel instead of a doped region, as is generally the case for MOSFET. A commonly used material combination is GaAs with AlGaAs, though there is wide variation, dependent on the application of the device. Devices incorporating more indium generally show better high-frequency performance, while in recent years, gallium nitride HEMTs have attracted attention due to their high-power performance.</div><div><br />
</div><div style="text-align: center;"><img src="http://upload.wikimedia.org/wikipedia/commons/thumb/9/92/HEMT-scheme-en.svg/350px-HEMT-scheme-en.svg.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div style="text-align: center;">Cross section of a GaAs/AlGaAs/InGaAs pHEMT</div><div><br />
</div><div>To allow conduction, semiconductors are doped with impurities which donate mobile electrons (or holes). However, these electrons are slowed down through collisions with the impurities (dopants) used to generate them in the first place. HEMTs avoid this through the use of high mobility electrons generated using the heterojunction of a highly-doped wide-bandgap n-type donor-supply layer (AlGaAs in our example) and a non-doped narrow-bandgap channel layer with no dopant impurities (GaAs in this case).</div><div><br />
</div><div>The electrons generated in the thin n-type AlGaAs layer drop completely into the GaAs layer to form a depleted AlGaAs layer, because the heterojunction created by different band-gap materials forms a quantum well (a steep canyon) in the conduction band on the GaAs side where the electrons can move quickly without colliding with any impurities because the GaAs layer is undoped, and from which they cannot escape. The effect of this is to create a very thin layer of highly mobile conducting electrons with very high concentration, giving the channel very low resistivity (or to put it another way, "high electron mobility"). This layer is called a two-dimensional electron gas. As with all the other types of FETs, a voltage applied to the gate alters the conductivity of this layer.</div><div><br />
</div><div>Ordinarily, the two different materials used for a heterojunction must have the same lattice constant (spacing between the atoms). As an analogy, imagine pushing together two plastic combs with a slightly different spacing. At regular intervals, you'll see two teeth clump together. In semiconductors, these discontinuities form deep-level traps, and greatly reduce device performance.</div><div><br />
</div><div style="text-align: center;"><img src="http://upload.wikimedia.org/wikipedia/commons/thumb/9/9e/HEMT-band_structure_scheme-en.svg/350px-HEMT-band_structure_scheme-en.svg.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div style="text-align: center;">Band structure in GaAs/AlGaAs heterojunction based HEMT</div><div><br />
</div><div>A HEMT where this rule is violated is called a pHEMT or pseudomorphic HEMT. This is achieved by using an extremely thin layer of one of the materials – so thin that the crystal lattice simply stretches to fit the other material. This technique allows the construction of transistors with larger bandgap differences than otherwise possible, giving them better performance.</div><div><br />
</div><div>Another way to use materials of different lattice constants is to place a buffer layer between them. This is done in the mHEMT or metamorphic HEMT, an advancement of the pHEMT. The buffer layer is made of AlInAs, with the indium concentration graded so that it can match the lattice constant of both the GaAs substrate and the GaInAs channel. This brings the advantage that practically any Indium concentration in the channel can be realized, so the devices can be optimized for different applications (low indium concentration provides low noise; high indium concentration gives high gain).</div><div><br />
</div><div>Applications are similar to those of MESFETs – microwave and millimeter wave communications, imaging, radar, and radio astronomy – any application where high gain and low noise at high frequencies are required. HEMTs have shown current gain to frequencies greater than 600 GHz and power gain to frequencies greater than 1 THz. (Heterojunction bipolar transistors were demonstrated at current gain frequencies over 600 GHz in April 2005.) Numerous companies worldwide develop and manufacture HEMT-based devices. These can be discrete transistors but are more usually in the form of a 'monolithic microwave integrated circuit' (MMIC). HEMTs are found in many types of equipment ranging from cellphones and DBS receivers to electronic warfare systems such as radar and for radio astronomy.</div><div><br />
</div><div>The invention of the HEMT is usually attributed to Takashi Mimura (三村 高志) (Fujitsu, Japan). However, Ray Dingle and his co-workers in Bell Laboratories also played an important role in the invention of the HEMT.</div><div><br />
</div><div><br />
</div><div><div class="MsoNormal" style="line-height: 150%; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span lang="EN-US" style="font-family: Sylfaen, serif;">Freddy Vallenilla, EES SECC 2</span></div></div></span>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-20108217017230748362010-07-24T22:55:00.002-04:302010-07-25T10:29:30.601-04:30InP/GaInAs Single and Double Heterostructure Bipolar Transistors<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><br />
</div><div>InP/GaInAs HBTs are of central importance to the development of modern lightwave communication systems such as 40 Gb/s optical communication systems because they are compatible for integration with 1.3-1.5µm optoelectronic components such as lasers and photodetectors. At present only a few companies like Hughes, TRW, and Lucent provide commercial products based on InP HBTs. InP/GaInAs HBTs are the fastest bipolar transistors ever fabricated, but they present a number of complications related to the low breakdown voltages achievable in the narrow bandgap GaInAs (0.75eV) collectors. Double heterostructure HBTs with a wide bandgap InP or InAlAs collector permit marked improvements in breakdown voltages but tend to cause a blocking effect of electrons flowing through the base and into the collector. The blocking effects can be alleviated by grading the collector/base junction alloy composition, and various schemes have been developed (binary or chirped superlattice grading; or analog compositional grading) but all are sensitive to the exact details of the grading scheme.</div><div><br />
</div><div style="text-align: right;"><img src="http://www.mwe.ee.ethz.ch/typo3temp/pics/7571385fec.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div style="text-align: center;"><br />
</div><div>The figure on the right shows the equilibrium energy band diagram for an abrupt junction double heterostructure InP/GaInAs bipolar transistor. Complex grading schemes are required to alleviate the collector current blocking effect.</div><div><br />
</div><div style="text-align: left;"><img src="http://www.mwe.ee.ethz.ch/typo3temp/pics/d63bbbfdd4.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div><br />
</div><div>We MWF also investigating InP/GaInAs DHBTs with an InP collector because InP displays higher peak and saturated electron drift velocities, a high breakdown field of ~480 MV/cm, and a high thermal conductivity which allows an efficient heat dissipation in power HBTs operated at high voltages. </div><div>A fully self-aligned wet etch process was developed with evaporated (rather than electroplated) airbridge interconnects. Relatively large area emitter devices (4x12 µm2) have resulted in current gain cutoff frequencies as high as fT=105GHz with a maximum oscillation frequency fmax=85GHz. Scaling of the emitter width to 1µm will result in fmax values beyond 200GHz.</div><div>Figure on the left shown a Scanning Electron Microscope image of a 100GHz fully self-aligned InP/GaInAs heterostructure bipolar transistor with a 750Å base and a 7000Å collector. The emitter is on top. Note the evaporated airbridge interconnects. The process is carried out with wet etches only: the resulting surfaces are damage-free, and large BVceo voltages of 11-12V are achieved.</div><div><br />
</div><div><b>InP/GaAsSb/InP Double Heterostructure Bipolar Transistors</b></div><div><br />
</div><div>We have developed InP/GaAsSb/InP DHBTs that overcome the collector blocking effect described above by engineering MOCVD-grown DHBTs in which the GaAsSb p-base conduction band edge sits above the InP conduction band edge: instead of being slowed down by a blocking/opposing field due a to a chemical potential gradient, electrons reaching the base/collector junction benefit from a ballistic injection launching ramp that injects them into the InP collector with a high velocity: it is the total integrated velocity across the collector layer that determines the collector transit time, and we believe the ballistic launcher will prove very helpful in the realization of high speed InP based DHBTs. Our first public report of InP/GaAsSb/InP DHBTs was given at the 1998 IEEE Device Research Conference held June 22-24, 1998 in Charlottesville, VA.</div><div><br />
</div><div style="text-align: right;"><img src="http://www.mwe.ee.ethz.ch/typo3temp/pics/720066924f.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div><br />
</div><div>The figure on the upper right shows the equilibrium energy band diagram for an abrupt junction double heterostructure InP/GaAsSb/InP bipolar transistors. Note the ballistic electron launcher at the abrupt base-collector junction. The conduction band discontinuity at the InP/GaAsSb interface was determined by sophisticated high-resolution FTIR photoluminescence measurements of the type II recombination at the interface. The conduction band offset is equal to 0.18eV.</div><div><br />
</div><div style="text-align: left;"><img src="http://www.mwe.ee.ethz.ch/typo3temp/pics/c656f47f39.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div><br />
</div><div><br />
</div><div style="text-align: left;">The figure on the left shows room temperature I-V characteristics for a small area InP/GaAsSb/InP DHBTs. BVceo = 6-8V for a 1500Å InP collector layer. The knee voltage is smaller than 0.2V, a great advantage over the usual 0.6V of conventional GaAs MESFETs/HEMTs and HBTs. The collector offset voltage is 12-15mV because of the complete symmetry of the E/B and B/C heterojunctions.</div><div>InP/GaAsSb DHBTs have previously been explored by two other groups (Bellcore / Rockwell), but SFU was the first to demonstrate very nearly ideal Gummel characteristics and record collector Vce offset voltages as low as (12-15mV). The base and collector current ideality factors nb and nc are equal to 1.0 in both normal and reverse operation. Cutoff frequencies as high as 75GHz were also achieved in non-optimized structures. We attribute the improved performance of our devices to the careful selection of the growth conditions by cross-correlating the results of AFM, XRD, FTIR-PL, and device measurements.</div><div><br />
</div><div>Such low offset voltages are very attractive for wireless communication systems because there is an urgent need to develop highly efficient low-voltage power amplifiers: in 1998, wireless handset systems have begun a transition to 3.6V supply voltages (with either a 3-cell NiCd or NiMH or a single cell Li+ battery configuration). Note that in the early 1990's the supply voltage for wireless phones was 7.2V (achieved with 6 NiCd cells)-- so many batteries made the handsets bulky and heavy, and the high power dissipation affected the component lifetime. The drive to low-voltage and high amplifier efficiencies is of course fueled by the consumer demand for small handyphones with long talk-times between recharge cycles. As a 3.6V battery pack discharges, its voltage can drop as low as 2.7-3.0V: the power amplifier must continue to perform well as the supply voltage drops toward its end voltage (when the battery is completely discharged). </div><div>The potential advantages of InP-based HBTs, and particularly those of InP/GaAsSb DHBTs, for wireless handset applications are made very clear by comparing the collector current turn-on characteristics of bipolar transistors for various material systems.</div><div><br />
</div><div style="text-align: right;"><img src="http://www.mwe.ee.ethz.ch/typo3temp/pics/09ec98f5af.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div><br />
</div><div>The figure on the right shows measured collector current densities in A/cm2 as a function of Vbe for InP/GaAsSb, InP/GaInAs, Si, and GaInP/GaAs transistors. Note how the voltage required for a certain collector current is much smaller in InP-based HBTs than for GaAs HBTs: this is largely a consequence of the smaller base material energy gaps. Base energy gaps: GaAs=1.42eV; Si=1.12eV; GaInAs=0.75eV; and GaAsSb=0.72eV. The saturation at high currents is due to probe and contact series resistance effects.</div><div><br />
</div><div><br />
</div><div><div class="MsoNormal" style="line-height: 150%; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span lang="EN-US" style="font-family: Sylfaen, serif;">Freddy Vallenilla, EES SECC 2</span></div></div></span>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-79311042380366812682010-07-24T22:37:00.002-04:302010-07-25T10:29:12.393-04:30Wide Band Gap Devices in Power Systems<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><br />
</div><div>Silicon carbide (SiC) is a wide band gap semiconductor material which is ideal for the production of power switching devices. It has excellent power handling and high-temperature operation capabilities. The defense industry has long been interested in the use of SiC technology for its high power applications, such as electric ships, high power weapon systems, hybrid electric vehicles, and More Electric Aircrafts (MEAs). Power electronics converter systems with SiC-based power semiconductor switching devices are lighter, more compact, and more efficient, making them ideal for high-voltage power electronic applications.</div><div><br />
</div><div>These highly desirable device improvements would also substantially trim the amount of undesirable power losses in electric motor drive power conversion applications. For example, SiC high-temperature electronic sensors and controls on an automobile engine will lead to better combustion monitoring and control, which would result in cleaner burning, more fuel efficient cars. SiC MOSFETs, Schottky diodes or PIN diodes, IGBT, Cascode modules, and JFETs are among the choices of the technologies, depending on maturity levels.</div><div><br />
</div><div style="text-align: center;"><img src="http://www.empf.org/empfasis/2006/jan06/images/wbgfig1.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div><br />
</div><div>The U.S. Navy's DD(X) next generation destroyer requires power control, distribution, and Integrated Power System (IPS) power conversion at multi-MW levels. The power conversion modules (PCMs) for use in the Integrated Fight Through Power (IFTP) of the IPS would benefit substantially from SiC technology. PCM-1 contains DC-to-DC converters with a required rating of at least 750kW. The transfer switch cabinet has a 5000 amp capacity rated DC switch with 1000VDC. The Ship Service Conversion Modules (SSCMs) in PCM-1 convert the DC input (1000VDC) to a lower DC voltage output (800VDC). Si IGBT modules with a 100KW power rating are currently in use. PCM-2 contains DC-AC inverters (Ship Service Invert Modules/SSIMs) with a required rating of at least of 500kW. PCM-4 consists of the hardware and software necessary to convert AC, three-phase, three-wire (the source neutral is grounded via high impedance at the source), 60Hz power from the propulsion bus to DC power. A PCM-4 consists of a transformer and rectifier to convert 4160VAC (3-phase, 60Hz) to 1000VDC.</div><div><br />
</div><div>The development of More Electric Aircraft (MEA) begins by addressing the need for generation and control of significantly increased on-board aircraft electric power. The present distributed controls and actuators for MEA flight control systems and surfaces are typically electrically-controlled but hydraulically-powered. Future systems should be controlled optically and powered electrically. Devices for generation and protection (circuit breakers) will range from 600 to 1000V and will require reliable devices at current levels up to 1000A. One of the key design requirements for new power generation will be the ability to provide high quality power generation at variable generator frequencies.</div><div><br />
</div><div>Replacement of constant frequency generators having variable frequency capability will eliminate the need for integrated drive subsystems (currently used to cancel out engine speed variations while providing constant generator speeds). Operability in the 300-400°C range with continuous operation will be required. Enabling technologies are: high quality power generation, optical control (optical bi-polar transistors), and smart actuator controls operating at higher voltages, to eliminate the cost and added weight of power conditioners. Since control will generally be provided by short, high-current pulses, the control devices will require both high voltages and high currents (though not as high as power generation and control). Typical ranges are from 600-1000 volts and from 5 to more than 600 amps. SiC diodes and transistors provide the primary enabling technology. The desired device types are SiC MOSFETs, with baseline comparison devices being Si IGBTs, which have been demonstrated above 1 kA current levels. Switch mode power conversion transistors are considered better than thyristors for these applications.</div><div><br />
</div><div>Solid-state systems, including flexible alternating current transmission systems (FACTS), use a series of silicon power transistors to control the flow of current. They have been used on a limited basis on the power grid; however, the use of SiC rather than silicon could greatly simplify FACTS, while significantly improving performance. For example, SiC could double the voltage per device, reducing the number of transistors needed in a series in each "electrical valve." This could increase operating frequency from about 500Hz to about 20kHz. Utilities could realize significant savings in auxiliary controls and reduce the size, cooling requirements, and maintenance of systems.</div><div><br />
</div><div>In the near future, one of the largest potential commercial applications for SiC Schottky rectifiers is in the continuous conduction mode (CCM) power factor correction (PFC) circuit. In traditional, off-line AC/DC power supplies used in computer and telecom applications, the AC input sees a large inductive (transformer) load, which causes the power factor to be substantially lower than 1. SiC Schottky diodes are suitable for applications that require blocking voltage under 3KV, and SiC PiN diodes are suitable for higher blocking voltage applications. The performance improvements include higher switching speed and lower switching loss. For example, in a test case power converter, replacing the best available 600V Si diodes with a 1500V SiC diode, resulted in an increase of power supply efficiency from 82 to 88 percent for switching at 186kHz, along with a reduction in EMI emissions.</div><div><br />
</div><div>SiC Schottky diodes have been considered as replacements for silicon PiN diodes in many high-frequency motor drive applications. A recent study by a market analysis group predicted that the global market for SiC Schottky diodes and transistors will increase from $13 million in 2004 to more than $53 million in 2009 – a compound annual growth rate of 32 percent. Just about any household or industrial electric motor in the world requires a power electronic drive which can be made smaller and more efficient with the use of SiC devices; however, SiC must become less expensive and more readily available before it can compete in the commercial industry of motors and motor drivers.</div><div><br />
</div><div>Other applications for SiC electronics are piezoelectric accelerometers. The traditional approach (used in 90 percent of high-temperature applications) is to move the electronics off of the sensor and down to an external charge amplifier, in a cooler location. This introduces significant noise to the signal. An alternate approach which could be used on some aircraft engine designs, is to use high-temperature electronics inside the sensor housing up to 210°C. SiC should increase this temperature limit to 370°C. The application of SiC high-temperature electronics would allow performance improvements to sensors that could not obtain such improvements otherwise.</div><div><br />
</div><div>SiC sensors have been tested on automotive applications with positive results. Both military and commercial aircrafts would gain significant enhancements to their performance. Crucial to realizing these new components is the ability to sufficiently amplify low-level sensor signals (vibration, temperature, pressure) to enable transmission over moderate distances. The availability of an operational amplifier (op-amp) functioning reliably at temperatures as high as 370°C would serve this purpose. It would also provide a fundamental building block for sensor manufacturers to design circuits that amplify low-level signals and signal the condition of the electrical output from pressure and temperature sensors operating at high temperatures. With the availability of high-temperature op-amps, A/D converters, and resistive and capacitive components, circuits could be designed that would read the bridge resistance output at the high-temperature strain gauge pressure sensor. These circuits would also perform temperature and pressure linearity compensation and signal amplification. Such a circuit would be a major step towards a high-temperature "smart" sensor.</div><div><br />
</div><div>Overall, the implementation of SiC devices in high power systems would provide significant improvements to system performance, reduce system size and power loss, and potentially lower the overall system cost. The challenges of implementing SiC devices are lack of high quality materials and lack of suitable high temperature packages. Over the past decade, the wide band gap semiconductor industry has been working aggressively to improve material quality, the device fabrication process, and device reliability, making impressive advances. The Department of Defense has also made significant investments to advance wide band gap technology. Currently, SiC Schottky diodes are available commercially from a few companies. SiC MOSFETs and PIN diodes have been demonstrated and are expected to further advance in the next 12 to 18 months.</div><div><br />
</div><div><br />
</div><div><div class="MsoNormal" style="line-height: 150%; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span lang="EN-US" style="font-family: Sylfaen, serif;">Freddy Vallenilla, EES SECC 2</span></div></div></span>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-86469002985701164682010-07-24T22:30:00.002-04:302010-07-25T10:27:44.697-04:30High Electron Mobility Transistors (HEMT)<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><br />
</div><div>The High Electron Mobility Transistor (HEMT) is a heterostructure field-effect transistor (FET).</div><div>Its principle is based on a heterojunction which consists of at least two different semiconducting materials brought into intimate contact. Because of the different band gaps and their relative alignment to each other, band discontinuities occur at the interface between the two semiconducting materials.</div><div><br />
</div><div style="text-align: center;"><img src="http://www.mwe.ee.ethz.ch/typo3temp/pics/f1854c8dd9.jpg" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div style="text-align: center;">Diagram of the band structures of two InAlAs and InGaAs at the equilibrium.</div><div style="text-align: center;"><br />
</div><div>These discontinuities are referred to as the conduction and valence band offsets ΔEc and ΔEv. By choosing proper materials and compositions thereof, the conduction band offset can form a triangular shaped potential well confining electrons in the horizontal direction. Within the well the electrons can only move in a two-dimensional plane parallel to the heterointerface and are therefore referred to as a two-dimentional electron gas (2DEG).</div><div>To determine the exact shape of the conduction and valence bands, the Schrödinger and Poisson equations must be solved self-consistently.</div><div><br />
</div><div style="text-align: center;"><img src="http://www.mwe.ee.ethz.ch/typo3temp/pics/693fb1a15f.jpg" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div style="text-align: center;">Semiconductors in contact at the equilibrium. A 2DEG is formed at the interface.</div><div><br />
</div><div><b><span class="Apple-style-span" style="font-size: large;">Indium Phosphide (InP) HEMT</span></b></div><div><b><span class="Apple-style-span" style="font-size: large;"><br />
</span></b></div><div style="text-align: center;"><b><span class="Apple-style-span" style="font-size: large;"><img height="110" src="http://www.mwe.ee.ethz.ch/typo3temp/pics/b7b2a205b9.jpg" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></span></b></div><div><br />
</div><div>Taking advantage of the fact that the 2DEG offers exceptional high carrier mobilities compared to bulk material, a typical InPHEMT has the following layer structure:</div><div>-Silicon δ-doping layer. Highly doped layer with only few atomic layers thickness. Located between the Schottky-Barrier and Spacer layer. Acting as a donor of charge arriers, it provides electrons to the channel. Since electrons tend to occupy the lowest allowed energy state, they drain into the potential well and form the confined 2DEG in the channel.</div><div>A high δ-doping level provides high electron densities in the channel and therefore results in high transconductances, current densities and cut-off frequencies.</div><div>-The Spacer layer assures the separation between the electrons and their positively charged Si-donors, reducing impurity scattering and hence enhancing electron mobility.</div><div>-A highly n-doped Cap layer helps minimize the contact resistance of the source and drain contacts. The cap also provides protection from oxidation for the sensitive InAlAs layer beneath.</div><div>-The Schottky-Barrier layer, in contrast to the Ohmic source and drain contacts, provides a so-called Shottky contact between gate-metal and semiconductor material with a rectifying characteristic. It prevents large currents from flowing trough the gate and limits tunneling to the channel.</div><div>-Channel properties have a major impact on the device performance. This is why InGaAs, with its excellent electron mobility properties at room and cryogenic temperatures, is the material of choice.</div><div>-The special T-shape of the gate helps minimize the gate resistance by enlarging the cross section while maintaining a small foot-print and thus a small gate length.</div><div><br />
</div><div style="text-align: center;"><img height="131" src="http://www.mwe.ee.ethz.ch/typo3temp/pics/949c3d4c8a.jpg" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div style="text-align: center;">Scanning Electron Micrograph of the cross-section of one of our HEMTs.</div><div><br />
</div><div><b>Applications</b></div><div><br />
</div><div>InP-HEMTs show excellent noise and gain performances at microwave frequencies. At cryogenic temperatures, these properties improve further. This predestines InP-HEMTs for receiver systems in and, which have the most stringent requirements for low noise and high sensitivity. Together with (Institut de Radio Astronomie Millimetrique), the Space Observatory, and (European Space Agency), the radio astronomy deep space communications IRAM Herschel ESA IFH/ETH has contributed to several projects involving cryogenically (~10K) cooled two- and three-stage low noise amplifiers (LNA). ETH "in-house" developed and processed HEMTs are being deployed in such missions.</div><div><br />
</div><div><span class="Apple-style-span" style="font-size: large;"><b>Gallium Nitride (GaN) HEMT</b></span></div><div><br />
</div><div style="text-align: center;"><img height="97" src="http://www.mwe.ee.ethz.ch/typo3temp/pics/0111295f45.jpg" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div>The second species of HEMTs in our group is based on GaN/AlGaN heterojunctions. Instead of using InP substrates the substrates are based on Sapphire (Al2O3 ) or Silicon Carbide (SiC). These semiconductors are both wide bandgap materials (3.4 eV and 3.3 eV compared to 1.3 eV for InP) and therefore have high electric breakdown fields, which enables applications at high supply voltages. Furthermore, this allows the material to withstand high operating temperatures and provides improved radiation hardness.</div><div>To achieve high currents and high frequency operation, high carrier mobilities and high saturation velocities are desirable. Typically, wide band gap semiconductors attain only relatively low mobilities but high saturation velocity values. Compared to the InP-HEMT structure the main differences are:</div><div>1) No doping in the AlGaN barrier layer is required. Built-in polarisation fields, due to spontaneous polarization and piezo-polarization help induce the 2DEG.</div><div>2) Higher 2DEG concentrations are achievable (above 10¹³/cm²) due to the very large conduction band discontinuity.</div><div></div><div><b>Applications</b></div><div><br />
</div><div>The direct bandgap of GaN and its alloys enables the material to be used for both optical and electronic applications. At 300 Kelvin the bandgap of GaN is 3.44 eV, which corresponds to a wavelength in the near ultra violet region of the optical spectrum. This enables the fabrication of high-power optical devices as LEDs and Lasers.</div><div>With respect to electronics, GaN is an excellent option for high-power/high-temperature microwave applications because of its high electric breakdown field and high electron saturation velocity (~1.5 x 10^7 cm/s). The former is a result of the wide bandgap (3.44 eV at room temperature) and enables the application of high supply voltages, which is one of the two requirements for high-power device performance. In addition, the wide bandgap allows the material to withstand high operating temperatures</div><div>(300°C - 500°C) enabling applications in many commercial areas not covered by other materials.</div><div><br />
</div><div><div class="MsoNormal" style="line-height: 150%; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span lang="EN-US" style="font-family: Sylfaen, serif;">Freddy Vallenilla, EES SECC 2</span></div></div></span>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-83281075074826305042010-07-24T21:10:00.002-04:302010-07-25T10:27:23.715-04:30Light-emitting diode (LED)<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><div><br />
</div><div>A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices, and are increasingly used for lighting. Introduced as a practical electronic component in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness.</div><div>The LED is based on the semiconductor diode. When a diode is forward biased (switched on), electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. An LED is usually small in area (less than 1 mm2), and integrated optical components are used to shape its radiation pattern and assist in reflection. LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. LEDs powerful enough for room lighting are relatively expensive and require more precise current and heat management than compact fluorescent lamp sources of comparable output.</div><div>They are used in applications as diverse as replacements for aviation lighting, automotive lighting (particularly indicators) and in traffic signals. The compact size of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are useful in advanced communications technology. Infrared LEDs are also used in the remote control units of many commercial products including televisions, DVD players, and other domestic appliances.</div><div><br />
</div><div style="text-align: center;"><img alt="RBG-LED.jpg" src="http://upload.wikimedia.org/wikipedia/commons/thumb/c/cb/RBG-LED.jpg/225px-RBG-LED.jpg" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div style="text-align: center;">Light-emitting diode</div><div style="text-align: center;"><br />
</div><div style="text-align: center;"><img alt="LED symbol.svg" src="http://upload.wikimedia.org/wikipedia/commons/thumb/e/e5/LED_symbol.svg/118px-LED_symbol.svg.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div style="text-align: center;">Electronic symbol</div><div><br />
</div><div><b><span class="Apple-style-span" style="font-size: large;">History</span></b></div><div><b><br />
</b></div><div><b>Discoveries and early devices</b></div><div><br />
</div><div>Electroluminescence was discovered in 1907 by the British experimenter H. J. Round of Marconi Labs, using a crystal of silicon carbide and a cat's-whisker detector. Russian Oleg Vladimirovich Losev independently reported on the creation of an LED in 1927. His research was distributed in Russian, German and British scientific journals, but no practical use was made of the discovery for several decades. Rubin Braunstein of the Radio Corporation of America reported on infrared emission from gallium arsenide (GaAs) and other semiconductor alloys in 1955. Braunstein observed infrared emission generated by simple diode structures using gallium antimonide (GaSb), GaAs, indium phosphide (InP), and silicon-germanium (SiGe) alloys at room temperature and at 77 kelvin.</div><div>In 1961, American experimenters Robert Biard and Gary Pittman working at Texas Instruments, found that GaAs emitted infrared radiation when electric current was applied and received the patent for the infrared LED.</div><div>The first practical visible-spectrum (red) LED was developed in 1962 by Nick Holonyak Jr., while working at General Electric Company. Holonyak is seen as the "father of the light-emitting diode". M. George Craford, a former graduate student of Holonyak, invented the first yellow LED and improved the brightness of red and red-orange LEDs by a factor of ten in 1972. In 1976, T.P. Pearsall created the first high-brightness, high efficiency LEDs for optical fiber telecommunications by inventing new semiconductor materials specifically adapted to optical fiber transmission wavelengths.</div><div>Up to 1968 visible and infrared LEDs were extremely costly, on the order of US $200 per unit, and so had little practical application. The Monsanto Company was the first organization to mass-produce visible LEDs, using gallium arsenide phosphide in 1968 to produce red LEDs suitable for indicators. Hewlett Packard (HP) introduced LEDs in 1968, initially using GaAsP supplied by Monsanto. The technology proved to have major applications for alphanumeric displays and was integrated into HP's early handheld calculators. In the 1970s commercially successful LED devices at under five cents each were produced by Fairchild Optoelectronics. These devices employed compound semiconductor chips fabricated with the planar process invented by Dr. Jean Hoerni at Fairchild Semiconductor. The combination of planar processing for chip fabrication and innovative packaging techniques enabled the team at Fairchild led by optoelectronics pioneer Thomas Brandt to achieve the necessary cost reductions. These techniques continue to be used by LED producers.</div><div><br />
</div><div><b>Practical use</b></div><div><br />
</div><div>he first commercial LEDs were commonly used as replacements for incandescent and neon indicator lamps, and in seven-segment displays, first in expensive equipment such as laboratory and electronics test equipment, then later in such appliances as TVs, radios, telephones, calculators, and even watches. These red LEDs were bright enough only for use as indicators, as the light output was not enough to illuminate an area. Readouts in calculators were so small that plastic lenses were built over each digit to make them legible. Later, other colors became widely available and also appeared in appliances and equipment. As the LED materials technology became more advanced, the light output was increased, while maintaining the efficiency and the reliability to an acceptable level. The invention and development of the high power white light LED led to use for illumination. Most LEDs were made in the very common 5 mm T1¾ and 3 mm T1 packages, but with increasing power output, it has become increasingly necessary to shed excess heat in order to maintain reliability, so more complex packages have been adapted for efficient heat dissipation. Packages for state-of-the-art high power LEDs bear little resemblance to early LEDs.</div><div><br />
</div><div><b>Continuing development</b></div><div><br />
</div><div>The first high-brightness blue LED was demonstrated by Shuji Nakamura of Nichia Corporation and was based on InGaN borrowing on critical developments in GaN nucleation on sapphire substrates and the demonstration of p-type doping of GaN which were developed by Isamu Akasaki and H. Amano in Nagoya. In 1995, Alberto Barbieri at the Cardiff University Laboratory (GB) investigated the efficiency and reliability of high-brightness LEDs and demonstrated a very impressive result by using a transparent contact made of indium tin oxide (ITO) on (AlGaInP/GaAs) LED. The existence of blue LEDs and high efficiency LEDs quickly led to the development of the first white LED, which employed a Y3Al5O12:Ce, or "YAG", phosphor coating to mix yellow (down-converted) light with blue to produce light that appears white. Nakamura was awarded the 2006 Millennium Technology Prize for his invention.</div><div>The development of LED technology has caused their efficiency and light output to increase exponentially, with a doubling occurring about every 36 months since the 1960s, in a way similar to Moore's law. The advances are generally attributed to the parallel development of other semiconductor technologies and advances in optics and material science. This trend is normally called Haitz's Law after Dr. Roland Haitz. </div><div>In February 2008, Bilkent university in Turkey reported 300 lumens of visible light per watt luminous efficacy (not per electrical watt) and warm light by using nanocrystals.</div><div>In January 2009, researchers from Cambridge University reported a process for growing gallium nitride (GaN) LEDs on silicon. Production costs could be reduced by 90% using six-inch silicon wafers instead of two-inch sapphire wafers. The team was led by Colin Humphreys.</div><div><br />
</div><div><b><span class="Apple-style-span" style="font-size: large;">Technology</span></b></div><div><br />
</div><div><b>Physics</b></div><div>Like a normal diode, the LED consists of a chip of semiconducting material doped with impurities to create a p-n junction. As in other diodes, current flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Charge-carriers—electrons and holes—flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon.</div><div>The wavelength of the light emitted, and therefore its color, depends on the band gap energy of the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes recombine by a non-radiative transition which produces no optical emission, because these are indirect band gap materials. The materials used for the LED have a direct band gap with energies corresponding to near-infrared, visible or near-ultraviolet light.</div><div>LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have made possible the production of devices with ever-shorter wavelengths, producing light in a variety of colors.</div><div>LEDs are usually built on an n-type substrate, with an electrode attached to the p-type layer deposited on its surface. P-type substrates, while less common, occur as well. Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate.</div><div>Most materials used for LED production have very high refractive indices. This means that much light will be reflected back into the material at the material/air surface interface. Therefore Light extraction in LEDs is an important aspect of LED production, subject to much research and development.</div><div><br />
</div><div style="text-align: center;"><img src="http://upload.wikimedia.org/wikipedia/commons/thumb/f/f9/LED%2C_5mm%2C_green_%28en%29.svg/300px-LED%2C_5mm%2C_green_%28en%29.svg.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div style="text-align: center;">Parts of an LED</div><div><br />
</div><div><b>Efficiency and operational parameters</b></div><div>Typical indicator LEDs are designed to operate with no more than 30–60 milliwatts [mW] of electrical power. Around 1999, Philips Lumileds introduced power LEDs capable of continuous use at one watt [W]. These LEDs used much larger semiconductor die sizes to handle the large power inputs. Also, the semiconductor dies were mounted onto metal slugs to allow for heat removal from the LED die.</div><div>One of the key advantages of LED-based lighting is its high efficiency, as measured by its light output per unit power input. White LEDs quickly matched and overtook the efficiency of standard incandescent lighting systems. In 2002, Lumileds made five-watt LEDs available with a luminous efficacy of 18–22 lumens per watt [lm/W]. For comparison, a conventional 60–100 W incandescent lightbulb produces around 15 lm/W, and standard fluorescent lights produce up to 100 lm/W. A recurring problem is that efficiency will fall dramatically for increased current. This effect is known as droop and effectively limits the light output of a given LED, increasing heating more than light output for increased current.</div><div>In September 2003, a new type of blue LED was demonstrated by the company Cree, Inc. to provide 24 mW at 20 milliamperes [mA]. This produced a commercially packaged white light giving 65 lm/W at 20 mA, becoming the brightest white LED commercially available at the time, and more than four times as efficient as standard incandescents. In 2006 they demonstrated a prototype with a record white LED luminous efficacy of 131 lm/W at 20 mA. Also, Seoul Semiconductor has plans for 135 lm/W by 2007 and 145 lm/W by 2008, which would be approaching an order of magnitude improvement over standard incandescents and better even than standard fluorescents. Nichia Corporation has developed a white LED with luminous efficacy of 150 lm/W at a forward current of 20 mA.</div><div>High-power (≥ 1 W) LEDs are necessary for practical general lighting applications. Typical operating currents for these devices begin at 350 mA.</div><div>Note that these efficiencies are for the LED chip only, held at low temperature in a lab. In a lighting application, operating at higher temperature and with drive circuit losses, efficiencies are much lower. United States Department of Energy (DOE) testing of commercial LED lamps designed to replace incandescent lamps or CFLs showed that average efficacy was still about 46 lm/W in 2009 (tested performance ranged from 17 lm/W to 79 lm/W).</div><div>Cree issued a press release on February 3, 2010 about a laboratory prototype LED achieving 208 lumens per watt at room temperature. The correlated color temperature was reported to be 4579 K</div><div><br />
</div><div style="text-align: center;"><img src="http://upload.wikimedia.org/wikipedia/commons/thumb/7/7c/PnJunction-LED-E.PNG/300px-PnJunction-LED-E.PNG" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div style="text-align: center;">The inner workings of an LED</div><div style="text-align: center;"><br />
</div><div><br />
</div><div style="text-align: center;"><img src="http://upload.wikimedia.org/wikipedia/commons/thumb/a/a5/Diode-IV-Curve.svg/300px-Diode-IV-Curve.svg.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div style="text-align: center;">I-V diagram for a diode an LED will begin to emit light when the on-voltage is exceeded. Typical on voltages are 2-3 Volt</div><div><br />
</div><div><b>Lifetime and failure</b></div><div><br />
</div><div>Solid state devices such as LEDs are subject to very limited wear and tear if operated at low currents and at low temperatures. Many of the LEDs produced in the 1970s and 1980s are still in service today. Typical lifetimes quoted are 25,000 to 100,000 hours but heat and current settings can extend or shorten this time significantly.</div><div>The most common symptom of LED (and diode laser) failure is the gradual lowering of light output and loss of efficiency. Sudden failures, although rare, can occur as well. Early red LEDs were notable for their short lifetime. With the development of high-power LEDs the devices are subjected to higher junction temperatures and higher current densities than traditional devices. This causes stress on the material and may cause early light output degradation. To quantitatively classify lifetime in a standardized manner it has been suggested to use the terms L75 and L50 which is the time it will take a given LED to reach 75% and 50% light output respectively.</div><div>Like other lighting devices, LED performance is temperature dependent. Most manufacturers' published ratings of LEDs are for an operating temperature of 25°C. LEDs used outdoors, such as traffic signals or in-pavement signal lights, and that are utilized in climates where the temperature within the luminaire gets very hot, could result in low signal intensities or even failure.</div><div>LEDs maintain consistent light output even in cold temperatures, unlike traditional lighting methods. Consequently, LED technology may be a good replacement in areas such as supermarket freezer lighting and will last longer than other technologies. Because LEDs do not generate as much heat as incandescent bulbs, they are an energy-efficient technology to use in such applications such as freezers. On the other hand, because they do not generate much heat, ice and snow may build up on the LED luminaire in colder climates. This has been a problem plaguing airport runway lighting, although some research has been done to try to develop heat sink technologies in order to transfer heat to alternative areas of the luminaire.</div><div><br />
</div><div><div><span class="Apple-style-span" style="font-size: large;">Colors and materials</span></div></div><div><br />
</div><div><div><table border="1" cellpadding="0" cellspacing="0" class="MsoNormalTable" style="background-attachment: initial; background-clip: initial; background-color: #f9f9f9; background-image: initial; background-origin: initial; border-bottom-style: none; border-collapse: collapse; border-color: initial; border-left-style: none; border-right-style: none; border-top-style: none; border-width: initial;"><tbody>
<tr><td style="background-attachment: initial; background-clip: initial; background-color: #f2f2f2; background-image: initial; background-origin: initial; border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: rgb(170, 170, 170); border-left-style: solid; border-left-width: 1pt; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: rgb(170, 170, 170); border-top-style: solid; border-top-width: 1pt; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"></td><td style="background-attachment: initial; background-clip: initial; background-color: #f2f2f2; background-image: initial; background-origin: initial; border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: rgb(170, 170, 170); border-top-style: solid; border-top-width: 1pt; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Color</span></div></td><td style="background-attachment: initial; background-clip: initial; background-color: #f2f2f2; background-image: initial; background-origin: initial; border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: rgb(170, 170, 170); border-top-style: solid; border-top-width: 1pt; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Wavelength (nm)</span></div></td><td style="background-attachment: initial; background-clip: initial; background-color: #f2f2f2; background-image: initial; background-origin: initial; border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: rgb(170, 170, 170); border-top-style: solid; border-top-width: 1pt; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Voltage (V)</span></div></td><td style="background-attachment: initial; background-clip: initial; background-color: #f2f2f2; background-image: initial; background-origin: initial; border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: rgb(170, 170, 170); border-top-style: solid; border-top-width: 1pt; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt; width: 121.25pt;" width="162"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Semiconductor Material</span></div></td></tr>
<tr><td style="background-attachment: initial; background-clip: initial; background-color: #200000; background-image: initial; background-origin: initial; border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: rgb(170, 170, 170); border-left-style: solid; border-left-width: 1pt; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Infrared</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">λ > 760</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">ΔV < 1.9</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt; width: 121.25pt;" width="162"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Gallium arsenide (GaAs)<br />
Aluminium gallium arsenide (AlGaAs)</span></div></td></tr>
<tr><td style="background-attachment: initial; background-clip: initial; background-color: red; background-image: initial; background-origin: initial; border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: rgb(170, 170, 170); border-left-style: solid; border-left-width: 1pt; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Red</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">610 < λ < 760</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">1.63 < ΔV < 2.03</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt; width: 121.25pt;" width="162"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Aluminium gallium arsenide (AlGaAs)<br />
Gallium arsenide phosphide (GaAsP)<br />
Aluminium gallium indium phosphide (AlGaInP)<br />
Gallium(III) phosphide (GaP)</span></div></td></tr>
<tr><td style="background-attachment: initial; background-clip: initial; background-color: #ff7f00; background-image: initial; background-origin: initial; border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: rgb(170, 170, 170); border-left-style: solid; border-left-width: 1pt; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Orange</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">590 < λ < 610</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">2.03 < ΔV < 2.10</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt; width: 121.25pt;" width="162"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Gallium arsenide phosphide (GaAsP)<br />
Aluminium gallium indium phosphide (AlGaInP)<br />
Gallium(III) phosphide (GaP)</span></div></td></tr>
<tr><td style="background-attachment: initial; background-clip: initial; background-color: yellow; background-image: initial; background-origin: initial; border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: rgb(170, 170, 170); border-left-style: solid; border-left-width: 1pt; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Yellow</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">570 < λ < 590</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">2.10 < ΔV < 2.18</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt; width: 121.25pt;" width="162"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Gallium arsenide phosphide (GaAsP)<br />
Aluminium gallium indium phosphide (AlGaInP)<br />
Gallium(III) phosphide (GaP)</span></div></td></tr>
<tr><td style="background-attachment: initial; background-clip: initial; background-color: lime; background-image: initial; background-origin: initial; border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: rgb(170, 170, 170); border-left-style: solid; border-left-width: 1pt; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Green</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">500 < λ < 570</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">1.9 < ΔV < 4.0</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt; width: 121.25pt;" width="162"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Indium gallium nitride (InGaN) / Gallium(III) nitride (GaN)<br />
Gallium(III) phosphide (GaP)<br />
Aluminium gallium indium phosphide (AlGaInP)<br />
Aluminium gallium phosphide (AlGaP)</span></div></td></tr>
<tr><td style="background-attachment: initial; background-clip: initial; background-color: blue; background-image: initial; background-origin: initial; border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: rgb(170, 170, 170); border-left-style: solid; border-left-width: 1pt; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Blue</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">450 < λ < 500</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">2.48 < ΔV < 3.7</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt; width: 121.25pt;" width="162"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Zinc selenide (ZnSe)<br />
Indium gallium nitride (InGaN)<br />
Silicon carbide (SiC) as substrate<br />
Silicon (Si) as substrate — (under development)</span></div></td></tr>
<tr><td style="background-attachment: initial; background-clip: initial; background-color: #8b00ff; background-image: initial; background-origin: initial; border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: rgb(170, 170, 170); border-left-style: solid; border-left-width: 1pt; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Violet</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">400 < λ < 450</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">2.76 < ΔV < 4.0</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt; width: 121.25pt;" width="162"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Indium gallium nitride (InGaN)</span></div></td></tr>
<tr><td style="background-attachment: initial; background-clip: initial; background-color: #bf00ff; background-image: initial; background-origin: initial; border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: rgb(170, 170, 170); border-left-style: solid; border-left-width: 1pt; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Purple</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">multiple types</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">2.48 < ΔV < 3.7</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt; width: 121.25pt;" width="162"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Dual blue/red LEDs,<br />
blue with red phosphor,<br />
or white with purple plastic</span></div></td></tr>
<tr><td style="background-attachment: initial; background-clip: initial; background-color: #200020; background-image: initial; background-origin: initial; border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: rgb(170, 170, 170); border-left-style: solid; border-left-width: 1pt; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Ultraviolet</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">λ < 400</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">3.1 < ΔV < 4.4</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt; width: 121.25pt;" width="162"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Diamond (235 nm)<br />
Boron nitride (215 nm)<br />
Aluminium nitride (AlN) (210 nm)<br />
Aluminium gallium nitride (AlGaN)<br />
Aluminium gallium indium nitride (AlGaInN)</span></div><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;"> (down to 210 nm)</span></div></td></tr>
<tr><td style="background-attachment: initial; background-clip: initial; background-color: white; background-image: initial; background-origin: initial; border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: rgb(170, 170, 170); border-left-style: solid; border-left-width: 1pt; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">White</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Broad spectrum</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt;"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">ΔV = 3.5</span></div></td><td style="border-bottom-color: rgb(170, 170, 170); border-bottom-style: solid; border-bottom-width: 1pt; border-left-color: initial; border-left-style: none; border-left-width: initial; border-right-color: rgb(170, 170, 170); border-right-style: solid; border-right-width: 1pt; border-top-color: initial; border-top-style: none; border-top-width: initial; font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 2.4pt; padding-left: 2.4pt; padding-right: 2.4pt; padding-top: 2.4pt; width: 121.25pt;" width="162"><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-size: 7pt; line-height: 10px;">Blue/UV diode with yellow phosphor </span></div></td></tr>
</tbody></table></div><div style="text-align: center;"><br />
</div></div><div><br />
</div><div><b><span class="Apple-style-span" style="font-size: large;">Types</span></b></div><div><br />
</div><div style="text-align: center;"><img height="70" src="http://upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Verschiedene_LEDs.jpg/750px-Verschiedene_LEDs.jpg" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div>LEDs are produced in a variety of shapes and sizes. The 5 mm cylindrical package (red, fifth from the left) is the most common, estimated at 80% of world production. The color of the plastic lens is often the same as the actual color of light emitted, but not always. For instance, purple plastic is often used for infrared LEDs, and most blue devices have clear housings. There are also LEDs in SMT packages, such as those found on blinkies and on cell phone keypads (not shown).</div><div><br />
</div><div><b>Miniature LEDs</b></div><div><br />
</div><div>These are mostly single-die LEDs used as indicators, and they come in various-sizes from 2 mm to 8 mm, through-hole and surface mount packages. They are usually simple in design, not requiring any separate cooling body.[67] Typical current ratings ranges from around 1 mA to above 20 mA. The small scale sets a natural upper boundary on power consumption due to heat caused by the high current density and need for heat sinking.</div><div><br />
</div><div style="text-align: center;"><img src="http://upload.wikimedia.org/wikipedia/commons/thumb/c/c0/LEDs_8_5_3mm.JPG/220px-LEDs_8_5_3mm.JPG" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div style="text-align: center;">Different sized LEDs. 8 mm, 5 mm and 3 mm, with a wooden match-stick for scale.</div><div><br />
</div><div><b>High power LEDs</b></div><div><br />
</div><div>High power LEDs (HPLED) can be driven at currents from hundreds of mA to more than an ampere, compared with the tens of mA for other LEDs. Some can produce over a thousand [68][69] lumens. Since overheating is destructive, the HPLEDs must be mounted on a heat sink to allow for heat dissipation. If the heat from a HPLED is not removed, the device will burn out in seconds. A single HPLED can often replace an incandescent bulb in a torch, or be set in an array to form a powerful LED lamp.</div><div>Some well-known HPLEDs in this category are the Lumileds Rebel Led, Osram Opto Semiconductors Golden Dragon and Cree X-lamp. As of September 2009 some HPLEDs manufactured by Cree Inc. now exceed 105 lm/W [70] (e.g. the XLamp XP-G LED chip emitting Cool White light) and are being sold in lamps intended to replace incandescent, halogen, and even fluorescent style lights as LEDs become more cost competitive.</div><div>LEDs have been developed by Seoul Semiconductor that can operate on AC power without the need for a DC converter. For each half cycle part of the LED emits light and part is dark, and this is reversed during the next half cycle. The efficacy of this type of HPLED is typically 40 lm/W.[71] A large number of LED elements in series may be able to operate directly from line voltage. In 2009 Seoul Semiconductor released a high DC voltage capable of being driven from AC power with a simple controlling circuit. The low power dissipation of these LEDs affords them more flexibility than the original AC LED design.</div><div style="text-align: center;"><br />
</div><div style="text-align: center;"><img src="http://upload.wikimedia.org/wikipedia/commons/thumb/0/09/2007-07-24_High-power_light_emiting_diodes_%28Luxeon%2C_Lumiled%29.jpg/200px-2007-07-24_High-power_light_emiting_diodes_%28Luxeon%2C_Lumiled%29.jpg" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div style="text-align: center;">High-power light emiting diodes </div><div><br />
</div><div><b>Mid-range LEDs</b></div><div><br />
</div><div>Medium power LEDs are often through-hole mounted and used when an output of a few lumen is needed. They sometimes have the diode mounted to four leads (two cathode leads, two anode leads) for better heat conduction and carry an integrated lens. An example of this is the Superflux package, from Philips Lumileds. These LEDs are most commonly used in light panels, emergency lighting and automotive tail-lights. Due to the larger amount of metal in the LED, they are able to handle higher currents (around 100 mA). The higher current allows for the higher light output required for tail-lights and emergency lighting.</div><div><br />
</div><div><b>Application-specific variations</b></div><div><br />
</div><div>Flashing LEDs are used as attention seeking indicators without requiring external electronics. Flashing LEDs resemble standard LEDs but they contain an integrated multivibrator circuit which causes the LED to flash with a typical period of one second. In diffused lens LEDs this is visible as a small black dot. Most flashing LEDs emit light of a single color, but more sophisticated devices can flash between multiple colors and even fade through a color sequence using RGB color mixing.</div><div>Bi-color LEDs are actually two different LEDs in one case. They consist of two dies connected to the same two leads antiparallel to each other. Current flow in one direction produces one color, and current in the opposite direction produces the other color. Alternating the two colors with sufficient frequency causes the appearance of a blended third color. For example, a red/green LED operated in this fashion will color blend to produce a yellow appearance.</div><div>Tri-color LEDs are two LEDs in one case, but the two LEDs are connected to separate leads so that the two LEDs can be controlled independently and lit simultaneously. A three-lead arrangement is typical with one common lead (anode or cathode).</div><div>RGB LEDs contain red, green and blue emitters, generally using a four-wire connection with one common lead (anode or cathode). These LEDs can have either common positive or common negative leads. Others however, have only two leads (positive and negative) and have a built in tiny electronic control unit.</div><div>Alphanumeric LED displays are available in seven-segment and starburst format. Seven-segment displays handle all numbers and a limited set of letters. Starburst displays can display all letters. Seven-segment LED displays were in widespread use in the 1970s and 1980s, but increasing use of liquid crystal displays, with their lower power consumption and greater display flexibility, has reduced the popularity of numeric and alphanumeric LED displays.</div><div><br />
</div><div><span class="Apple-style-span" style="font-size: large;"><b>Considerations for use</b></span></div><div><br />
</div><div><b>Power sources</b></div><div><br />
</div><div>The current/voltage characteristic of an LED is similar to other diodes, in that the current is dependent exponentially on the voltage (see Shockley diode equation). This means that a small change in voltage can lead to a large change in current. If the maximum voltage rating is exceeded by a small amount the current rating may be exceeded by a large amount, potentially damaging or destroying the LED. The typical solution is therefore to use constant current power supplies, or driving the LED at a voltage much below the maximum rating. Since most household power sources (batteries, mains) are not constant current sources, most LED fixtures must include a power converter. However, the I/V curve of nitride-based LEDs is quite steep above the knee and gives an If of a few milliamperes at a Vf of 3 V, making it possible to power a nitride-based LED from a 3 V battery such as a coin cell without the need for a current limiting resistor.</div><div><br />
</div><div><b>Electrical polarity</b></div><div><br />
</div><div>As with all diodes, current flows easily from p-type to n-type material. However, no current flows and no light is produced if a small voltage is applied in the reverse direction. If the reverse voltage becomes large enough to exceed the breakdown voltage, a large current flows and the LED may be damaged. If the reverse current is sufficiently limited to avoid damage, the reverse-conducting LED is a useful noise diode.</div><div><br />
</div><div><b>Safety</b></div><div><br />
</div><div>The vast majority of devices containing LEDs are "safe under all conditions of normal use", and so are classified as "Class 1 LED product"/"LED Klasse 1". At present, only a few LEDs—extremely bright LEDs that also have a tightly focused viewing angle of 8° or less—could, in theory, cause temporary blindness, and so are classified as "Class 2". In general, laser safety regulations—and the "Class 1", "Class 2", etc. system—also apply to LEDs.</div><div><br />
</div><div><b>Advantages</b></div><div><br />
</div><div>-Efficiency: LEDs produce more light per watt than incandescent bulbs.[75] Their efficiency is not affected by shape and size, unlike Fluorescent light bulbs or tubes.</div><div>-Color: LEDs can emit light of an intended color without the use of the color filters that traditional lighting methods require. This is more efficient and can lower initial costs.</div><div>-Size: LEDs can be very small (smaller than 2 mm2) and are easily populated onto printed circuit boards.</div><div>-On/Off time: LEDs light up very quickly. A typical red indicator LED will achieve full brightness in under a microsecond. LEDs used in communications devices can have even faster response times.</div><div>-Cycling: LEDs are ideal for use in applications that are subject to frequent on-off cycling, unlike fluorescent lamps that burn out more quickly when cycled frequently, or HID lamps that require a long time before restarting.</div><div>-Dimming: LEDs can very easily be dimmed either by pulse-width modulation or lowering the forward current.</div><div>-Cool light: In contrast to most light sources, LEDs radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics. Wasted energy is dispersed as heat through the base of the LED.</div><div>-Slow failure: LEDs mostly fail by dimming over time, rather than the abrupt burn-out of incandescent bulbs.</div><div>-Lifetime: LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000 hours of useful life, though time to complete failure may be longer. Fluorescent tubes typically are rated at about 10,000 to 15,000 hours, depending partly on the conditions of use, and incandescent light bulbs at 1,000–2,000 hours.</div><div>-Shock resistance: LEDs, being solid state components, are difficult to damage with external shock, unlike fluorescent and incandescent bulbs which are fragile.</div><div>-Focus: The solid package of the LED can be designed to focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner.</div><div>-Toxicity: LEDs do not contain mercury, unlike fluorescent lamps.</div><div><br />
</div><div><b>Disadvantages</b></div><div><br />
</div><div>-Some Fluorescent lamps can be more efficient.</div><div>-High initial price: LEDs are currently more expensive, price per lumen, on an initial capital cost basis, than most conventional lighting technologies. The additional expense partially stems from the relatively low lumen output and the drive circuitry and power supplies needed.</div><div>-Temperature dependence: LED performance largely depends on the ambient temperature of the operating environment. Over-driving the LED in high ambient temperatures may result in overheating of the LED package, eventually leading to device failure. Adequate heat-sinking is required to maintain long life. This is especially important when considering automotive, medical, and military applications where the device must operate over a large range of temperatures, and is required to have a low failure rate.</div><div>-Voltage sensitivity: LEDs must be supplied with the voltage above the threshold and a current below the rating. This can involve series resistors or current-regulated power supplies.</div><div>-Light quality: Most cool-white LEDs have spectra that differ significantly from a black body radiator like the sun or an incandescent light. The spike at 460 nm and dip at 500 nm can cause the color of objects to be perceived differently under cool-white LED illumination than sunlight or incandescent sources, due to metamerism, red surfaces being rendered particularly badly by typical phosphor based cool-white LEDs. However, the color rendering properties of common fluorescent lamps are often inferior to what is now available in state-of-art white LEDs.</div><div>-Area light source: LEDs do not approximate a "point source" of light, but rather a lambertian distribution. So LEDs are difficult to use in applications requiring a spherical light field. LEDs are not capable of providing divergence below a few degrees. This is contrasted with lasers, which can produce beams with divergences of 0.2 degrees or less.</div><div>-Blue hazard: There is a concern that blue LEDs and cool-white LEDs are now capable of exceeding safe limits of the so-called blue-light hazard as defined in eye safety specifications such as ANSI/IESNA RP-27.1-05: Recommended Practice for Photobiological Safety for Lamp and Lamp Systems.</div><div>-Blue pollution: Because cool-white LEDs, emit proportionally more blue light than conventional outdoor light sources such as high-pressure sodium lamps, the strong wavelength dependence of Rayleigh scattering means that cool-white LEDs can cause more light pollution than other light sources. The International Dark-Sky Association discourages the use of white light sources with correlated color temperature above 3,000 K.</div><div><br />
</div><div><b>Applications</b></div><div><br />
</div><div>-Application of LEDs fall into four major categories:</div><div>-Visual signal application where the light goes more or less directly from the LED to the human eye, to convey a message or meaning.</div><div>-Illumination where LED light is reflected from object to give visual response of these objects.</div><div>-Generate light for measuring and interacting with processes that do not involve the human visual system.</div><div>-Narrow band light sensors where the LED is operated in a reverse-bias mode and is responsive to incident light instead of emitting light.</div></div><div><br />
</div><div><br />
</div><div><div class="MsoNormal" style="line-height: 150%; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span lang="EN-US" style="font-family: Sylfaen, serif;">Freddy Vallenilla, EES SECC 2</span></div></div><div><br />
</div><div><br />
</div></span>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-31017882014352997332010-07-24T19:29:00.002-04:302010-07-25T10:26:58.827-04:30PIN diode<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><br />
</div><div>A PiN diode is a diode with a wide, lightly doped 'near' intrinsic semiconductor region between a p-type semiconductor and an n-type semiconductor regions. The p-type and n-type regions are typically heavily doped because they are used for ohmic contacts.</div><div><br />
</div><div>The wide intrinsic region is in contrast to an ordinary PN diode. The wide intrinsic region makes the PIN diode an inferior rectifier (the normal function of a diode), but it makes the PIN diode suitable for attenuators, fast switches, photodetectors, and high voltage power electronics applications.</div><div><br />
</div><div style="text-align: center;"><img src="http://upload.wikimedia.org/wikipedia/commons/thumb/a/ab/Pin-Diode.svg/220px-Pin-Diode.svg.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div><br />
</div><div><b>Operation</b></div><div><br />
</div><div>A PiN diode operates under what is known as high-level injection. In other words, the intrinsic "i" region is flooded with charge carriers from the "p" and "n" regions. Its function can be likened to filling up a water bucket with a hole on the side. Once the water reaches the hole's level it will begin to pour out. Similarly, the diode will conduct current once the flooded electrons and holes reach an equilibrium point, where the number of electrons is equal to the number of holes in the intrinsic region. When the diode is forward biased, the injected carrier concentration is typically several orders of magnitudes higher than the intrinsic level carrier concentration. Due to this high level injection, which in turn is due to the depletion process, the electric field extends deeply (almost the entire length) into the region. This electric field helps in speeding up of the transport of charge carriers from p to n region, which results in faster operation of the diode, making it a suitable device for high frequency operations.</div><div><br />
</div><div><b>Characteristics</b></div><div><br />
</div><div>A PIN diode obeys the standard diode equation for low frequency signals. At higher frequencies, the diode looks like an almost perfect (very linear, even for large signals) resistor. There is a lot of stored charge in the intrinsic region. At low frequencies, the charge can be removed and the diode turns off. At higher frequencies, there is not enough time to remove the charge, so the diode never turns off. The PIN diode has a poor reverse recovery time.</div><div><br />
</div><div>The high-frequency resistance is inversely proportional to the DC bias current through the diode. A PIN diode, suitably biased, therefore acts as a variable resistor. This high-frequency resistance may vary over a wide range (from 0.1 ohm to 10 kΩ in some cases; the useful range is smaller, though).</div><div><br />
</div><div>The wide intrinsic region also means the diode will have a low capacitance when reverse biased.</div><div><br />
</div><div>In a PIN diode, the depletion region exists almost completely within the intrinsic region. This depletion region is much larger than in a PN diode, and almost constant-size, independent of the reverse bias applied to the diode. This increases the volume where electron-hole pairs can be generated by an incident photon. Some photodetector devices, such as PIN photodiodes and phototransistors (in which the base-collector junction is a PIN diode), use a PIN junction in their construction.</div><div><br />
</div><div>The diode design has some design tradeoffs. Increasing the dimensions of the intrinsic region (and its stored charge) allows the diode to look like a resistor at lower frequencies. It adversely affects the time needed to turn off the diode and its shunt capacitance. PIN diodes will be tailored for a particular use.</div><div><br />
</div><div><b>Applications</b></div><div><br />
</div><div>PIN diodes are useful as RF switches, attenuators, and photodetectors.</div><div><br />
</div><div><b>RF and Microwave Switches</b></div><div><br />
</div><div>Under zero or reverse bias, a PIN diode has a low capacitance. The low capacitance will not pass much of an RF signal. Under a forward bias of 1 mA, a typical PIN diode will have an RF resistance of about 1 ohm, making it a good RF conductor. Consequently, the PIN diode makes a good RF switch.</div><div><br />
</div><div>Although RF relays can be used as switches, they switch very slowly (on the order of 10 milliseconds). A PIN diode switch can switch much more quickly.</div><div><br />
</div><div>The capacitance of an off discrete PIN diode might be 1pF. At 320MHz, the reactance of 1pF is about 500 ohms. In a 50 ohm system, the off state attenuation would be about 20dB -- which may not be enough attenuation. In applications that need higher isolation, switches are cascaded to improve the isolation. Cascading three of the above switches would give 60dB of attenuation.</div><div><br />
</div><div>PIN diode switches are used not only for signal selection, but they are also used for component selection. For example, some low phase noise oscillators use PIN diodes to range switch inductors.</div><div><br />
</div><div style="text-align: center;"><img src="http://upload.wikimedia.org/wikipedia/commons/thumb/8/8a/Microwave_Switch.png/220px-Microwave_Switch.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div><br />
</div><div><b>RF and Microwave Variable Attenuators</b></div><div><br />
</div><div>By changing the bias current through a PIN diode, it's possible to quickly change the RF resistance.</div><div><br />
</div><div>At high frequencies, the PIN diode appears as a resistor whose resistance is an inverse function of its forward current. Consequently, PIN diode can be used in some variable attenuator designs as amplitude modulators or output leveling circuits.</div><div><br />
</div><div>PIN diodes might be used, for example, as the bridge and shunt resistors in a bridged-T attenuator.</div><div><br />
</div><div style="text-align: center;"><img src="http://upload.wikimedia.org/wikipedia/commons/thumb/8/87/General_Microwave_Modulator.png/220px-General_Microwave_Modulator.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div><br />
</div><div><b>Limiters</b></div><div><br />
</div><div>PIN diodes are sometimes used as input protection devices for high frequency test probes. If the input signal is within range, the PIN diode has little impact as a small capacitance. If the signal is large, then the PIN diode starts to conduct and becomes a resistor that shunts most of the signal to ground.</div><div><br />
</div><div><b>Photodetector and photovoltaic cell</b></div><div><br />
</div><div>The PIN photodiode was invented by Jun-ichi Nishizawa and his colleagues in 1950.</div><div><br />
</div><div>PIN photodiodes are used in fibre optic network cards and switches. As a photodetector, the PIN diode is reverse biased. Under reverse bias, the diode ordinarily does not conduct (save a small dark current or Is leakage). A photon entering the intrinsic region frees a carrier. The reverse bias field sweeps the carrier out of the region and creates a current. Some detectors can use avalanche multiplication.</div><div><br />
</div><div>The PIN photovoltaic cell works in the same mechanism. In this case, the advantage of using a PIN structure over conventional semiconductor junction is the better long wavelength response of the former. In case of long wavelength irradiation, photons penetrate deep into the cell. But only those electron-hole pairs generated in and near the depletion region contribute to current generation. The depletion region of a PIN structure extends across the intrinsic region, deep into the device. This wider depletion width enables electron-hole pair generation deep within the device. This increases the quantum efficiency of the cell.</div><div><br />
</div><div>Typically, amorphous silicon thin-film cells use PIN structures. On the other hand, CdTe cells use NIP structure, a variation of the PIN structure. In a NIP structure, an intrinsic CdTe layer is sandwiched by n-doped CdS and p-doped ZnTe. The photons are incident on the n-doped layer unlike a PIN diode.</div><div><br />
</div></span>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-24536532258127494192010-07-24T18:56:00.002-04:302010-07-25T10:26:37.189-04:30Varactor Temperature Compensation<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><br />
</div><div>The DS1851 is a dual 8-bit digital-to-analog converter (DAC) which also contains dual independent 40-byte look-up tables (LUTs) and an internal digital temperature sensor. Its original application was the temperature compensation of bias circuits used in laser (VCSEL) drivers. This application brief describes how to use this A/D converter to provide the same type of temperature compensation in varactor diodes, variable capacitors commonly used in RF circuits. </div><div><br />
</div><div>Varactor Characteristics</div><div><br />
</div><div>Varactors are diodes that exhibit large changes in capacitance when the reverse bias is varied. The capacitance of a varactor decreases as the reverse bias is increased. A capacitance change ratio of greater than 5 is not uncommon. See Figure 1 for a typical varactor voltage-capacitance characteristic.</div><div><br />
</div><div style="text-align: center;"><img alt="Figure 1. Typical varactor voltage-capacitance characteristic." height="118" src="http://www.maxim-ic.com/images/appnotes/1964/1964Fig01.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div style="text-align: center;">Figure 1. Typical varactor voltage-capacitance characteristic. </div><div><br />
</div><div>Being able to vary the capacitance with a control voltage is useful especially in radio frequency (RF) applications. Varactors can be used to tune systems for gain and phase alignment and they are also commonly used in voltage controlled oscillator (VCO) applications.</div><div><br />
</div><div>Varactors exhibit a large positive temperature coefficient. The temperature coefficient also varies with the applied reverse voltage. The temperature coefficient can vary between 100 PPM/°C [parts per million (PPM) per degree Celsius (C)] to over 1200 PPM/°C. See Figure 2 for a typical varactor capacitance temperature coefficient characteristic.</div><div><br />
</div><div style="text-align: center;"><img alt="Figure 2. Typical varactor capacitance temperature coefficient characteristic." height="122" src="http://www.maxim-ic.com/images/appnotes/1964/1964Fig02.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div style="text-align: center;">Figure 2. Typical varactor capacitance temperature coefficient characteristic. </div><div><br />
</div><div>In most closed applications, the large temperature coefficient that varactors exhibit is not of major concern but in open-loop systems where performance is critical, it may be necessary to adjust the reverse bias voltage to account for the capacitance drift over temperature. This application note describes how the DS1851 can be used to adjust the reverse bias voltage over temperature to maintain a constant varactor capacitance.</div><div>Using DS1851 to Compensate for Varactor Capacitance Drift with Temperature</div><div><br />
</div><div>The DS1851 is a dual 8-bit digital-to-analog converter (DAC) which also contains dual independent 40-byte lookup tables (LUT) and an internal digital temperature sensor. The temperature sensor points to each location in the LUT in 4°C increments over the temperature range from -40°C to +95°C. In this manner, the LUT can assign a unique value to each DAC at any temperature to match a particular temperature coefficient.</div><div><br />
</div><div>Figure 3 demonstrates how the DS1851 can be used to set the capacitance of varactor diodes and also compensate for the temperature coefficient. Since varactor diodes have a positive temperature coefficient and since the capacitance decreases with increasing reverse bias, the LUT in the DS1851 needs to be programmed with increasing values for higher temperatures and decreasing values for lower temperatures.</div><div><br />
</div><div>Each DAC adjacent step in the DS1851 corresponds to a 3906 PPM step either up or down. The DAC step rate to match the varactor temperature coefficient can be calculated from the following formula:</div><div>DAC Step Rate = 3906 PPM / [4°C x Varactor Temperature Coefficient (PPM/°C)]</div><div>As an example, if for a particular reverse bias setting the varactor has a 600 PPM/°C temperature coefficient, then the LUT needs to be programmed to increase and decrease the DAC steps about every 1.63 positions to match the varactor temperature coefficient. This could be implemented by programming 5 increasing/decreasing values over an 8-byte range (8 bytes / 5 bytes = 1.6).</div><div><br />
</div><div style="text-align: center;"><img alt="Figure 3. DS1851 varactor temperature compensation circuit." height="113" src="http://www.maxim-ic.com/images/appnotes/1964/1964Fig03.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div style="text-align: center;">Figure 3. DS1851 varactor temperature compensation circuit. </div><div style="text-align: center;"><br />
</div><div style="text-align: left;"><div class="MsoNormal" style="line-height: 150%; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span lang="EN-US" style="font-family: Sylfaen, serif;">Freddy Vallenilla, EES SECC 2</span></div></div></span>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-28049024094349353962010-07-24T18:05:00.001-04:302010-07-25T10:26:18.234-04:30New ‘super’ low noise pHEMT devices<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><br />
</div><div>MicroWave Technology Inc (MwT) of Fremont, CA, USA, a subsidiary of IXYS Corporation, has introduced a family of three AlGaAs/InGaAs based low noise pHEMT devices with operational frequency up to 38 GHz.</div><div><br />
</div><div>MwT's new devices (MwT-LN240, MwT-LN300 and MwT-LN600) are fabricated using a high reliability AlGaAs/InGaAs pHEMT (pseudomorphic High Electron Mobility Transistor) process with a nominal 0.15 micron gate length and gate widths of 240 um, 300 um, and 600 um, respectively. These devices are equally effective for wideband (e.g. 6-18 GHz or 18-26 GHz) and narrow band applications up to 38 GHz, says the firm.</div><div><br />
</div><div>With minimum noise figure of 0.5 dB at 12 GHz with 2.5V drain bias, these devices are suited for commercial wireless and military applications requiring very low noise figure and high associated gain. Applications include: broadband military EW and defense communications, wireless communication infrastructures, point-to-point microwave radios, space/high rel, instrumentation and medical equipment.</div><div><br />
</div><div>The new devices are also available in surface mount packages, such as the MwT-71. Furthermore, the complete noise models such as "gamma opt" and noise parameters over frequency range are available for these devices to aid circuit design simulations. An application note on active bias circuitry for setting and stabilizing the gate bias is also available.</div><div><br />
</div><div>As an application support vehicle, MwT has developed 11 to 13 GHz hybrid modules using an MwT-LN240 (a 240 micrometer device) with a noise figure as low as 0.7 dB. A 6 to 18 GHz balanced amplifier module using a pair of MwT-LN240 devices has achieved noise figure between 1.5 and 1.7 dB across the band.</div><div><br />
</div><div><br />
</div><div><div class="MsoNormal" style="line-height: 150%; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span lang="EN-US" style="font-family: Sylfaen, serif;">Freddy Vallenilla, EES SECC 2</span></div></div></span>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-16838419394203000432010-07-24T17:48:00.001-04:302010-07-25T10:26:02.065-04:30The Shockley Diode<div><span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div>Our exploration of thyristors begins with a device called the four-layer diode, also known as a PNPN diode, or a Shockley diode after its inventor, William Shockley. This is not to be confused with a Schottky diode, that two-layer metal-semiconductor device known for its high switching speed. A crude illustration of the Shockley diode, often seen in textbooks, is a four-layer sandwich of P-N-P-N semiconductor material, Figure below.</div><div><br />
</div><div style="text-align: center;"> <img src="http://sub.allaboutcircuits.com/images/03192.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div><br />
</div><div style="text-align: center;">Shockley or 4-layer diode</div><div><br />
</div><div>Unfortunately, this simple illustration does nothing to enlighten the viewer on how it works or why. Consider an alternative rendering of the device's construction in Figure below.</div><div><br />
</div><div style="text-align: center;"> <img src="http://sub.allaboutcircuits.com/images/03193.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div><br />
</div><div style="text-align: center;">Transistor equivalent of Shockley diode</div><div><br />
</div><div>Shown like this, it appears to be a set of interconnected bipolar transistors, one PNP and the other NPN. Drawn using standard schematic symbols, and respecting the layer doping concentrations not shown in the last image, the Shockley diode looks like this (Figure below)</div><div><br />
</div><div style="text-align: center;"> <img height="79" src="http://sub.allaboutcircuits.com/images/03194.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div style="text-align: center;">Shockley diode: physical diagram, equivalent schematic diagram, and schematic symbol.</div><div><br />
</div><div>Let's connect one of these devices to a source of variable voltage and see what happens: (Figure below)</div><div><br />
</div><div style="text-align: center;"> <img src="http://sub.allaboutcircuits.com/images/03195.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div><br />
</div><div style="text-align: center;">Powered Shockley diode equivalent circuit.</div><div><br />
</div><div>With no voltage applied, of course there will be no current. As voltage is initially increased, there will still be no current because neither transistor is able to turn on: both will be in cutoff mode. To understand why this is, consider what it takes to turn a bipolar junction transistor on: current through the base-emitter junction. As you can see in the diagram, base current through the lower transistor is controlled by the upper transistor, and the base current through the upper transistor is controlled by the lower transistor. In other words, neither transistor can turn on until the other transistor turns on. What we have here, in vernacular terms, is known as a Catch-22.</div><div><br />
</div><div>So how can a Shockley diode ever conduct current, if its constituent transistors stubbornly maintain themselves in a state of cutoff? The answer lies in the behavior of real transistors as opposed to ideal transistors. An ideal bipolar transistor will never conduct collector current if no base current flows, no matter how much or little voltage we apply between collector and emitter. Real transistors, on the other hand, have definite limits to how much collector-emitter voltage each can withstand before one breaks down and conduct. If two real transistors are connected in this fashion to form a Shockley diode, each one will conduct if sufficient voltage is applied by the battery between anode and cathode to cause one of them to break down. Once one transistor breaks down and begins to conduct, it will allow base current through the other transistor, causing it to turn on in a normal fashion, which then allows base current through the first transistor. The end result is that both transistors will be saturated, now keeping each other turned on instead of off.</div><div><br />
</div><div>So, we can force a Shockley diode to turn on by applying sufficient voltage between anode and cathode. As we have seen, this will inevitably cause one of the transistors to turn on, which then turns the other transistor on, ultimately "latching" both transistors on where each will tend to remain. But how do we now get the two transistors to turn off again? Even if the applied voltage is reduced to a point well below what it took to get the Shockley diode conducting, it will remain conducting because both transistors now have base current to maintain regular, controlled conduction. The answer to this is to reduce the applied voltage to a much lower point where too little current flows to maintain transistor bias, at which point one of the transistors will cutoff, which then halts base current through the other transistor, sealing both transistors in the "off" state as each one was before any voltage was applied at all.</div><div><br />
</div><div>If we graph this sequence of events and plot the results on an I/V graph, the hysteresis is evident. First, we will observe the circuit as the DC voltage source (battery) is set to zero voltage: (Figure below)</div><div style="text-align: center;"><img height="80" src="http://sub.allaboutcircuits.com/images/03196.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div></div><div><br />
</div><div style="text-align: center;">Zero applied voltage; zero current</div><div><br />
</div><div>Next, we will steadily increase the DC voltage. Current through the circuit is at or nearly at zero, as the breakdown limit has not been reached for either transistor: (Figure below)</div><div><br />
</div><div style="text-align: center;"> <img height="80" src="http://sub.allaboutcircuits.com/images/03197.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div style="text-align: center;">Some applied voltage; still no current</div><div><br />
</div><div>When the voltage breakdown limit of one transistor is reached, it will begin to conduct collector current even though no base current has gone through it yet. Normally, this sort of treatment would destroy a bipolar junction transistor, but the PNP junctions comprising a Shockley diode are engineered to take this kind of abuse, similar to the way a Zener diode is built to handle reverse breakdown without sustaining damage. For the sake of illustration I'll assume the lower transistor breaks down first, sending current through the base of the upper transistor: (Figure below)</div><div><br />
</div><div style="text-align: center;"> <img height="80" src="http://sub.allaboutcircuits.com/images/03198.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div style="text-align: center;">More voltage applied; lower transistor breaks down</div><div><br />
</div><div>As the upper transistor receives base current, it turns on as expected. This action allows the lower transistor to conduct normally, the two transistors "sealing" themselves in the "on" state. Full current is quickly seen in the circuit: (Figure below)</div><div><br />
</div><div style="text-align: center;"> <img height="80" src="http://sub.allaboutcircuits.com/images/03199.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div style="text-align: center;">Transistors are now fully conducting.</div><div><br />
</div><div>The positive feedback mentioned earlier in this chapter is clearly evident here. When one transistor breaks down, it allows current through the device structure. This current may be viewed as the "output" signal of the device. Once an output current is established, it works to hold both transistors in saturation, thus ensuring the continuation of a substantial output current. In other words, an output current "feeds back" positively to the input (transistor base current) to keep both transistors in the "on" state, thus reinforcing (or regenerating) itself.</div><div><br />
</div><div>With both transistors maintained in a state of saturation with the presence of ample base current, each will continue to conduct even if the applied voltage is greatly reduced from the breakdown level. The effect of positive feedback is to keep both transistors in a state of saturation despite the loss of input stimulus (the original, high voltage needed to break down one transistor and cause a base current through the other transistor): (Figure below)</div><div><br />
</div><div style="text-align: center;"> <img height="80" src="http://sub.allaboutcircuits.com/images/03200.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div style="text-align: center;">Current maintained even when voltage is reduced</div><div><br />
</div><div>If the DC voltage source is turned down too far, though, the circuit will eventually reach a point where there isn't enough current to sustain both transistors in saturation. As one transistor passes less and less collector current, it reduces the base current for the other transistor, thus reducing base current for the first transistor. The vicious cycle continues rapidly until both transistors fall into cutoff: (Figure below)</div><div><br />
</div><div style="text-align: center;"> <img height="80" src="http://sub.allaboutcircuits.com/images/03201.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div style="text-align: center;">If voltage drops too low, both transistors shut off.</div><div><br />
</div><div>Here, positive feedback is again at work: the fact that the cause/effect cycle between both transistors is "vicious" (a decrease in current through one works to decrease current through the other, further decreasing current through the first transistor) indicates a positive relationship between output (controlled current) and input (controlling current through the transistors' bases).</div><div><br />
</div><div>The resulting curve on the graph is classically hysteretic: as the input signal (voltage) is increased and decreased, the output (current) does not follow the same path going down as it did going up: (Figure below)</div><div><br />
</div><div style="text-align: center;"> <img src="http://sub.allaboutcircuits.com/images/03202.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div><br />
</div><div style="text-align: center;">Hysteretic curve</div><div><br />
</div><div>Put in simple terms, the Shockley diode tends to stay on once its turned on, and stay off once its turned off. No "in-between" or "active" mode in its operation: it is a purely on or off device, as are all thyristors.</div><div><br />
</div><div>A few special terms apply to Shockley diodes and all other thyristor devices built upon the Shockley diode foundation. First is the term used to describe its "on" state: latched. The word "latch" is reminiscent of a door lock mechanism, which tends to keep the door closed once it has been pushed shut. The term firing refers to the initiation of a latched state. To get a Shockley diode to latch, the applied voltage must be increased until breakover is attained. Though this action is best described as transistor breakdown, the term breakover is used instead because the result is a pair of transistors in mutual saturation rather than destruction of the transistor. A latched Shockley diode is re-set back into its nonconducting state by reducing current through it until low-current dropout occurs.</div><div><br />
</div><div>Note that Shockley diodes may be fired in a way other than breakover: excessive voltage rise, or dv/dt. If the applied voltage across the diode increases at a high rate of change, it may trigger. This is able to cause latching (turning on) of the diode due to inherent junction capacitances within the transistors. Capacitors, as you may recall, oppose changes in voltage by drawing or supplying current. If the applied voltage across a Shockley diode rises at too fast a rate, those tiny capacitances will draw enough current during that time to activate the transistor pair, turning them both on. Usually, this form of latching is undesirable, and can be minimized by filtering high-frequency (fast voltage rises) from the diode with series inductors and parallel resistor-capacitor networks called snubbers: (Figure below)</div><div><br />
</div><div style="text-align: center;"> <img height="120" src="http://sub.allaboutcircuits.com/images/03203.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div style="text-align: center;">Both the series inductor and parallel resistor-capacitor "snubber" circuit help minimize the Shockley diode's exposure to excessively rising voltage.</div><div><br />
</div><div>The voltage rise limit of a Shockley diode is referred to as the critical rate of voltage rise. Manufacturers usually provide this specification for the devices they sell.</div></span></div><div><br />
</div><div><br />
</div><div><div class="MsoNormal" style="line-height: 150%; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span lang="EN-US" style="font-family: Sylfaen, serif; font-size: 12pt; line-height: 150%;">Freddy Vallenilla, EES, SECC 2</span></div></div>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-82363548497843529582010-07-24T17:20:00.002-04:302010-07-25T10:25:41.472-04:30Power MOSFETs<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div>What are Power MOSFETs ?</div><div><br />
</div><div>Power MOSFETs (Metal-Oxide Semiconductor Field Effect Transistors) are three-terminal silicon devices that function by applying a signal to the gate that controls current conduction between source and drain. Their current conduction capabilities are up to several tens of amperes, with breakdown voltage ratings (BVDSS) of 10V to 1000V.</div><div><br />
</div><div>What type of power MOSFET is used in integrated circuits?</div><div><br />
</div><div>MOSFETs used in integrated circuits are lateral devices with gate, source and drain all on the top of the device, with current flow taking place in a path parallel to the surface. The Vertical Double diffused MOSFET (VDMOS) uses the device substrate as the drain terminal. MOSFETs used in integrated circuits exhibit a higher on-resistance than those of discrete MOSFETs.</div><div><br />
</div><div>What package styles are used for power MOSFETs?</div><div><br />
</div><div>MOSFETs are available in Small Outline IC (SOIC) packages for applications where space is at a premium. Larger through-hole TO-220, TO-247 and the surface mountable D2PAK or SMD-220 are also available. Newer package styles include chip scale devices and also the DirectFET™ and PolarPak™ packages.</div><div><br />
</div><div>What fabrication processes are used for power MOSFETs ?</div><div><br />
</div><div>The fabrication processes used to manufacture power MOSFETs are the same as those used in today's VLSI circuits, although the device geometry, voltage and current levels are significantly different. Discrete monolithic MOSFETs have tens or hundreds of thousands of individual cells paralleled together in order to reduce their on-resistance.</div><div><br />
</div><div>Is there an SiC power MOSFET?</div><div><br />
</div><div>Cree is the first to come up with a viable MOSFET. The ability to make these parts rests on the gate structure, which requires a physics and chemistry solution. The company still has some "tweaking" to do with the process, but they appear to be well ahead of the other companies that have ventured into this technology.</div><div><br />
</div><div>The commercial production of 1200 V SiC power MOSFETs is now feasible because of recent advances in substrate quality, improvements in epitaxy, optimized device design, advances made in increasing channel mobility with nitridation annealing, and optimization of device fabrication processes. SiC is a better power semiconductor than silicon (Si) because SiC has a much higher electric field breakdown capability (almost 10x), higher thermal conductivity, and higher temperature operation capability (wide electronic band gap).</div><div><br />
</div><div>SiC excels over Si as a semiconductor material in 600V and higher rated breakdown voltage devices. SiC Schottky diodes at 600V and 1200V ratings are commercially available today and are already accepted as the best solution for efficiency improvement in boost converter topologies as well as in solar inverters by substituting them for the previously-used Si PiN free-wheeling diodes that have significant switching losses</div><div><br />
</div><div>The SiC MOSFET being discussed here is a 1200V, 20A device from Cree that has a 100mW RDS(on) at a +15V gate-source voltage. Besides the inherent reduction in on-resistance, SiC also offers a substantially reduced on-resistance variation over operating temperature. From 25°C to 150°C, SiC variations are in the range of 20% versus 200% to 300% for Si. The SiC MOSFET die is capable of operation at junction temperatures greater than 200°C but for this particular example it is limited by its TO-247 plastic package to 150°C.</div><div><br />
</div><div>How does a power MOSFET turn on?</div><div><br />
</div><div>The gate turns the MOSFET on when its gate-to-source voltage is above a specific threshold. Typical gate thresholds range from 1 to 4 V. When a positive bias greater than the gate-to-source threshold voltage (VGS(th) ) is applied to the gate, a current flows between source and drain. For gate voltages less than VGS(th) the device remains in the off-state.</div><div><br />
</div><div>What circuit type is used to turn the power MOSFET on?</div><div><br />
</div><div>When power semiconductor switches first found wide use, discrete transistors, pulse transformers, opto-couplers, among other components were used to drive the power MOSFET on and off. Now, specially designed gate driver ICs are used in many applications. Fig. 5-1 shows the equivalent circuit of a gate driver driving a power MOSFET. This minimizes the drive requirements from a low power circuit, such as a microprocessor, and also acts as a buffer between the controlling signal and the power semiconductor switch. The gate driver supplies enough drive to ensure that the power switch turns on properly. Some gate drivers also have protection circuits to prevent failure of the power semiconductor switch and also its load.</div><div><br />
</div><div style="text-align: center;"><img height="172" src="http://powerelectronics.com/images/Fig5-1-0515.jpg" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div>Are there other power MOSFET technologies in general use ?</div><div><br />
</div><div>The trench MOSFET has replaced the planar device in many applications because it extends the cell density limit. Trench technology allows a higher cell density but is more difficult to manufacture than the planar device. Process refinements have yielded devices with steadily increasing density and lower on-resistance. TrenchFET devices have achieved on-resistance less than 1mW for a 25mm2 silicon die, exclusive of lead resistance.</div><div><br />
</div><div>Trench MOSFETs employs the same schematic configuration of the older planar MOSFETs. And, new Trench MOSFETs offer significant advantages over the older generation Trench MOSFETs and also some improvements over the older planar MOSFET technology.</div><div><br />
</div><div>Are there other power MOSFET technologies?</div><div><br />
</div><div>Among the other technologies are MDMesh . STMicroelectronics said that the improvement in RDS(ON) achieved with MDmesh V will significantly reduce losses in line-voltage PFC circuits and power supplies, which will in turn enable new generations of electronic products offering better energy ratings and smaller dimensions. This new technology should help designers with high efficiency targets and also save power.</div><div><br />
</div><div>MDmesh V achieves its RDS(ON) per area performance by improving the transistor drain structure to lower the drain-source voltage drop. This reduces the device's on-state losses while also maintaining low gate charge (Qg), enabling energy-efficient switching at high speeds and delivering a low RDS(ON) x Qg Figure of Merit (FOM). ST claims that the breakdown voltage of 650V is also higher than competing 600V devices, delivering a valuable safety margin for designers. A further advantage of ST's MDmesh V MOSFETs is a cleaner turn-off waveform, enabling easier gate control and simpler filtering due to reduced EMI.</div><div><br />
</div><div>STMicroelectronics' STripFET technology uses an optimized layout and updated manufacturing process to improve the gate charge, gate resistance and input capacitance characteristics. The low gate charge enables excellent switching behavior and the low gate resistance means fast transient response. The technology also offers an extremely low figure-of-merit, meaning reduced conduction and switching losses.</div><div><br />
</div><div>STMicroelectronics has introduced a new series of 30V surface-mount power transistors, achieving on-resistance as low as 2 mΩ (max) to increase the energy efficiency of products such as computers, telecom and networking equipment. The latest-generation STripFET VI DeepGATE family process has high equivalent cell density and said to be best RDS(ON) in relation to active chip size. This is around 20 per cent better than the previous generation and allows the use of small surface-mount power packages in switching regulators and DC-to-DC converters, the company said.</div><div><br />
</div><div>The technology also benefits from inherently low gate charge, which allows designers to use high switching frequencies and thereby specify smaller passive components such as inductors and capacitors.</div><div><br />
</div><div>Infineon has developed CoolMOS™ technology for high voltage Power MOSFETs that reduces the RDS(ON) area product by a factor of five for 600V transistors. It has redefined the dependence of RDS(ON) on the breakdown voltage. The more than square-law dependence in the case of a standard MOSFET has been broken and a linear voltage dependence achieved. It is said that this opens the way to new fields of application even without avalanche operation. System miniaturization, higher switching frequencies, lower circuit parasitics, higher efficiency, reduced system costs are pointing the way towards future developments. It has also set new benchmarks for device capacitances. Due to chip shrink and novel internal structure, the technology shows a very small input capacitance as well as a strongly nonlinear output capacitance. The drastically lower gate charge facilitates and reduces the cost of controllability, and the smaller feedback capacitance reduces dynamic losses. This technology, improves the minimum RDS(ON) values in the 600 to 1000 V operating range.</div><div><br />
</div><div>What package types are used with power MOSFETs?</div><div><br />
</div><div>Devices with breakdown voltage ratings of 55V-60V and gate-threshold voltages of 2 to 3V are used mainly in through-hole packages such as TO-220, TO-247 or the surface mounted D2PAK (SMD220). These through-hole packages have very low thermal resistance. Despite their higher thermal resistances, more surface-mount SOIC packages are finding their way into applications due to the continuous reduction in on-resistance of power MOSFETs. SOIC packages save space and simplify system assembly. The newest generation of power MOSFETs use chip scale and ball grid array packages for low voltage power MOSFETs.</div><div><br />
</div><div>The International Rectifier DirectFET power package is surface-mount power MOSFET packaging technology designed for efficient topside cooling in a SO-8 footprint. In combination with improved bottom-side cooling, the new package can be cooled on both sides to cut part count by up to 60%, and board space by as much as 50% compared to devices in standard or enhanced SO-8 packages. This effectively doubles current density (A/in2) at a lower total system cost. The DirectFET MOSFET family offerings match 20V and 30V synchronous buck converter MOSFET chipsets, followed by the addition at 30V targeted for high frequency operation. The DirectFET MOSFET family is also available in three different can sizes.</div><div><br />
</div><div>Vishay's PolarPAK® is a thermally enhanced package that facilitates MOSFET heat removal from an exposed top metal lead-frame connected to a drain surface in addition to a source lead-frame connected to a PCB. PolarPAK was specifically designed for easy handling and mounting onto the PCB with high-speed assembly equipment and thus to enable high assembly yields in mass-volume production. PolarPAK power MOSFETs have the same footprint dimensions of the standard SO-8, dissipate 1 °C/W from their top surface and 1 °C/W from their bottom surface. This provides a dual heat dissipation path that gives the devices twice the current density of the standard SO-8. With its improved junction-to-ambient thermal impedance, a PolarPAK power MOSFET can either handle more power or operate with a lower junction temperature. A lower junction temperature means a lower RDS(ON), which in turn means higher efficiency. A reduction in junction temperature of just 20 °C can also result in a 2.5 times increase in lifetime reliability.</div><div><br />
</div><div>What is the DrMOS power IC?</div><div><br />
</div><div>Intel's November 2004 DrMOS specification identified a multi-chip module consisting of a gate driver and power MOSFET. A major advantage of using this module (Fig 5-2) is that the individual MOSFET's performance characteristics can be optimized, whereas monolithic MOSFETs produce higher on-resistance. Although the component cost of a multi-chip module may be higher than a monolithic part. The designer must view the cost from a system viewpoint. That is, space is saved, potential noise problems are minimized, and fewer components reduce production time and cost. Here, the multi-chip approach is superior to use of a monolithic part.</div><div><br />
</div><div style="text-align: center;"><img height="136" src="http://powerelectronics.com/images/Fig5-3-0515.jpg" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div>Unlike discrete solutions whose parasitic elements combined with board layout significantly reduce system efficiency, the DRMOS module is designed to both thermally and electrically minimize parasitic effects and improve overall system efficiency. In operation, the high-side MOSFET is optimized for fast switching while the low-side device is optimized for low RDS(on). This arrangement ideally accommodates the low-duty-cycle switching requirements needed to convert the 12V bus to supply the processor core with 1.0V to 1.2V at up to 30A.</div><div><br />
</div><div>What are the necessary characteristics for power MOSFETs used in synchronous rectifiers?</div><div><br />
</div><div>Fig. 5-3 shows a simplified synchronous rectifier circuit. Typical synchronous rectifiers consist of high-side and low-side MOSFETs, which require different characteristics for an optimum design. Generally, the best high side MOSFET is one with the lowest Qswitch × RDS(ON) figure-of-merit. Qswitch is defined as the post gate threshold portion of the gate-to-source charge plus the gate-to-drain charge (Qgs2 + Qgd). In contrast, the best high side MOSFET must exhibit very low RDS(ON) coupled with good Cdv/dt immunity.</div><div><br />
</div><div>Low voltage (<20V) p-channel power MOSFETs are used as power management switches in cell phones and PDAs. Increasingly, n-channel devices are being used as switching or synchronous FETs in step-up or step-down regulators in these applications. Minimization of (RDS(on) x Active area) for power management switches and (RDS(on) × Qgd) for the dc-dc converters are important considerations in new product developments for this market. Defining RDS(on) max. @ Vgs of 4.5V and Qgd typ @ Vds of 15V, gate charge optimized planar MOSFETs and third generation trench devices with figures of merit of below 100 mΩ×nC have been developed.</div><div><br />
</div><div>How do you compare MOSFETs and BJTs?</div><div><br />
</div><div>Power MOSFETs are capable of operating at very high frequencies compared with Bipolar Junction Transistors (BJTs) whose switching speed is much slower than for a power MOSFET of similar size and voltage rating. Typical rise and fall times of power MOSFETs are of the order of several nanoseconds which is two orders of magnitude faster than bipolar devices of similar voltage rating and active area. BJTs are limited to frequencies of less than 100kHz whereas power MOSFETs can operate up to 1MHz before switching losses become unacceptably high. Recent advances in the design and processing of MOSFETs are pushing this frequency limit higher.</div><div><br />
</div><div>Power MOSFETs are voltage controlled devices with simple drive circuitry requirements. Power BJTs on the other hand are current controlled devices requiring large base drive currents to keep the device in the ON state. Power MOSFETs have been replacing power BJTs in power application due to faster switching capability and ease of drive, despite the very advanced state of manufacturability and lower costs of BJTs.</div><div><br />
</div><div>BJTs suffer from thermal runaway. The forward voltage drop of a BJT decreases with increasing temperature potentially leading to destruction. This is of special significance when several devices are paralleled in order to reduce forward voltage drop. Power MOSFETs can be paralleled easily because the forward voltage increases with temperature, ensuring an even distribution of current among all components. They can withstand simultaneous application of high current and high voltage without undergoing destructive failure due to second breakdown. However, at high breakdown voltages (>~200V) the on-state voltage drop of the power MOSFET becomes higher than that of a similar size bipolar device with similar voltage rating, making it more attractive to use the bipolar power transistor at the expense of worse high-frequency performance.</div><div><br />
</div><div>Breakdown voltage (BVDSS) is the drain-to-source voltage at which a current of 250µA starts to flow between source and drain while the gate and the source are shorted together. With no bias on the gate, the drain voltage is entirely supported by the reverse-biased body-drain p-n junction. Breakdown voltage is primarily determined by the resistivity of the epitaxial layer.</div><div><br />
</div><div>All applications of power MOSFET switches require some guardbanding when specifying BVDSS rating. It is important to remember that there is a price to be paid for this in the form of either higher RDS(on) or larger die. There may be applications where a reduction of conservative guardbanding on BVDSS can be justified by an improved RDS(on) specification or lower cost without jeopardizing performance or reliability.</div><div><br />
</div><div>Bipolar transistors have ratings for maximum current under continuous and pulsed conditions. Exceeding these ratings usually result in device failure. Current ratings on MOSFET transistors have a different meaning because they behave as a resistor when they turn on. This means that the maximum voltage drop or heat generated determines the maximum current. Turning the current on and off at high speeds reduces the average power or heat generated, thereby increasing the maximum allowable current.</div><div><br />
</div><div><br />
</div><div><div class="MsoNormal" style="line-height: 150%; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto;"><span lang="EN-US" style="font-family: Sylfaen, serif; font-size: 12pt; line-height: 150%;">Freddy Vallenilla EES</span></div></div></span>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-37107505702072381912010-07-23T20:33:00.002-04:302010-07-25T10:25:14.642-04:30Power MOSFET<div><span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Power MOSFETs are well known for superior switching speed, and they require very little gate drive power because of the insulated gate. In these respects, power MOSFETs approach the characteristics of an "ideal switch". The main drawback is on-resistance R<sub>DS(on)</sub> and its strong positive temperature coefficient. This application note explains these and other main features of high voltage N-channel power MOSFETs, and provides useful information for device selection and application. Microsemi's Advanced Power Technology MOSFET datasheet information is also explained.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>Power MOSFET structure</b> </span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Figure 1 shows a cross section of an APT N-channel power MOSFET structure. (Only N-channel MOSFETs are discussed here.) A positive voltage applied from the source to gate terminals causes electrons to be drawn toward the gate terminal in the body region. If the gate-source voltage is at or above what is called the threshold voltage, enough electrons accumulate under the gate to cause an inversion n-type layer; forming a conductive channel across the body region (the MOSFET is enhanced). Electrons can flow in either direction through the channel. Positive (or forward) drain current flows into the drain as electrons move from the source toward the drain. Forward drain current is blocked once the channel is turned off, and drain-source voltage is supported by the reverse biased body-drain p-n junction. In N-channel MOSFETs, only electrons flow during forward conduction — there are no minority carriers. Switching speed is only limited by the rate that charge is supplied to or removed from capacitances in the MOSFET. Therefore switching can be very fast, resulting in low switching losses. This is what makes power MOSFETs so efficient at high switching frequency.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="center" class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><img alt="N-Channel MOSFET" src="http://i.cmpnet.com/powermanagementdesignline/2006/12/Microsemi_PowerMOSFETP1_Fig1.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></span> </span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">On Resistance R<sub>DS(on)</sub></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">The main components of on-resistance R<sub>DS(on)</sub> include the channel, JFET (accumulation layer), drift region, and parasitics (metallization, bond wires, and package). At voltage ratings above about 150V, drift region resistance dominates R<sub>DS(on)</sub>.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="center" class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"> </span><img alt="RDS-ON versus Current" src="http://i.cmpnet.com/powermanagementdesignline/2006/12/Microsemi_PowerMOSFETP1_Fig2.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div align="center" class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Figure 2 R<sub>DS(on)</sub> vs. Current</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">The effect of current on R<sub>DS(on)</sub> is relatively weak in high voltage MOSFETs . Looking at Figure 2, doubling the current results in only about a 6% increase in R</span><sub><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">RDS(on)</span></sub><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><img alt="RDS-ON versus Temperature" src="http://i.cmpnet.com/powermanagementdesignline/2006/12/Microsemi_PowerMOSFETP1_Fig3.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Figure 3 R<sub>DS(on)</sub> vs. Temperature</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Temperature on the other hand has a strong effect on R</span><sub><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">RDS(on)</span></sub><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">. As seen in Figure 3, on resistance approximately doubles from 25°C to 125°C. The temperature coefficient of R<sub>DS(on)</sub> is the slope of the curve in Figure 3 and is always positive because of majority-only carriers. The strong positive R<sub>DS(on)</sub> temperature coefficient compounds the I<sup>2</sup>R conduction loss as temperature increases.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">The positive R<sub>DS(on)</sub> temperature coefficient is a nice feature when paralleling power MOSFETs because it ensures thermal stability. It does not however ensure even current sharing. This is a common misconception. What really makes MOSFETs so easy to parallel is their relatively narrow part-to-part parameter distribution, particularly R</span><sub><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">RDS(on)</span></sub><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">, combined with the security from current hogging provided by the positive R<sub>DS(on)</sub> temperature coefficient.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">For any given die size, R<sub>DS(on)</sub> also increases with increasing voltage rating V<sub>(BR)DSS</sub>, as shown Figure 4.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><img alt="RDS-ON versus Voltage" src="http://i.cmpnet.com/powermanagementdesignline/2006/12/Microsemi_PowerMOSFETP1_Fig4.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Figure 4 Normalized R<sub>DS(on)</sub> vs. V<sub>(BR)DSS</sub></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">A curve fit of rated R<sub>DS(on)</sub> versus V<sub>(BR)DSS</sub> for Power MOS V and Power MOS 7 MOSFETs reveals that R</span><sub><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">RDS(on)</span></sub><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"> increases as the square of V<sub>(BR)DSS</sub>. This nonlinear relationship between R</span><sub><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">DS(on)</span></sub><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"> and V<sub>(BR)DSS</sub> is a compelling reason to research ways to reduce the conduction loss of power transistors.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>JFET </b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Within the structure of a MOSFET, you can imagine an integral JFET shown in Figure 1. This JFET has a significant influence on R<sub>DS(on)</sub> and is part of the normal operation of the MOSFET.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>Intrinsic body diode</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">The body-drain p-n junction forms an intrinsic diode called the body diode (see Figure 1). Reverse drain current cannot be blocked because the body is shorted to the source, providing a high current path through the body diode. Enhancing the device reduces conduction loss when reverse drain current flows because electrons flow through the channel in addition to electrons and minority carriers flowing through the body diode.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">The intrinsic body diode is convenient in circuits that require a path for reverse drain current (often called freewheeling current), such as bridge circuits. For these circuits, FREDFETs are offered with improved reverse recovery characteristics. FREDFET is simply a trade name Advanced Power Technology uses to distinguish a MOSFET that has additional processing steps to speed up the reverse recovery of the intrinsic body diode. There is no separate diode in a FREDFET; it is the MOSFET intrinsic body diode. Either electron irradiation (which is usually used) or platinum doping is used for minority carrier lifetime control in the body diode, greatly reducing the reverse recovery charge and time.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">A side effect of FREDFET processing is higher leakage current, particularly at high temperature. However, considering that MOSFETs have low leakage current to begin with, the added leakage current of a FREDFET is normally of no concern below 150°C junction temperature. Depending on the irradiation dose, a FREDFET may have a higher R<sub>DS(on)</sub> rating than a corresponding MOSFET. The body diode forward voltage is also slightly higher for a FREDFET. Gate charge and switching speed are identical between MOSFETs and FREDFETs. From here on, the term MOSFET will be used for both MOSFETs and FREDFETs unless specifically stated otherwise.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">The reverse recovery performance of a MOSFET or even of a FREDFET is "crummy" compared to a discrete fast recovery diode. In a hard switched application operating at 125°C, the turn-on loss in the switch due to the reverse recovery current of the body diode is about five times higher than if a discrete fast recovery diode is used. There are two reasons for this:</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">1.-The area of the body diode is the same as the area of the MOSFET or FREDFET, whereas the area of a discrete diode for the same function can be much smaller and hence have much lower recovery charge.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">2.- The body diode of a MOSFET or even a FREDFET is not optimized for reverse recovery like a discrete diode is.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Like any conventional silicon diode, body diode reverse recovery charge and time depend on temperature, di/dt, and current. The forward voltage of the body diode, V<sub>SD</sub>, decreases with temperature by about 2.5 mV/°C.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>Parasitic bipolar transistor</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">The layered MOSFET structure also forms a parasitic NPN bipolar junction transistor (BJT), and turning it on is definitely not part of normal operation. If the BJT were to turn on and saturate, it would result in a condition called latchup, where the MOSFET cannot be turned off except by externally interrupting the drain current. High power dissipation during latchup can destroy the device.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">The base of the parasitic BJT is shorted to the source to prevent latchup and because breakdown voltage would be greatly reduced (for the same </span><sub><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">RDS(on)</span></sub><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">) if the base were allowed to float. It is theoretically possible for extremely high dv/dt during turn-off to cause latchup. For modern, conventional power MOSFETs however, it is very difficult to build a circuit capable of achieving such high dv/dt.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">There is a risk of turning on the parasitic BJT if the body diode conducts and then commutates off with excessively high dv/dt. High commutation dv/dt causes high current density of minority carriers (positive carriers, or holes) in the body region, which can build up enough voltage across the body resistance to turn on the parasitic BJT. This is the reason for the peak commutating (body diode recovery) dv/dt limit in the datasheet. Peak commutating dv/dt is higher for a FREDFET compared to a MOSFET because of reduced minority carrier lifetime.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>Switching speed</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Switching speed and loss are practically unaffected by temperature because the capacitances are unaffected by temperature. Reverse recovery current in a diode however increases with temperature, so temperature effects of an external diode (be it a discrete diode or a MOSFET or FREDFET body diode) in the power circuit affect turn-on switching loss.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>Threshold voltage</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">The threshold voltage, denoted as V<sub>GS(th)</sub>, is really a turn-off specification. It tells how many milliamps of drain current will flow at the threshold voltage, so the device is basically off but on the verge of turning on. The threshold voltage has a negative temperature coefficient, meaning the threshold voltage decreases with increasing temperature. This temperature coefficient affects turn-on and turn-off delay times and hence the dead-time requirement in a bridge circuit.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><img alt="Transfer Characteristics" src="http://i.cmpnet.com/powermanagementdesignline/2006/12/Microsemi_PowerMOSFETP1_Fig5.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Figure 5 Transfer Characteristic Example</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Transfer characteristic</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Figure 5 shows the transfer characteristic for an APT50M75B2LL MOSFET. The transfer characteristic depends on both temperature and drain current. In Figure 5, below 100 Amps the gate-source voltage has a negative temperature coefficient (less gate-source voltage at higher temperature for a given drain current). Above 100 Amps, the temperature coefficient is positive. The gate-source voltage temperature coefficient and the drain current at which it crosses over from negative to positive are important for linear mode operation.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>Breakdown voltage</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Breakdown voltage has a positive temperature coefficient, as will be discussed in the Walkthrough section.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>Short circuit capability</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Short circuit withstand capability is not typically listed in the datasheet. This is simply because conventional power MOSFETs are unmatched for short circuit withstand capability compared to IGBTs or other devices with higher current density. It goes without saying that MOSFETs and FREDFETs are short circuit capable.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>Maximum Ratings</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b><br />
</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>V</b><sub><b>DSS</b></sub><b> — Drain-source voltage</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">This is a rating of the maximum drain-source voltage without causing avalanche breakdown, with the gate shorted to the source and the device at 25°C. Depending on temperature, the avalanche breakdown voltage could actually be less than the VDSS rating. See the description of V<sub>(BR)DSS</sub> in Static Electrical Characteristics.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>V</b><sub><b>GS</b></sub><b> — Gate-source voltage</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">VGS is a rating of the maximum voltage between the gate and source terminals. The purpose of this rating is to prevent damage of the gate oxide. The actual gate oxide withstand voltage is typically much higher than this but varies due to manufacturing processes, so staying within this rating ensures application reliability.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>I</b><sub><b>D</b></sub><b> — Continuous drain current</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">I<sub>D</sub> is a rating of the maximum continuous DC current with the die at its maximum rated junction temperature TJ(max) and the case at 25°C and sometimes also at a higher temperature. It is based on the junction-to-case thermal resistance rating R</span><span style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">θ</span><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">JC and the case temperature TC as follows:</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><img alt="Equation 1" src="http://i.cmpnet.com/powermanagementdesignline/2006/12/Microsemi_PowerMOSFETP1_Eq1.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></span>Eq 1</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">This equation simply says that the maximum heat that can be dissipated, </span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"> </span><img alt="Equation 1a" src="http://i.cmpnet.com/powermanagementdesignline/2006/12/Microsemi_PowerMOSFETP1_Eq1a.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">equals the maximum allowable heat generated by conduction loss, I<sup>2</sup><sub>D</sub> X R<sub>DS(on)@TJ(max)</sub>, where R<sub>DS(on)@TJ (max) </sub>is the ON-resistance at the maximum junction temperature.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Solving for I<sub>D</sub></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><sub><br />
</sub></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><img alt="Equation 2" src="http://i.cmpnet.com/powermanagementdesignline/2006/12/Microsemi_PowerMOSFETP1_Eq2.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></span>Eq 2</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Note that there are no switching losses involved in I<sub>D</sub>, and holding the case at 25°C is seldom feasible in practice. Because of this, actual switched current is typically less than half of the I<sub>D</sub> @ T<sub>C</sub> = 25°C rating in a hard switched application; one fourth to one third is common.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>Graph of I</b><sub><b>D</b></sub><b> versus T</b><sub><b>C</b></sub></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">This graph is simply the solution to (2) over a range of case temperatures. Switching losses are not included. Figure 6 shows an example. Note that in some cases, the package leads limit the continuous current (switched current can be higher): 100 Amps for TO-247 and TO-264 packages, 75 Amps for TO-220 package, and 220 Amps for the SOT-227 package.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><img alt="Drain versus Case Temperature" height="180" src="http://i.cmpnet.com/powermanagementdesignline/2006/12/Microsemi_PowerMOSFETP1_Fig6.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Figure 6 Maximum drain current vs. case temperature</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>I</b><sub><b>DM</b></sub><b> — Pulsed drain current</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">This rating indicates how much pulsed current the device can handle, which is significantly higher than the rated continuous DC current. The purposes of the IDM rating are:</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">To keep the MOSFET operating in the Ohmic region of its output characteristic. See Figure 7. There is a maximum drain current for a corresponding gate-source voltage that a MOSFET will conduct. If the operating point at a given gate-source voltage goes above the Ohmic region "knee" in Figure 7, any further increase in drain current results in a significant rise in drain-source voltage (linear mode operation) and a consequent rise in conduction loss. If power dissipation is too high for too long the device may fail. The IDM rating is set below the "knee" for typical gate drive voltages.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">A current density limit to prevent die heating that otherwise could result in a burnout site.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">To avoid problems with excessive current through the bond wires in case the bond wires are the "weak link" instead of the die.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><img alt="MOSFET Output Characteristics" height="179" src="http://i.cmpnet.com/powermanagementdesignline/2006/12/Microsemi_PowerMOSFETP1_Fig7.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Figure 7 MOSFET Output Characteristic</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>P</b><sub><b>D</b></sub><b> — Total power dissipation</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">This is a rating of the maximum power that the device can dissipate and is based on the maximum junction temperature and the thermal resistance RqJC at a case temperature of 25°C.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><img alt="Equation 3" src="http://i.cmpnet.com/powermanagementdesignline/2006/12/Microsemi_PowerMOSFETP1_Eq3.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></span>Eq 3</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">The linear derating factor is simply the inverse of R</span><sub><span style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">θ</span></sub><sub><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">JC</span></sub><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>T</b><sub><b>J</b></sub><b>, T</b><sub><b>STG </b></sub><b>— Operating and storage junction temperature range</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">This is the range of permissible storage and operating junction temperatures. The limits of this range are set to ensure a minimum acceptable device service life. Operating well within the limits of this range can significantly enhance the service life.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>E</b><sub><b>AS</b></sub><b> — Single pulse avalanche energy</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">If a voltage overshoot (typically due to leakage and stray inductances) does not exceed the breakdown voltage, then the device will not avalanche and hence does not need to dissipate avalanche energy. Avalanche energy rated devices offer a safety net for over-voltage transients, depending on the amount of energy dissipated in avalanche mode.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">All devices that are avalanche energy rated have an EAS rating. Avalanche energy rated is synonymous with unclamped inductive switching (UIS) rated. EAS indicates how much reverse avalanche energy the device can safely absorb.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">Conditions for a test circuit are stated in a footnote, and the EAS rating is equal to </span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><img alt="EAS Equation" src="http://i.cmpnet.com/powermanagementdesignline/2006/12/Microsemi_PowerMOSFETP1_EqEAS.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" /></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">where L is the value of an inductor carrying a peak current iD, which is suddenly diverted into the drain of the device under test. It is the inductor voltage exceeding the breakdown voltage of the MOSFET that causes the avalanche condition. An avalanche condition allows the inductor current to flow through the MOSFET, even though the MOSFET is in the off state. Energy stored in the inductor is analogous to energy stored in leakage and/or stray inductances and is dissipated in the MOSFET.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">When MOSFETs are paralleled, it is highly unlikely that they have exactly the same breakdown voltage. Typically, one device will avalanche first and subsequently take all the avalanche current (energy).</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>E</b><sub><b>AR</b></sub><b> — Repetitive avalanche energylanche energy</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">A repetitive avalanche rating has become "industry standard" but is meaningless without information about the frequency, other losses, and the amount of cooling. Heat dissipation (cooling) often limits the repetitive avalanche energy. It is also difficult to predict how much energy is in an avalanche event. What the EAR rating really says is that the device can withstand repetitive avalanche without any frequency limitation, provided the device is not overheated, which is true of any avalanche capable device. During design qualification, it is good practice to measure the device or heat sink temperature during operation to see that the MOSFET does not overheat, especially if avalanching is possible.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><b>I</b><sub><b>AR</b></sub><b> — Avalanche current</b></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">For some devices, the propensity for current crowding in the die during avalanche mandates a limit in avalanche current IAR. Thus avalanche current is the "fine print" of avalanche energy specifications; it reveals the true capability of a device.</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><br />
</span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span lang="EN-US" style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"></span></div><div class="MsoNormal"><span lang="EN-US" style="font-family: 'Times New Roman', serif; font-size: 12pt; line-height: 115%;">Freddy Vallenilla. EES</span></div></span></div>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-52750305265710150162010-07-23T18:52:00.001-04:302010-07-25T10:24:49.245-04:30Semiconductor manufacturing techniques<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><br />
</div><div>The manufacture of only silicon based semiconductors is described in this section; most semiconductors are silicon. Silicon is particularly suitable for integrated circuits because it readily forms an oxide coating, useful in patterning integrated components like transistors.</div><div><br />
</div><div>Silicon is the second most common element in the Earth's crust in the form of silicon dioxide, SiO2, otherwise known as silica sand. Silicon is freed from silicon dioxide by reduction with carbon in an electric arc furnace</div><div><br />
</div><div style="text-align: center;"><span class="Apple-style-span" style="font-family: Arial, sans-serif; font-size: 12px; line-height: 13px;">SiO<sub>2</sub> + C = CO<sub>2</sub>+ Si</span></div><div style="text-align: center;"><span class="Apple-style-span" style="font-family: Arial, sans-serif; font-size: 12px; line-height: 13px;"><br />
</span></div><div class="MsoNormal" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-family: 'Times New Roman', serif;"></span></div><div>Such metalurgical grade silicon is suitable for use in silicon steel transformer laminations, but not nearly pure enough for semiconductor applications. Conversion to the chloride SiCl4 (or SiHCl3) allows purification by fractional distillation. Reduction by ultrapure zinc or magnesium yields sponge silicon, requiring further purification. Or, thermal decomposition on a hot polycrystalline silicon rod heater by hydrogen yields ultra pure silicon.</div><div><br />
</div><div style="text-align: center;"><span class="Apple-style-span" style="font-family: Arial, sans-serif; font-size: 12px;">Si + 3HCl = SiHCl</span><span class="Apple-style-span" style="font-family: Arial, sans-serif; font-size: 12px;"><sub>3</sub></span><span class="Apple-style-span" style="font-family: Arial, sans-serif; font-size: 12px;"> + H</span><span class="Apple-style-span" style="font-family: Arial, sans-serif; font-size: 12px;"><sub>2</sub></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span style="color: black; font-family: Arial, sans-serif; font-size: 9pt;">SiHCl<sub>3</sub> + H<sub>2</sub> = Si + 3HCl<sub>2</sub></span></div><div class="MsoNormal" style="line-height: normal; margin-bottom: 0.0001pt; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span style="color: black; font-family: Arial, sans-serif; font-size: 9pt;"><sub><br />
</sub></span></div><div>The polycrystalline silicon is melted in a fused silica crucible heated by an induction heated graphite suceptor. The graphite heater may alternately be directly driven by a low voltage at high current. In the Czochralski process, the silicon melt is solidified on to a pencil sized monocrystal silicon rod of the desired crystal lattice orientation. (Figure below) The rod is rotated and pulled upward at a rate to encourage the diameter to expand to several inches. Once this diameter is attained, the boule is automatically pulled at a rate to maintain a constant diameter to a length of a few feet. Dopants may be added to the crucible melt to create, for example, a P-type semiconductor. The growing apparatus is enclosed within an inert atmosphere.</div><div><br />
</div><div style="text-align: center;"> <img height="131" src="http://sub.allaboutcircuits.com/images/03425.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div>Czochralski monocrystalline silicon growth.</div><div><br />
</div><div>The finished boule is ground to a precise final diameter, and the ends trimmed. The boule is sliced into wafers by an inside diameter diamond saw. The wafers are ground flat and polished. The wafers could have an N-type epitaxial layer grown atop the wafer by thermal deposition for higher quality. Wafers at this stage of manufacture are delivered by the silicon wafer manufacturer to the semiconductor manufacturer.</div><div><br />
</div><div style="text-align: center;"><img height="140" src="http://sub.allaboutcircuits.com/images/03426.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /> </div><div><br />
</div><div>Silicon boule is diamond sawed into wafers.</div><div><br />
</div><div>The processing of semiconductors involves photo lithography, a process for making metal lithographic printing plates by acid etching. The electronics based version of this is the processing of copper printed circuit boards. This is reviewed in Figure below as an easy introduction to the photo lithography involved in semiconductor processing.</div><div><br />
</div><div style="text-align: center;"> <img height="85" src="http://sub.allaboutcircuits.com/images/03429.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div>Processing of copper printed circuit boards is similar to the photo lithographic steps of semiconductor processing.</div><div><br />
</div><div>We start with a copper foil laminated to an epoxy fiberglass board in Figure above (a). We also need positive artwork with black lines corresponding to the copper wiring lines and pads that are to remain on the finished board. Positive artwork is required because positive acting resist is used. Though, negative resist is available for both circuit boards and semiconductor processing. At (b) the liquid positive photo resist is applied to the copper face of the printed circuit board (PCB). It is allowed to dry and may be baked in an oven. The artwork may be a plastic film positive reproduction of the original artwork scaled to the required size. The artwork is placed in contact with the circuit board under a glass plate at (c). The board is exposed to ultraviolet light (d) to form a latent image of softened photo resist. The artwork is removed (e) and the softened resist washed away by an alkaline solution (f). The rinsed and dried (baked) circuit board has a hardened resist image atop the copper lines and pads that are to remain after etching. The board is immersed in the etchant (g) to remove copper not protected by hardened resist. The etched board is rinsed and the resist removed by a solvent.</div><div><br />
</div><div>The major difference in the patterning of semiconductors is that a silicon dioxide layer atop the wafer takes the place of the resist during the high temperature processing steps. Though, the resist is required in low temperature wet processing to pattern the silicon dioxide.</div><div><br />
</div><div>An N-type doped silicon wafer in Figure below (a) is the starting material in the manufacture of semiconductor junctions. A silicon dioxide layer (b) is grown atop the wafer in the presence of oxygen or water vapor at high temperature (over 1000o C in a diffusion furnace. A pool of resist is applied to the center of the cooled wafer, then spun in a vacuum chuck to evenly distribute the resist. The baked on resist (c) has a chrome on glass mask applied to the wafer at (d). This mask contains a pattern of windows which is exposed to ultraviolet light (e).</div><div><br />
</div><div style="text-align: center;"> <img height="116" src="http://sub.allaboutcircuits.com/images/03427.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div>Manufacture of a silicon diode junction.</div><div><br />
</div><div>After the mask is removed in Figure above (f), the positive resist can be developed (g) in an alkaline solution, opening windows in the UV softened resist. The purpose of the resist is to protect the silicon dioxide from the hydrofluoric acid etch (h), leaving only open windows corresponding to the mask openings. The remaining resist (i) is stripped from the wafer before returning to the diffusion furnace. The wafer is exposed to a gaseous P-type dopant at high temperature in a diffusion furnace (j). The dopant only diffuses into the silicon through the openings in the silicon dioxide layer. Each P-diffusion through an opening produces a PN junction. If diodes were the desired product, the wafer would be diamond scribed and broken into individual diode chips. However, the whole wafer may be processed further into bipolar junction transistors.</div><div><br />
</div><div>To convert the diodes into transistors, a small N-type diffusion in the middle of the existing P-region is required. Repeating the previous steps with a mask having smaller openings accomplishes this. Though not shown in Figure above (j), an oxide layer was probably formed in that step during the P-diffusion. The oxide layer over the P-diffusion is shown in Figure below (k). Positive photo resist is applied and dried (l). The chrome on glass emitter mask is applied (m), and UV exposed (n). The mask is removed (o). The UV softened resist in the emitter opening is removed with an alkaline solution (p). The exposed silicon dioxide is etched away with hydrofluoric acid (HF) at (q)</div><div><br />
</div><div style="text-align: center;"> <img height="121" src="http://sub.allaboutcircuits.com/images/03428.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div>Manufacture of a bipolar junction transistor, continuation of Manufacture of a silicon diode junction.</div><div><br />
</div><div>After the unexposed resist is stripped from the wafer (r), it is placed in a diffusion furnace (Figure above (s) for high temperature processing. An N-type gaseous dopant, such phosphorus oxychloride (POCl) diffuses through the small emitter window in the oxide (s). This creates NPN layers corresponding to the emitter, base, and collector of a BJT. It is important that the N-type emitter not be driven all the way through the P-type base, shorting the emitter and collector. The base region between the emitter and collector also needs to be thin so that the transistor has a useful β. Otherwise, a thick base region could form a pair of diodes rather than a transistor. At (t) metalization is shown making contact with the transistor regions. This requires a repeat of the previous steps (not shown here) with a mask for contact openings through the oxide. Another repeat with another mask defines the metalization pattern atop the oxide and contacting the transistor regions through the openings.</div><div><br />
</div><div>The metalization could connect numerous transistors and other components into an integrated circuit. Though, only one transistor is shown. The finished wafer is diamond scribed and broken into individual dies for packaging. Fine gauge aluminum wire bonds the metalized contacts on the die to a lead frame, which brings the contacts out of the final package.</div><div><br />
</div><div><br />
</div><div><div class="MsoNormal" style="line-height: normal;"><span lang="EN-US" style="font-family: 'Times New Roman', serif; font-size: 12pt;">Freddy Vallenilla Roa. EES</span></div></div></span>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-62198854324823332922010-07-23T18:37:00.002-04:302010-07-25T10:24:25.707-04:30Junction field-effect transistors<div><br />
</div><span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div>The field effect transistor was proposed by Julius Lilienfeld in US patents in 1926 and 1933 (1,900,018). Moreover, Shockley, Brattain, and Bardeen were investigating the field effect transistor in 1947. Though, the extreme difficulties sidetracked them into inventing the bipolar transistor instead. Shockley's field effect transistor theory was published in 1952. However, the materials processing technology was not mature enough until 1960 when John Atalla produced a working device.</div><div><br />
</div><div>A field effect transistor (FET) is a unipolar device, conducting a current using only one kind of charge carrier. If based on an N-type slab of semiconductor, the carriers are electrons. Conversely, a P-type based device uses only holes.</div><div><br />
</div><div>At the circuit level, field effect transistor operation is simple. A voltage applied to the gate, input element, controls the resistance of the channel, the unipolar region between the gate regions. (Figure below) In an N-channel device, this is a lightly doped N-type slab of silicon with terminals at the ends. The source and drain terminals are analogous to the emitter and collector, respectively, of a BJT. In an N-channel device, a heavy P-type region on both sides of the center of the slab serves as a control electrode, the gate. The gate is analogous to the base of a BJT.</div><div><br />
</div><div>"Cleanliness is next to godliness" applies to the manufacture of field effect transistors. Though it is possible to make bipolar transistors outside of a clean room, it is a necessity for field effect transistors. Even in such an environment, manufacture is tricky because of contamination control issues. The unipolar field effect transistor is conceptually simple, but difficult to manufacture. Most transistors today are a metal oxide semiconductor variety (later section) of the field effect transistor contained within integrated circuits. However, discrete JFET devices are available.</div><div><br />
</div><div style="text-align: center;"> <img height="140" src="http://sub.allaboutcircuits.com/images/03415.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div>Junction field effect transistor cross-section.</div><div><br />
</div><div>A properly biased N-channel junction field effect transistor (JFET) is shown in Figure above. The gate constitutes a diode junction to the source to drain semiconductor slab. The gate is reverse biased. If a voltage (or an ohmmeter) were applied between the source and drain, the N-type bar would conduct in either direction because of the doping. Neither gate nor gate bias is required for conduction. If a gate junction is formed as shown, conduction can be controlled by the degree of reverse bias.</div><div><br />
</div><div>Figure below(a) shows the depletion region at the gate junction. This is due to diffusion of holes from the P-type gate region into the N-type channel, giving the charge separation about the junction, with a non-conductive depletion region at the junction. The depletion region extends more deeply into the channel side due to the heavy gate doping and light channel doping.</div><div><br />
</div><div style="text-align: center;"><img height="84" src="http://sub.allaboutcircuits.com/images/03416.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /> </div><div><br />
</div><div>N-channel JFET: (a) Depletion at gate diode. (b) Reverse biased gate diode increases depletion region. (c) Increasing reverse bias enlarges depletion region. (d) Increasing reverse bias pinches-off the S-D channel.</div><div><br />
</div><div>The thickness of the depletion region can be increased Figure above(b) by applying moderate reverse bias. This increases the resistance of the source to drain channel by narrowing the channel. Increasing the reverse bias at (c) increases the depletion region, decreases the channel width, and increases the channel resistance. Increasing the reverse bias VGS at (d) will pinch-off the channel current. The channel resistance will be very high. This VGS at which pinch-off occurs is VP, the pinch-off voltage. It is typically a few volts. In summation, the channel resistance can be controlled by the degree of reverse biasing on the gate.</div><div><br />
</div><div>The source and drain are interchangeable, and the source to drain current may flow in either direction for low level drain battery voltage (< 0.6 V). That is, the drain battery may be replaced by a low voltage AC source. For a high drain power supply voltage, to 10's of volts for small signal devices, the polarity must be as indicated in Figure below(a). This drain power supply, not shown in previous figures, distorts the depletion region, enlarging it on the drain side of the gate. This is a more correct representation for common DC drain supply voltages, from a few to tens of volts. As drain voltage VDS is increased,the gate depletion region expands toward the drain. This increases the length of the narrow channel, increasing its resistance a little. We say "a little" because large resistance changes are due to changing gate bias. Figure below(b) shows the schematic symbol for an N-channel field effect transistor compared to the silicon cross-section at (a). The gate arrow points in the same direction as a junction diode. The "pointing" arrow and "non-pointing" bar correspond to P and N-type semiconductors, respectively.</div><div><br />
</div><div style="text-align: center;"> <img height="55" src="http://sub.allaboutcircuits.com/images/03417.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div>N-channel JFET electron current flow from source to drain in (a) cross-section, (b) schematic symbol.</div><div><br />
</div><div>Figure above shows a large electron current flow from (-) battery terminal, to FET source, out the drain, returning to the (+) battery terminal. This current flow may be controlled by varying the gate voltage. A load in series with the battery sees an amplified version of the changing gate voltage.</div><div><br />
</div><div>P-channel field effect transistors are also available. The channel is made of P-type material. The gate is a heavily dopped N-type region. All the voltage sources are reversed in the P-channel circuit (Figure below) as compared with the more popular N-channel device. Also note, the arrow points out of the gate of the schematic symbol (b) of the P-channel field effect transistor.</div><div><br />
</div><div style="text-align: center;"> <img height="47" src="http://sub.allaboutcircuits.com/images/03418.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div>P-channel JFET: (a) N-type gate, P-type channel, reversed voltage sources compared with N-channel device. (b) Note reversed gate arrow and voltage sources on schematic.</div><div><br />
</div><div>As the positive gate bias voltage is increased, the resistance of the P-channel increases, decreasing the current flow in the drain circuit.</div><div><br />
</div><div>Discrete devices are manufactured with the cross-section shown in Figure below. The cross-section, oriented so that it corresponds to the schematic symbol, is upside down with respect to a semiconductor wafer. That is, the gate connections are on the top of the wafer. The gate is heavily doped, P+, to diffuse holes well into the channel for a large depletion region. The source and drain connections in this N-channel device are heavily doped, N+ to lower connection resistance. However, the channel surrounding the gate is lightly doped to allow holes from the gate to diffuse deeply into the channel. That is the N- region.</div><div><br />
</div><div style="text-align: center;"> <img height="91" src="http://sub.allaboutcircuits.com/images/03303.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div>Junction field effect transistor: (a) Discrete device cross-section, (b) schematic symbol, (c) integrated circuit device cross-section.</div><div><br />
</div><div>All three FET terminals are available on the top of the die for the integrated circuit version so that a metalization layer (not shown) can interconnect multiple components. (Figure above(c) ) Integrated circuit FET's are used in analog circuits for the high gate input resistance.. The N-channel region under the gate must be very thin so that the intrinsic region about the gate can control and pinch-off the channel. Thus, gate regions on both sides of the channel are not necessary.</div><div><br />
</div><div style="text-align: center;"> <img height="112" src="http://sub.allaboutcircuits.com/images/03304.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div>Junction field effect transistor (static induction type): (a) Cross-section, (b) schematic symbol.</div><div><br />
</div><div>The static induction field effect transistor (SIT) is a short channel device with a buried gate. (Figure above) It is a power device, as opposed to a small signal device. The low gate resistance and low gate to source capacitance make for a fast switching device. The SIT is capable of hundreds of amps and thousands of volts. And, is said to be capable of an incredible frequency of 10 gHz.</div><div><br />
</div><div style="text-align: center;"> <img height="46" src="http://sub.allaboutcircuits.com/images/03451.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></div><div><br />
</div><div>Metal semiconductor field effect transistor (MESFET): (a) schematic symbol, (b) cross-section.</div><div><br />
</div><div>The Metal semiconductor field effect transistor (MESFET) is similar to a JFET except the gate is a schottky diode instead of a junction diode. A schottky diode is a metal rectifying contact to a semiconductor compared with a more common ohmic contact. In Figure above the the source and drain are heavily doped (N+). The channel is lightly doped (N-). MESFET's are higher speed than JFET's. The MESET is a depletion mode device, normally on, like a JFET. They are used as microwave power amplifiers to 30 gHz. MESFET's can be fabricated from silicon, gallium arsenide, indium phosphide, silicon carbide, and the diamond allotrope of carbon.</div><div><br />
</div><div><br />
</div></span><br />
<div><br />
</div><div><span lang="EN-US" style="font-family: 'Times New Roman', serif; font-size: 12pt; line-height: 115%;">Freddy Vallenilla Roa. EES</span></div>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-10784346709105265542010-07-21T22:12:00.002-04:302010-07-25T10:24:07.632-04:30The MOSFET<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span><br />
<span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><h2 style="font-size: 12pt; font-weight: bold; text-align: left; text-decoration: underline;"><span class="Apple-style-span" style="color: black; font-family: georgia, serif;"><br />
</span></h2><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">As well as the Junction Field Effect Transistor, there is another type of Field Effect Transistor available whose </span></span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Gate</span></span></span><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> input is electrically insulated from the main current carrying channel and is therefore called an </span></span><strong><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Insulated Gate Field Effect Transistor</span></span></strong><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">. The most common type of insulated gate FET or IGFET as it is sometimes called, is the </span></span><b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Metal Oxide Semiconductor Field Effect Transistor</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> or </span></span><strong><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">MOSFET</span></span></strong><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> for short.</span></span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The </span></span><strong><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">MOSFET</span></span></strong><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> type of field effect transistor has a "Metal Oxide" </span></span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span></span><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> (usually silicon dioxide commonly known as glass), which is electrically insulated from the main semiconductor N-channel or P-channel. This isolation of the controlling </span></span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span></span><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> makes the input resistance of the </span></span><strong><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">MOSFET</span></span></strong><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> extremely high in the Mega-ohms region and almost infinite. As the </span></span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span></span><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> terminal is isolated from the main current carrying channel ""NO current flows into the gate"" and like the JFET, the </span></span><strong><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">MOSFET</span></span></strong><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> also acts like a voltage controlled resistor. Also like the JFET, this very high input resistance can easily accumulate large static charges resulting in the </span></span><strong><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">MOSFET</span></span></strong><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> becoming easily damaged unless carefully handled or protected.</span></span></div><h3 style="font-size: 10pt; text-align: left; text-decoration: underline;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Basic MOSFET Structure and Symbol</span></span></h3><div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span></div><div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span></div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="font-size: 9pt; text-align: left; width: 510px;"><tbody>
<tr><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
<img alt="Metal Oxide Semiconductor FET" border="0" height="296" src="http://www.electronics-tutorials.ws/transistor/tran20.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="504" /></span></td> </tr>
</tbody></table></span><span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span></span></div><div><span style="font-size: 12px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span></div><div><span style="font-size: 12px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span><br />
<span style="font-size: 12px;"><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">We also saw previously that the </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> of a JFET must be biased in such a way as to forward-bias the PN junction but in a MOSFET device no such limitations applies so it is possible to bias the </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> in either polarity. This makes MOSFET's specially valuable as electronic switches or to make logic gates because with no bias they are normally non-conducting and the high </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> resistance means that very little control current is needed. Both the P-channel and the N-channel MOSFET is available in two basic forms, the</span><strong><span class="Apple-style-span" style="font-family: georgia, serif;">Enhancement</span></strong><span class="Apple-style-span" style="font-family: georgia, serif;"> type and the </span><strong><span class="Apple-style-span" style="font-family: georgia, serif;">Depletion</span></strong><span class="Apple-style-span" style="font-family: georgia, serif;"> type.</span></div><h2 style="font-size: 12pt; font-weight: normal; text-align: left; text-decoration: underline;"><span class="Apple-style-span" style="font-family: georgia, serif;">Depletion-mode MOSFET</span></h2><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The </span><strong><span class="Apple-style-span" style="font-family: georgia, serif;">Depletion-mode MOSFET</span></strong><span class="Apple-style-span" style="font-family: georgia, serif;">, which is less common than the enhancement types is normally switched "ON" without a </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> bias voltage but requires a </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> to </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">source</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> voltage (</span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">V</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">gs</span></sub></span><span class="Apple-style-span" style="font-family: georgia, serif;">) to switch the device "OFF". Similar to the JFET types. For N-channel MOSFET's a "Positive" gate voltage widens the channel, increasing the flow of the </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">drain</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> current and decreasing the </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">drain</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> current as the </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> voltage goes more negative. The opposite is also true for the P-channel types. The depletion mode MOSFET is equivalent to a "Normally Closed" switch.</span></div><h3 style="font-size: 10pt; text-align: left; text-decoration: underline;"><span class="Apple-style-span" style="font-family: georgia, serif;">Depletion-mode N-Channel MOSFET and circuit Symbols</span></h3><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="font-size: 9pt; text-align: left; width: 400px;"><tbody>
<tr align="center"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img alt="Characteristics Curves for Depletion mode MOSFET" border="0" height="294" src="http://www.electronics-tutorials.ws/transistor/tran36.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="359" /></span></td> </tr>
<tr align="center"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
<img alt="Circuit Symbols for Depletion mode MOSFET" border="0" height="203" src="http://www.electronics-tutorials.ws/transistor/tran35.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="376" /></span></td> </tr>
</tbody></table><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Depletion-mode MOSFET's are constructed similar to their JFET transistor counterparts where the </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">drain-source</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> channel is inherently conductive with electrons and holes already present within the N-type or P-type channel. This doping of the channel produces a conducting path of low resistance between the </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">drain</span></span><span class="Apple-style-span" style="font-family: georgia, serif;">and </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">source</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> with zero </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> bias.</span></div><h2 style="font-size: 12pt; font-weight: normal; text-align: left; text-decoration: underline;"><span class="Apple-style-span" style="font-family: georgia, serif;">Enhancement-mode MOSFET</span></h2><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The more common </span><strong><span class="Apple-style-span" style="font-family: georgia, serif;">Enhancement-mode MOSFET</span></strong><span class="Apple-style-span" style="font-family: georgia, serif;"> is the reverse of the depletion-mode type. Here the conducting channel is lightly doped or even undoped making it non-conductive. This results in the device being normally "OFF" when the </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> bias voltage is equal to zero.</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">drain</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> current will only flow when a </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> voltage (</span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">V</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">gs</span></sub></span><span class="Apple-style-span" style="font-family: georgia, serif;">) is applied to the </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> terminal. This positive voltage creates an electrical field within the channel attracting electrons towards the oxide layer and thereby reducing the overall resistance of the channel allowing current to flow. Increasing this positive </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> voltage will cause an increase in the </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">drain</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> current, </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">I</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">d</span></sub></span><span class="Apple-style-span" style="font-family: georgia, serif;"> through the channel. Then, the Enhancement-mode device is equivalent to a "Normally Open" switch.</span></div><h3 style="font-size: 10pt; text-align: left; text-decoration: underline;"><span class="Apple-style-span" style="font-family: georgia, serif;">Enhancement-mode N-Channel MOSFET and circuit Symbols</span></h3><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="font-size: 9pt; text-align: left; width: 400px;"><tbody>
<tr align="center"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img alt="Characteristics Curves for Enhancement mode MOSFET" border="0" height="294" src="http://www.electronics-tutorials.ws/transistor/tran37.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="359" /></span></td> </tr>
<tr align="center"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
<img alt="Circuit Symbols for Enhancement mode MOSFET" border="0" height="203" src="http://www.electronics-tutorials.ws/transistor/tran19.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="376" /></span></td> </tr>
</tbody></table><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Enhancement-mode MOSFET's make excellent electronics switches due to their low "ON" resistance and extremely high "OFF" resistance and extremely high </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> resistance. Enhancement-mode MOSFET's are used in integrated circuits to produce CMOS type </span><em><span class="Apple-style-span" style="font-family: georgia, serif;">Logic Gates</span></em><span class="Apple-style-span" style="font-family: georgia, serif;"> and power switching circuits as they can be driven by digital logic levels.</span></div><h2 style="font-size: 12pt; font-weight: normal; text-align: left; text-decoration: underline;"><span class="Apple-style-span" style="font-family: georgia, serif;">MOSFET Summary</span></h2><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The </span><strong><span class="Apple-style-span" style="font-family: georgia, serif;">MOSFET</span></strong><span class="Apple-style-span" style="font-family: georgia, serif;"> has an extremely high input gate resistance and as such a easily damaged by static electricity if not carefully protected. MOSFET's are ideal for use as electronic switches or common-source amplifiers as their power consumption is very small. Typical applications for MOSFET's are in Microprocessors, Memories, Calculators and Logic Gates etc. Also, notice that the broken lines within the symbol indicates a normally "OFF" Enhancement type showing that "NO" current can flow through the channel when zero </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> voltage is applied and a continuous line within the symbol indicates a normally "ON" Depletion type showing that current "CAN" flow through the channel with zero </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> voltage. For P-Channel types the symbols are exactly the same for both types except that the arrow points outwards.</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="left" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">This can be summarised in the following switching table.</span></div><div align="left" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><table align="center" bgcolor="#f1f1f1" border="1" cellpadding="0" cellspacing="0" style="font-size: 11pt; text-align: center; text-decoration: none; width: 510px;"><tbody>
<tr align="center" bgcolor="#d3d3d3"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;" width="230"><span class="Apple-style-span" style="font-family: georgia, serif;">MOSFET type</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;" width="100"><span class="Apple-style-span" style="font-family: georgia, serif;">Vgs = +ve</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;" width="90"><span class="Apple-style-span" style="font-family: georgia, serif;">Vgs = 0</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;" width="90"><span class="Apple-style-span" style="font-family: georgia, serif;">Vgs = -ve</span></td></tr>
<tr align="center"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">N-Channel Depletion</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">ON</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">ON</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">OFF</span></td> </tr>
<tr align="center"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">N-Channel Enhancement</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">ON</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">OFF</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">OFF</span></td></tr>
<tr align="center"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">P-Channel Depletion</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">OFF</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">ON</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">ON</span></td></tr>
<tr align="center"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">P-Channel Enhancement</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">OFF</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">OFF</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">ON<br />
<br />
</span></td> </tr>
</tbody></table></span><span style="font-size: 12px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span></div><div><span style="font-size: 12px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span></div><div><span style="font-size: 12px;"></span><br />
<span style="font-size: 12px;"><h2 style="font-size: 12pt; font-weight: bold; text-align: left; text-decoration: underline;"><span class="Apple-style-span" style="font-family: georgia, serif;">The MOSFET as a Switch</span></h2><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">We saw previously, that the N-channel, Enhancement-mode MOSFET operates using a positive input voltage and has an extremely high input resistance (almost infinite) making it possible to interface with nearly any logic gate or driver capable of producing a positive output. Also, due to this very high input (</span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">Gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;">) resistance we can parallel together many different MOSFET's until we achieve the current handling limit required. While connecting together various MOSFET's may enable us to switch high current or high voltage loads, doing so becomes expensive and impractical in both components and circuit board space. To overcome this problem </span><b><span class="Apple-style-span" style="font-family: georgia, serif;">Power Field Effect Transistors</span></b><span class="Apple-style-span" style="font-family: georgia, serif;"> or </span><b><span class="Apple-style-span" style="font-family: georgia, serif;">Power FET's</span></b><span class="Apple-style-span" style="font-family: georgia, serif;"> where developed.</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">We now know that there are two main differences between FET's, Depletion-mode for JFET's and Enhancement-mode for MOSFET's and on this page we will look at using the Enhancement-mode MOSFET as a Switch.</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">By applying a suitable drive voltage to the </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">Gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> of an FET the resistance of the </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">Drain-Source</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> channel can be varied from an "OFF-resistance" of many hundreds of kΩ's, effectively an open circuit, to an "ON-resistance" of less than 1Ω, effectively a short circuit. We can also drive the MOSFET to turn "ON" fast or slow, or to pass high currents or low currents. This ability to turn the power MOSFET "ON" and "OFF" allows the device to be used as a very efficient switch with switching speeds much faster than standard bipolar junction transistors.</span></div><h3 style="font-size: 10pt; text-align: left; text-decoration: underline;"><span class="Apple-style-span" style="font-family: georgia, serif;">An example of using the MOSFET as a switch</span></h3><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="font-size: 9pt; text-align: left;"><tbody>
<tr><td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;" width="300"><span class="Apple-style-span" style="font-family: georgia, serif;"><img alt="MOSFET as a Switch" border="0" height="248" src="http://www.electronics-tutorials.ws/transistor/tran21.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="207" /></span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">In this circuit arrangement an Enhancement-mode N-channel MOSFET is being used to switch a simple lamp "ON" and "OFF" (could also be an LED). The gate input voltage </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">V</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">GS</span></sub></span><span class="Apple-style-span" style="font-family: georgia, serif;"> is taken to an appropriate positive voltage level to turn the device and the lamp either fully "ON", (</span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">V</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">GS</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;"> = +ve</span></span><span class="Apple-style-span" style="font-family: georgia, serif;">) or a zero voltage level to turn the device fully "OFF", (</span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">V</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">GS</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;"> = 0</span></span><span class="Apple-style-span" style="font-family: georgia, serif;">).<br />
If the resistive load of the lamp was to be replaced by an inductive load such as a coil or solenoid, a "Flywheel" diode would be required in parallel with the load to protect the MOSFET from any back-emf.</span></div></td></tr>
</tbody></table><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Above shows a very simple circuit for switching a resistive load such as a lamp or LED. But when using power MOSFET's to switch either inductive or capacitive loads some form of protection is required to prevent the MOSFET device from becoming damaged. Driving an inductive load has the opposite effect from driving a capacitive load. For example, a capacitor without an electrical charge is a short circuit, resulting in a high "inrush" of current and when we remove the voltage from an inductive load we have a large reverse voltage build up as the magnetic field collapses, resulting in an induced back-emf in the windings of the inductor.</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">For the power MOSFET to operate as an analogue switching device, it needs to be switched between its "Cut-off Region" where </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">V</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">GS</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;"> = 0</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> and its "Saturation Region" where </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">V</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">GS(on)</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;"> = +ve</span></span><span class="Apple-style-span" style="font-family: georgia, serif;">. The power dissipated in the MOSFET (</span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">P</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">D</span></sub></span><span class="Apple-style-span" style="font-family: georgia, serif;">) depends upon the current flowing through the channel </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">I</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">D</span></sub></span><span class="Apple-style-span" style="font-family: georgia, serif;"> at saturation and also the "ON-resistance" of the channel given as </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">DS(on)</span></sub></span><span class="Apple-style-span" style="font-family: georgia, serif;">. For example.</span></div><h3 style="font-size: 10pt; text-align: left; text-decoration: underline;"><span class="Apple-style-span" style="font-family: georgia, serif;">Example No1</span></h3><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Lets assume that the lamp is rated at 6v, 24W and is fully "ON" and the standard MOSFET has a channel "ON-resistance" ( </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">DS(on)</span></sub></span><span class="Apple-style-span" style="font-family: georgia, serif;"> ) value of 0.1ohms. Calculate the power dissipated in the MOSFET switch.</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><table bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="font-size: 9pt; text-align: left;"><tbody>
<tr><td align="left" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
The current flowing through the lamp is calculated as:</span></td></tr>
<tr align="center"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
<img alt="MOSFET Channel Current" border="0" height="52" src="http://www.electronics-tutorials.ws/transistor/tran23.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="437" /></span></td> </tr>
<tr><td align="left" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
Then the power dissipated in the MOSFET will be given as:</span></td> </tr>
<tr align="center"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
<img alt="MOSFET Power Dissipation" border="0" height="37" src="http://www.electronics-tutorials.ws/transistor/tran24.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="452" /></span></td> </tr>
</tbody></table><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">You may think, well so what!, but when using the MOSFET as a switch to control DC motors or high inrush current devices the "ON" channel resistance ( </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">DS(on)</span></sub></span><span class="Apple-style-span" style="font-family: georgia, serif;"> ) is very important. For example, MOSFET's that control DC motors, are subjected to a high in-rush current as the motor first begins to rotate. Then a high</span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">DS(on)</span></sub></span><span class="Apple-style-span" style="font-family: georgia, serif;"> channel resistance value would simply result in large amounts of power being dissipated within the MOSFET itself resulting in an excessive temperature rise, and which in turn could result in the MOSFET becoming very hot and damaged due to a thermal overload. But a low </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">DS(on)</span></sub></span><span class="Apple-style-span" style="font-family: georgia, serif;"> value on the other hand is also desirable to help reduce the effective saturation voltage ( </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">V</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">DS(sat)</span></sub></span><span class="Apple-style-span" style="font-family: georgia, serif;"> = </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">I</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">D</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;"> x R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">DS(on)</span></sub></span><span class="Apple-style-span" style="font-family: georgia, serif;"> ) across the MOSFET. When using MOSFET´s or any type of Field Effect Transistor for that matter as a switching device, it is always advisable to select ones that have a very low </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">DS(on)</span></sub></span><span class="Apple-style-span" style="font-family: georgia, serif;"> value or at least mount them onto a suitable heatsink to help reduce any thermal runaway and damage.</span></div><h2 style="font-size: 12pt; font-weight: normal; text-align: left; text-decoration: underline;"><span class="Apple-style-span" style="font-family: georgia, serif;">Power MOSFET Motor Control</span></h2><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Because of the extremely high input or </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">Gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> resistance that the MOSFET has, its very fast switching speeds and the ease at which they can be driven makes them ideal to interface with op-amps or standard logic gates. However, care must be taken to ensure that the </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate-source</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> input voltage is correctly chosen because when using the </span><strong><span class="Apple-style-span" style="font-family: georgia, serif;">MOSFET as a switch</span></strong><span class="Apple-style-span" style="font-family: georgia, serif;"> the device must obtain a low </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">DS(on)</span></sub></span><span class="Apple-style-span" style="font-family: georgia, serif;"> channel resistance in proportion to this input </span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> voltage. For example, do not apply a 12v signal if a 5v signal voltage is required. Power MOSFET´s can be used to control the movement of DC motors or brushless stepper motors directly from computer logic or Pulse-width Modulation (PWM) type controllers. As a DC motor offers high starting torque and which is also proportional to the armature current, MOSFET switches along with a PWM can be used as a very good speed controller that would provide smooth and quiet motor operation.</span></div><h3 style="font-size: 10pt; text-align: left; text-decoration: underline;"><span class="Apple-style-span" style="font-family: georgia, serif;">Simple Power MOSFET Motor Controller</span></h3><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><table align="center" bgcolor="fafafa" border="0" cellpadding="0" cellspacing="0" style="font-size: 9pt; text-align: left;"><tbody>
<tr align="center"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;" width="300"><span class="Apple-style-span" style="font-family: georgia, serif;"><img alt="MOSFET Switch" border="0" height="245" src="http://www.electronics-tutorials.ws/transistor/tran28.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="280" /></span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">As the motor load is inductive, a simple "Free-wheeling" diode is connected across the load to dissipate any back emf generated by the motor when the MOSFET turns it "OFF".<br />
The Zener diode is used to prevent excessive</span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span class="Apple-style-span" style="font-family: georgia, serif;">gate-source</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> input voltages.</span></div></td></tr>
</tbody></table></span></div><div><span style="font-size: 12px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span></div><div><span style="font-size: 12px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span></div><div><span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span><br />
<span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div class="MsoNormal" style="line-height: normal;"><span lang="EN-US"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Freddy Vallenilla R, EES, SECC1</span></span></span></div></span></div></span>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-58656252308432613772010-07-21T21:58:00.002-04:302010-07-25T10:23:42.155-04:30DIODES AND RECTIFIERS<span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span><br />
<div><span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><h1 style="font-size: 27px; font-weight: normal; letter-spacing: 2px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0.6em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Introduction</span></h1><div style="background-color: #ffce7b; border-bottom-color: rgb(255, 165, 0); border-bottom-style: solid; border-bottom-width: 1px; border-left-color: rgb(255, 165, 0); border-left-style: solid; border-left-width: 1px; border-right-color: rgb(255, 165, 0); border-right-style: solid; border-right-width: 1px; border-top-color: rgb(255, 165, 0); border-top-style: solid; border-top-width: 1px; font-weight: bold; line-height: 18px; margin-bottom: 1em; margin-left: 0px; margin-right: 0px; margin-top: 2em; padding-bottom: 0.5em; padding-left: 1em; padding-right: 1em; padding-top: 0.5em; vertical-align: middle;"><span style="font-weight: normal;"><u><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></u></span></div><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Rectifier" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">diode</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> is an electrical device allowing current to move through it in one direction with far greater ease than in the other. The most common kind of diode in modern circuit design is the </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">semiconductor</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> diode, although other diode technologies exist. Semiconductor diodes are symbolized in schematic diagrams such as Figure below. The term "diode" is customarily reserved for small signal devices, I ≤ 1 A. The term </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">rectifier</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> is used for power devices, I > 1 A.</span></div><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03246.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03246.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Semiconductor diode schematic symbol: Arrows indicate the direction of electron current flow.</span></i></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">When placed in a simple battery-lamp circuit, the diode will either allow or prevent current through the lamp, depending on the polarity of the applied voltage. (Figure below)</span></div><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03247.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03247.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diode operation: (a) Current flow is permitted; the diode is forward biased. (b) Current flow is prohibited; the diode is reversed biased.</span></i></div><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Forward bias" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Reverse bias" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Bias, diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">When the polarity of the battery is such that electrons are allowed to flow through the diode, the diode is said to be </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">forward-biased</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">. Conversely, when the battery is "backward" and the diode blocks current, the diode is said to be </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">reverse-biased</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">. A diode may be thought of as like a switch: "closed" when forward-biased and "open" when reverse-biased.</span></div><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Conventional flow" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Electron flow" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Flow, electron vs. conventional" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Oddly enough, the direction of the diode symbol's "arrowhead" points </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">against</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> the direction of electron flow. This is because the diode symbol was invented by engineers, who predominantly use </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">conventional flow</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> notation in their schematics, showing current as a flow of charge from the positive (+) side of the voltage source to the negative (-). This convention holds true for all semiconductor symbols possessing "arrowheads:" the arrow points in the permitted direction of conventional flow, and against the permitted direction of electron flow.</span></div><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Check valve" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a check""="" href="" name="Valve, " style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diode behavior is analogous to the behavior of a hydraulic device called a </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">check valve</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">. A check valve allows fluid flow through it in only one direction as in Figure below.</span></div><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03248.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="75" src="http://sub.allaboutcircuits.com/images/03248.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Hydraulic check valve analogy: (a) Electron current flow permitted. (b) Current flow prohibited.</span></i></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Check valves are essentially pressure-operated devices: they open and allow flow if the pressure across them is of the correct "polarity" to open the gate (in the analogy shown, greater fluid pressure on the right than on the left). If the pressure is of the opposite "polarity," the pressure difference across the check valve will close and hold the gate so that no flow occurs.</span></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Like check valves, diodes are essentially "pressure-" operated (voltage-operated) devices. The essential difference between forward-bias and reverse-bias is the polarity of the voltage dropped across the diode. Let's take a closer look at the simple battery-diode-lamp circuit shown earlier, this time investigating voltage drops across the various components in Figure below.</span></div><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03249.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="66" src="http://sub.allaboutcircuits.com/images/03249.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diode circuit voltage measurements: (a) Forward biased. (b) Reverse biased.</span></i></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A forward-biased diode conducts current and drops a small voltage across it, leaving most of the battery voltage dropped across the lamp. If the battery's polarity is reversed, the diode becomes reverse-biased, and drops </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">all</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> of the battery's voltage leaving none for the lamp. If we consider the diode to be a self-actuating switch (closed in the forward-bias mode and open in the reverse-bias mode), this behavior makes sense. The most substantial difference is that the diode drops a lot more voltage when conducting than the average mechanical switch (0.7 volts versus tens of millivolts).</span></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">This forward-bias voltage drop exhibited by the diode is due to the action of the depletion region formed by the P-N junction under the influence of an applied voltage. If no voltage applied is across a semiconductor diode, a thin depletion region exists around the region of the P-N junction, preventing current flow. (Figure below (a)) The depletion region is almost devoid of available charge carriers, and acts as an insulator:</span></div><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03250.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="117" src="http://sub.allaboutcircuits.com/images/03250.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diode representations: PN-junction model, schematic symbol, physical part.</span></i></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The schematic symbol of the diode is shown in Figure above (b) such that the anode (pointing end) corresponds to the P-type semiconductor at (a). The cathode bar, non-pointing end, at (b) corresponds to the N-type material at (a). Also note that the cathode stripe on the physical part (c) corresponds to the cathode on the symbol.</span></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">If a reverse-biasing voltage is applied across the P-N junction, this depletion region expands, further resisting any current through it. (Figure below)</span></div><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03251.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="86" src="http://sub.allaboutcircuits.com/images/03251.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Depletion region expands with reverse bias.</span></i></div><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Forward voltage, diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Voltage, forward" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Conversely, if a forward-biasing voltage is applied across the P-N junction, the depletion region collapses becoming thinner. The diode becomes less resistive to current through it. In order for a sustained current to go through the diode; though, the depletion region must be fully collapsed by the applied voltage. This takes a certain minimum voltage to accomplish, called the </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">forward voltage</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> as illustrated in Figure </span><a href="http://www.allaboutcircuits.com/vol_3/chpt_3/1.html#03252.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-decoration: underline;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">below</span></span></a><span class="Apple-style-span" style="font-family: georgia, serif;">.</span></div><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03252.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="72" src="http://sub.allaboutcircuits.com/images/03252.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Inceasing forward bias from (a) to (b) decreases depletion region thickness.</span></i></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">For silicon diodes, the typical forward voltage is 0.7 volts, nominal. For germanium diodes, the forward voltage is only 0.3 volts. The chemical constituency of the P-N junction comprising the diode accounts for its nominal forward voltage figure, which is why silicon and germanium diodes have such different forward voltages. Forward voltage drop remains approximately constant for a wide range of diode currents, meaning that diode voltage drop is not like that of a resistor or even a normal (closed) switch. For most simplified circuit analysis, the voltage drop across a conducting diode may be considered constant at the nominal figure and not related to the amount of current.</span></div><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Diode equation, the" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Equation, diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="DioEqu" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Actually, forward voltage drop is more complex. An equation describes the exact current through a diode, given the voltage dropped across the junction, the temperature of the junction, and several physical constants. It is commonly known as the </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">diode equation</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">:</span></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/13047.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Thermal voltage, diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The term kT/q describes the voltage produced within the P-N junction due to the action of temperature, and is called the </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">thermal voltage</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">, or V</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">t</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">of the junction. At room temperature, this is about 26 millivolts. Knowing this, and assuming a "nonideality" coefficient of 1, we may simplify the diode equation and re-write it as such:</span></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/13048.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">You need not be familiar with the "diode equation" to analyze simple diode circuits. Just understand that the voltage dropped across a current-conducting diode </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">does</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> change with the amount of current going through it, but that this change is fairly small over a wide range of currents. This is why many textbooks simply say the voltage drop across a conducting, semiconductor diode remains constant at 0.7 volts for silicon and 0.3 volts for germanium. However, some circuits intentionally make use of the P-N junction's inherent exponential current/voltage relationship and thus can only be understood in the context of this equation. Also, since temperature is a factor in the diode equation, a forward-biased P-N junction may also be used as a temperature-sensing device, and thus can only be understood if one has a conceptual grasp on this mathematical relationship.</span></div><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Leakage current, diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Breakdown, diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="PIV rating, diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Diode PIV rating" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Reverse voltage rating, diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A reverse-biased diode prevents current from going through it, due to the expanded depletion region. In actuality, a very small amount of current can and does go through a reverse-biased diode, called the </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">leakage current</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">, but it can be ignored for most purposes. The ability of a diode to withstand reverse-bias voltages is limited, as it is for any insulator. If the applied reverse-bias voltage becomes too great, the diode will experience a condition known as </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">breakdown</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> (Figure below), which is usually destructive. A diode's maximum reverse-bias voltage rating is known as the </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Peak Inverse Voltage</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">, or </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">PIV</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">, and may be obtained from the manufacturer. Like forward voltage, the PIV rating of a diode varies with temperature, except that PIV </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">increases</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> with increased temperature and </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">decreases</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> as the diode becomes cooler -- exactly opposite that of forward voltage.</span></div><span style="line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03253.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03253.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diode curve: showing knee at 0.7 V forward bias for Si, and reverse breakdown.</span></i></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Typically, the PIV rating of a generic "rectifier" diode is at least 50 volts at room temperature. Diodes with PIV ratings in the many thousands of volts are available for modest prices.</span></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div style="line-height: 18px; margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></div><h1 style="font-size: 27px; font-weight: normal; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0.6em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Meter check of a diode</span></h1><div><div style="background-color: #ffce7b; border-bottom-color: rgb(255, 165, 0); border-bottom-style: solid; border-bottom-width: 1px; border-left-color: rgb(255, 165, 0); border-left-style: solid; border-left-width: 1px; border-right-color: rgb(255, 165, 0); border-right-style: solid; border-right-width: 1px; border-top-color: rgb(255, 165, 0); border-top-style: solid; border-top-width: 1px; font-weight: bold; margin-bottom: 1em; margin-left: 0px; margin-right: 0px; margin-top: 2em; padding-bottom: 0.5em; padding-left: 1em; padding-right: 1em; padding-top: 0.5em; text-align: center; vertical-align: middle;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Being able to determine the polarity (cathode versus anode) and basic functionality of a diode is a very important skill for the electronics hobbyist or technician to have. Since we know that a diode is essentially nothing more than a one-way valve for electricity, it makes sense we should be able to verify its one-way nature using a DC (battery-powered) ohmmeter as in Figure below. Connected one way across the diode, the meter should show a very low resistance at (a). Connected the other way across the diode, it should show a very high resistance at (b) ("OL" on some digital meter models).</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03254.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="70" src="http://sub.allaboutcircuits.com/images/03254.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Determination of diode polarity: (a) Low resistance indicates forward bias, black lead is cathode and red lead anode (for most meters) (b) Reversing leads shows high resistance indicating reverse bias.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Of course, to determine which end of the diode is the cathode and which is the anode, you must know with certainty which test lead of the meter is positive (+) and which is negative (-) when set to the "resistance" or "Ω" function. With most digital multimeters I've seen, the red lead becomes positive and the black lead negative when set to measure resistance, in accordance with standard electronics color-code convention. However, this is not guaranteed for all meters. Many analog multimeters, for example, actually make their black leads positive (+) and their red leads negative (-) when switched to the "resistance" function, because it is easier to manufacture it that way!</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">One problem with using an ohmmeter to check a diode is that the readings obtained only have qualitative value, not quantitative. In other words, an ohmmeter only tells you which way the diode conducts; the low-value resistance indication obtained while conducting is useless. If an ohmmeter shows a value of "1.73 ohms" while forward-biasing a diode, that figure of 1.73 Ω doesn't represent any real-world quantity useful to us as technicians or circuit designers. It neither represents the forward voltage drop nor any "bulk" resistance in the semiconductor material of the diode itself, but rather is a figure dependent upon both quantities and will vary substantially with the particular ohmmeter used to take the reading.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Diode check, meter function" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">For this reason, some digital multimeter manufacturers equip their meters with a special "diode check" function which displays the actual forward voltage drop of the diode in volts, rather than a "resistance" figure in ohms. These meters work by forcing a small current through the diode and measuring the voltage dropped between the two test leads. (Figure below)</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="142" src="http://sub.allaboutcircuits.com/images/03256.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Meter with a "Diode check" function displays the forward voltage drop of 0.548 volts instead of a low resistance.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The forward voltage reading obtained with such a meter will typically be less than the "normal" drop of 0.7 volts for silicon and 0.3 volts for germanium, because the current provided by the meter is of trivial proportions. If a multimeter with diode-check function isn't available, or you would like to measure a diode's forward voltage drop at some non-trivial current, the circuit of Figure below may be constructed using a battery, resistor, and voltmeter</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03257.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="95" src="http://sub.allaboutcircuits.com/images/03257.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Measuring forward voltage of a diode without"diode check" meter function: (a) Schematic diagram. (b) Pictorial diagram.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Connecting the diode backwards to this testing circuit will simply result in the voltmeter indicating the full voltage of the battery.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">If this circuit were designed to provide a constant or nearly constant current through the diode despite changes in forward voltage drop, it could be used as the basis of a temperature-measurement instrument, the voltage measured across the diode being inversely proportional to diode junction temperature. Of course, diode current should be kept to a minimum to avoid self-heating (the diode dissipating substantial amounts of heat energy), which would interfere with temperature measurement.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Beware that some digital multimeters equipped with a "diode check" function may output a very low test voltage (less than 0.3 volts) when set to the regular "resistance" (Ω) function: too low to fully collapse the depletion region of a PN junction. The philosophy here is that the "diode check" function is to be used for testing semiconductor devices, and the "resistance" function for anything else. By using a very low test voltage to measure resistance, it is easier for a technician to measure the resistance of non-semiconductor components connected to semiconductor components, since the semiconductor component junctions will not become forward-biased with such low voltages.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Printed circuit board" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="PCB" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Consider the example of a resistor and diode connected in parallel, soldered in place on a printed circuit board (PCB). Normally, one would have to unsolder the resistor from the circuit (disconnect it from all other components) before measuring its resistance, otherwise any parallel-connected components would affect the reading obtained. When using a multimeter which outputs a very low test voltage to the probes in the "resistance" function mode, the diode's PN junction will not have enough voltage impressed across it to become forward-biased, and will only pass negligible current. Consequently, the meter "sees" the diode as an open (no continuity), and only registers the resistor's resistance. (Figure below)</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03329.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="101" src="http://sub.allaboutcircuits.com/images/03329.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Ohmmeter equipped with a low test voltage (<0.7 V) does not see diodes allowing it to measure parallel resistors.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">If such an ohmmeter were used to test a diode, it would indicate a very high resistance (many mega-ohms) even if connected to the diode in the "correct" (forward-biased) direction. (Figure below)</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03330.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="138" src="http://sub.allaboutcircuits.com/images/03330.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Ohmmeter equipped with a low test voltage, too low to forward bias diodes, does not see diodes.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Reverse voltage strength of a diode is not as easily tested, because exceeding a normal diode's PIV usually results in destruction of the diode. Special types of diodes, though, which are designed to "break down" in reverse-bias mode without damage (called </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">zener diodes</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">), which are tested with the same voltage source / resistor / voltmeter circuit, provided that the voltage source is of high enough value to force the diode into its breakdown region. More on this subject in a later section of this chapter.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span style="line-height: 18px;"></span></span></div><h1 style="font-size: 27px; font-weight: normal; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0.6em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diode ratings</span></h1><div><div style="background-color: #ffce7b; border-bottom-color: rgb(255, 165, 0); border-bottom-style: solid; border-bottom-width: 1px; border-left-color: rgb(255, 165, 0); border-left-style: solid; border-left-width: 1px; border-right-color: rgb(255, 165, 0); border-right-style: solid; border-right-width: 1px; border-top-color: rgb(255, 165, 0); border-top-style: solid; border-top-width: 1px; font-weight: bold; margin-bottom: 1em; margin-left: 0px; margin-right: 0px; margin-top: 2em; padding-bottom: 0.5em; padding-left: 1em; padding-right: 1em; padding-top: 0.5em; text-align: center; vertical-align: middle;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Datasheet, component" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">In addition to forward voltage drop (V</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">f</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">) and peak inverse voltage (PIV), there are many other ratings of diodes important to circuit design and component selection. Semiconductor manufacturers provide detailed specifications on their products -- diodes included -- in publications known as </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">datasheets</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">. Datasheets for a wide variety of semiconductor components may be found in reference books and on the internet. I prefer the internet as a source of component specifications because all the data obtained from manufacturer websites are up-to-date.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A typical diode datasheet will contain figures for the following parameters:</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Maximum repetitive reverse voltage</span></u><span class="Apple-style-span" style="font-family: georgia, serif;"> = V</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">RRM</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">, the maximum amount of voltage the diode can withstand in reverse-bias mode, in repeated pulses. Ideally, this figure would be infinite.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Maximum DC reverse voltage</span></u><span class="Apple-style-span" style="font-family: georgia, serif;"> = V</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;"> or V</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">DC</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">, the maximum amount of voltage the diode can withstand in reverse-bias mode on a continual basis. Ideally, this figure would be infinite.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Maximum forward voltage</span></u><span class="Apple-style-span" style="font-family: georgia, serif;"> = V</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">F</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">, usually specified at the diode's rated forward current. Ideally, this figure would be zero: the diode providing no opposition whatsoever to forward current. In reality, the forward voltage is described by the "diode equation."</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Maximum (average) forward current</span></u><span class="Apple-style-span" style="font-family: georgia, serif;"> = I</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">F(AV)</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">, the maximum average amount of current the diode is able to conduct in forward bias mode. This is fundamentally a thermal limitation: how much heat can the PN junction handle, given that dissipation power is equal to current (I) multiplied by voltage (V or E) and forward voltage is dependent upon both current and junction temperature. Ideally, this figure would be infinite.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Maximum (peak or surge) forward current</span></u><span class="Apple-style-span" style="font-family: georgia, serif;"> = I</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">FSM</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;"> or i</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">f(surge)</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">, the maximum peak amount of current the diode is able to conduct in forward bias mode. Again, this rating is limited by the diode junction's thermal capacity, and is usually much higher than the average current rating due to thermal inertia (the fact that it takes a finite amount of time for the diode to reach maximum temperature for a given current). Ideally, this figure would be infinite.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Maximum total dissipation</span></u><span class="Apple-style-span" style="font-family: georgia, serif;"> = P</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">D</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">, the amount of power (in watts) allowable for the diode to dissipate, given the dissipation (P=IE) of diode current multiplied by diode voltage drop, and also the dissipation (P=I</span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">2</span></sup><span class="Apple-style-span" style="font-family: georgia, serif;">R) of diode current squared multiplied by bulk resistance. Fundamentally limited by the diode's thermal capacity (ability to tolerate high temperatures).</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Operating junction temperature</span></u><span class="Apple-style-span" style="font-family: georgia, serif;"> = T</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">J</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">, the maximum allowable temperature for the diode's PN junction, usually given in degrees Celsius (</span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">o</span></sup><span class="Apple-style-span" style="font-family: georgia, serif;">C). Heat is the "Achilles' heel" of semiconductor devices: they </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">must</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> be kept cool to function properly and give long service life.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Storage temperature range</span></u><span class="Apple-style-span" style="font-family: georgia, serif;"> = T</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">STG</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">, the range of allowable temperatures for storing a diode (unpowered). Sometimes given in conjunction with operating junction temperature (T</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">J</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">), because the maximum storage temperature and the maximum operating temperature ratings are often identical. If anything, though, maximum storage temperature rating will be greater than the maximum operating temperature rating.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Thermal resistance</span></u><span class="Apple-style-span" style="font-family: georgia, serif;"> = R(Θ), the temperature difference between junction and outside air (R(Θ)</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">JA</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">) or between junction and leads (R(Θ)</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">JL</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">) for a given power dissipation. Expressed in units of degrees Celsius per watt (</span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">o</span></sup><span class="Apple-style-span" style="font-family: georgia, serif;">C/W). Ideally, this figure would be zero, meaning that the diode package was a perfect thermal conductor and radiator, able to transfer all heat energy from the junction to the outside air (or to the leads) with no difference in temperature across the thickness of the diode package. A high thermal resistance means that the diode will build up excessive temperature at the junction (where its critical) despite best efforts at cooling the outside of the diode, and thus will limit its maximum power dissipation.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Leakage current, diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Current, diode leakage" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Diode leakage current" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Maximum reverse current</span></u><span class="Apple-style-span" style="font-family: georgia, serif;"> = I</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">, the amount of current through the diode in </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">reverse-bias</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> operation, with the maximum rated inverse voltage applied (V</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">DC</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">). Sometimes referred to as </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">leakage current</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">. Ideally, this figure would be zero, as a perfect diode would block all current when reverse-biased. In reality, it is very small compared to the maximum forward current.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Capacitance, diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Junction capacitance, diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Diode junction capacitance" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Typical junction capacitance</span></u><span class="Apple-style-span" style="font-family: georgia, serif;"> = C</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">J</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">, the typical amount of capacitance intrinsic to the junction, due to the depletion region acting as a dielectric separating the anode and cathode connections. This is usually a very small figure, measured in the range of picofarads (pF).</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Reverse recovery time, diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Switching time, diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Commutation time, diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Time, diode switching" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Reverse recovery time</span></u><span class="Apple-style-span" style="font-family: georgia, serif;"> = t</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">rr</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">, the amount of time it takes for a diode to "turn off" when the voltage across it alternates from forward-bias to reverse-bias polarity. Ideally, this figure would be zero: the diode halting conduction </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">immediately</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> upon polarity reversal. For a typical rectifier diode, reverse recovery time is in the range of tens of microseconds; for a "fast switching" diode, it may only be a few nanoseconds.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Most of these parameters vary with temperature or other operating conditions, and so a single figure fails to fully describe any given rating. Therefore, manufacturers provide graphs of component ratings plotted against other variables (such as temperature), so that the circuit designer has a better idea of what the device is capable of.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></div><h1 style="font-size: 27px; font-weight: normal; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0.6em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Rectifier circuits</span></h1><div><div style="background-color: #ffce7b; border-bottom-color: rgb(255, 165, 0); border-bottom-style: solid; border-bottom-width: 1px; border-left-color: rgb(255, 165, 0); border-left-style: solid; border-left-width: 1px; border-right-color: rgb(255, 165, 0); border-right-style: solid; border-right-width: 1px; border-top-color: rgb(255, 165, 0); border-top-style: solid; border-top-width: 1px; font-weight: bold; margin-bottom: 1em; margin-left: 0px; margin-right: 0px; margin-top: 2em; padding-bottom: 0.5em; padding-left: 1em; padding-right: 1em; padding-top: 0.5em; text-align: center; vertical-align: middle;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Rectifier circuit" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Rectifier circuit, half-wave" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Half-wave rectifier circuit" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="half-W-R" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Now we come to the most popular application of the diode: </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">rectification</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">. Simply defined, rectification is the conversion of alternating current (AC) to direct current (DC). This involves a device that only allows one-way flow of electrons. As we have seen, this is exactly what a semiconductor diode does. The simplest kind of rectifier circuit is the </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">half-wave</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> rectifier. It only allows one half of an AC waveform to pass through to the load. (Figure below)</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03258.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="42" src="http://sub.allaboutcircuits.com/images/03258.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Half-wave rectifier circuit.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">For most power applications, half-wave rectification is insufficient for the task. The harmonic content of the rectifier's output waveform is very large and consequently difficult to filter. Furthermore, the AC power source only supplies power to the load one half every full cycle, meaning that half of its capacity is unused. Half-wave rectification is, however, a very simple way to reduce power to a resistive load. Some two-position lamp dimmer switches apply full AC power to the lamp filament for "full" brightness and then half-wave rectify it for a lesser light output. (Figure below)</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03259.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03259.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Half-wave rectifier application: Two level lamp dimmer.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">In the "Dim" switch position, the incandescent lamp receives approximately one-half the power it would normally receive operating on full-wave AC. Because the half-wave rectified power pulses far more rapidly than the filament has time to heat up and cool down, the lamp does not blink. Instead, its filament merely operates at a lesser temperature than normal, providing less light output. This principle of "pulsing" power rapidly to a slow-responding load device to control the electrical power sent to it is common in the world of industrial electronics. Since the controlling device (the diode, in this case) is either fully conducting or fully nonconducting at any given time, it dissipates little heat energy while controlling load power, making this method of power control very energy-efficient. This circuit is perhaps the crudest possible method of pulsing power to a load, but it suffices as a proof-of-concept application.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Rectifier circuit, full-wave" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Full-wave rectifier circuit" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Center-tap rectifier circuit" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">If we need to rectify AC power to obtain the full use of </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">both</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> half-cycles of the sine wave, a different rectifier circuit configuration must be used. Such a circuit is called a </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">full-wave</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> rectifier. One kind of full-wave rectifier, called the </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">center-tap</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> design, uses a transformer with a center-tapped secondary winding and two diodes, as in Figure below.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03260.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="52" src="http://sub.allaboutcircuits.com/images/03260.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Full-wave rectifier, center-tapped design.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">This circuit's operation is easily understood one half-cycle at a time. Consider the first half-cycle, when the source voltage polarity is positive (+) on top and negative (-) on bottom. At this time, only the top diode is conducting; the bottom diode is blocking current, and the load "sees" the first half of the sine wave, positive on top and negative on bottom. Only the top half of the transformer's secondary winding carries current during this half-cycle as in Figure below.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03261.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03261.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Full-wave center-tap rectifier: Top half of secondary winding conducts during positive half-cycle of input, delivering positive half-cycle to load..</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">During the next half-cycle, the AC polarity reverses. Now, the other diode and the other half of the transformer's secondary winding carry current while the portions of the circuit formerly carrying current during the last half-cycle sit idle. The load still "sees" half of a sine wave, of the same polarity as before: positive on top and negative on bottom. (Figure below)</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03262.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="61" src="http://sub.allaboutcircuits.com/images/03262.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Full-wave center-tap rectifier: During negative input half-cycle, bottom half of secondary winding conducts, delivering a positive half-cycle to the load.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">One disadvantage of this full-wave rectifier design is the necessity of a transformer with a center-tapped secondary winding. If the circuit in question is one of high power, the size and expense of a suitable transformer is significant. Consequently, the center-tap rectifier design is only seen in low-power applications.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The full-wave center-tapped rectifier polarity at the load may be reversed by changing the direction of the diodes. Furthermore, the reversed diodes can be paralleled with an existing positive-output rectifier. The result is dual-polarity full-wave center-tapped rectifier in Figure below. Note that the connectivity of the diodes themselves is the same configuration as a bridge.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03444.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="60" src="http://sub.allaboutcircuits.com/images/03444.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Dual polarity full-wave center tap rectifier</span></i></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Rectifier circuit, full-wave" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Full-wave rectifier circuit" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Bridge rectifier circuit" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Another, more popular full-wave rectifier design exists, and it is built around a four-diode bridge configuration. For obvious reasons, this design is called a </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">full-wave bridge</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">. (Figure below)</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03263.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="57" src="http://sub.allaboutcircuits.com/images/03263.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Full-wave bridge rectifier.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Current directions for the full-wave bridge rectifier circuit are as shown in Figure below for positive half-cycle and Figure below for negative half-cycles of the AC source waveform. Note that regardless of the polarity of the input, the current flows in the same direction through the load. That is, the negative half-cycle of source is a positive half-cycle at the load. The current flow is through two diodes in series for both polarities. Thus, two diode drops of the source voltage are lost (0.7·2=1.4 V for Si) in the diodes. This is a disadvantage compared with a full-wave center-tap design. This disadvantage is only a problem in very low voltage power supplies.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03264.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="78" src="http://sub.allaboutcircuits.com/images/03264.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Full-wave bridge rectifier: Electron flow for positive half-cycles.</span></i></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03265.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="78" src="http://sub.allaboutcircuits.com/images/03265.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Full-wave bridge rectifier: Electron flow for negative half=cycles.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Remembering the proper layout of diodes in a full-wave bridge rectifier circuit can often be frustrating to the new student of electronics. I've found that an alternative representation of this circuit is easier both to remember and to comprehend. It's the exact same circuit, except all diodes are drawn in a horizontal attitude, all "pointing" the same direction. (Figure below)</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03266.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="62" src="http://sub.allaboutcircuits.com/images/03266.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Alternative layout style for Full-wave bridge rectifier.</span></i></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Bridge rectifier circuit, polyphase" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Polyphase bridge rectifier circuit" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Three-phase bridge rectifier circuit" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">One advantage of remembering this layout for a bridge rectifier circuit is that it expands easily into a polyphase version in Figure below.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03267.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="77" src="http://sub.allaboutcircuits.com/images/03267.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Three-phase full-wave bridge rectifier circuit.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Each three-phase line connects between a pair of diodes: one to route power to the positive (+) side of the load, and the other to route power to the negative (-) side of the load. Polyphase systems with more than three phases are easily accommodated into a bridge rectifier scheme. Take for instance the six-phase bridge rectifier circuit in Figure below.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03268.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="114" src="http://sub.allaboutcircuits.com/images/03268.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Six-phase full-wave bridge rectifier circuit.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">When polyphase AC is rectified, the phase-shifted pulses overlap each other to produce a DC output that is much "smoother" (has less AC content) than that produced by the rectification of single-phase AC. This is a decided advantage in high-power rectifier circuits, where the sheer physical size of filtering components would be prohibitive but low-noise DC power must be obtained. The diagram in Figure below shows the full-wave rectification of three-phase AC.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03269.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="85" src="http://sub.allaboutcircuits.com/images/03269.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Three-phase AC and 3-phase full-wave rectifier output.</span></i></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Ripple voltage" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Voltage, ripple" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">In any case of rectification -- single-phase or polyphase -- the amount of AC voltage mixed with the rectifier's DC output is called </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">ripple voltage</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">. In most cases, since "pure" DC is the desired goal, ripple voltage is undesirable. If the power levels are not too great, filtering networks may be employed to reduce the amount of ripple in the output voltage.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Sometimes, the method of rectification is referred to by counting the number of DC "pulses" output for every 360</span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">o</span></sup><span class="Apple-style-span" style="font-family: georgia, serif;"> of electrical "rotation." A single-phase, half-wave rectifier circuit, then, would be called a </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">1-pulse</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> rectifier, because it produces a single pulse during the time of one complete cycle (360</span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">o</span></sup><span class="Apple-style-span" style="font-family: georgia, serif;">) of the AC waveform. A single-phase, full-wave rectifier (regardless of design, center-tap or bridge) would be called a </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">2-pulse</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> rectifier, because it outputs two pulses of DC during one AC cycle's worth of time. A three-phase full-wave rectifier would be called a </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">6-pulse</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> unit.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Modern electrical engineering convention further describes the function of a rectifier circuit by using a three-field notation of </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">phases</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">, </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">ways</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">, and number of </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">pulses</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">. A single-phase, half-wave rectifier circuit is given the somewhat cryptic designation of 1Ph1W1P (1 phase, 1 way, 1 pulse), meaning that the AC supply voltage is single-phase, that current on each phase of the AC supply lines moves in only one direction (way), and that there is a single pulse of DC produced for every 360</span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">o</span></sup><span class="Apple-style-span" style="font-family: georgia, serif;"> of electrical rotation. A single-phase, full-wave, center-tap rectifier circuit would be designated as 1Ph1W2P in this notational system: 1 phase, 1 way or direction of current in each winding half, and 2 pulses or output voltage per cycle. A single-phase, full-wave, bridge rectifier would be designated as 1Ph2W2P: the same as for the center-tap design, except current can go </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">both</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> ways through the AC lines instead of just one way. The three-phase bridge rectifier circuit shown earlier would be called a 3Ph2W6P rectifier.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Is it possible to obtain more pulses than twice the number of phases in a rectifier circuit? The answer to this question is yes: especially in polyphase circuits. Through the creative use of transformers, sets of full-wave rectifiers may be paralleled in such a way that more than six pulses of DC are produced for three phases of AC. A 30</span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">o</span></sup><span class="Apple-style-span" style="font-family: georgia, serif;"> phase shift is introduced from primary to secondary of a three-phase transformer when the winding configurations are not of the same type. In other words, a transformer connected either Y-Δ or Δ-Y will exhibit this 30</span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">o</span></sup><span class="Apple-style-span" style="font-family: georgia, serif;"> phase shift, while a transformer connected Y-Y or Δ-Δ will not. This phenomenon may be exploited by having one transformer connected Y-Y feed a bridge rectifier, and have another transformer connected Y-Δ feed a second bridge rectifier, then parallel the DC outputs of both rectifiers. (Figure below) Since the ripple voltage waveforms of the two rectifiers' outputs are phase-shifted 30</span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">o</span></sup><span class="Apple-style-span" style="font-family: georgia, serif;"> from one another, their superposition results in less ripple than either rectifier output considered separately: 12 pulses per 360</span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">o</span></sup><span class="Apple-style-span" style="font-family: georgia, serif;"> instead of just six:</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03270.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="105" src="http://sub.allaboutcircuits.com/images/03270.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Polyphase rectifier circuit: 3-phase 2-way 12-pulse (3Ph2W12P)</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span style="font-style: normal;"></span></span></i></div><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></i><br />
<i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><h1 style="font-size: 27px; font-weight: normal; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0.6em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Peak detector</span></h1><div><div style="background-color: #ffce7b; border-bottom-color: rgb(255, 165, 0); border-bottom-style: solid; border-bottom-width: 1px; border-left-color: rgb(255, 165, 0); border-left-style: solid; border-left-width: 1px; border-right-color: rgb(255, 165, 0); border-right-style: solid; border-right-width: 1px; border-top-color: rgb(255, 165, 0); border-top-style: solid; border-top-width: 1px; font-weight: bold; margin-bottom: 1em; margin-left: 0px; margin-right: 0px; margin-top: 2em; padding-bottom: 0.5em; padding-left: 1em; padding-right: 1em; padding-top: 0.5em; text-align: center; vertical-align: middle;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Peak detector" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">peak detector</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> is a series connection of a diode and a capacitor outputting a DC voltage equal to the peak value of the applied AC signal. The circuit is shown in Figure below with the corresponding SPICE net list. An AC voltage source applied to the peak detector, charges the capacitor to the peak of the input. The diode conducts positive "half cycles," charging the capacitor to the waveform peak. When the input waveform falls below the DC "peak" stored on the capacitor, the diode is reverse biased, blocking current flow from capacitor back to the source. Thus, the capacitor retains the peak value even as the waveform drops to zero. Another view of the peak detector is that it is the same as a half-wave rectifier with a filter capacitor added to the output.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03441.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<table border="1" style="background-color: lightcyan; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><tbody style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03441.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><pre style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">*SPICE 03441.eps C1 2 0 0.1u R1 1 3 1.0k V1 1 0 SIN(0 5 1k) D1 3 2 diode .model diode d .tran 0.01m 50mm .end </span></pre></td></tr>
</tbody></table><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Peak detector: Diode conducts on positive half cycles charging capacitor to the peak voltage (less diode forward drop).</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">It takes a few cycles for the capacitor to charge to the peak as in Figure below due to the series resistance (RC "time constant"). Why does the capacitor not charge all the way to 5 V? It would charge to 5 V if an "ideal diode" were obtainable. However, the silicon diode has a forward voltage drop of 0.7 V which subtracts from the 5 V peak of the input.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="23027.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/23027.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Peak detector: Capacitor charges to peak within a few cycles.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The circuit in Figure above could represent a DC power supply based on a half-wave rectifier. The resistance would be a few Ohms instead of 1 kΩ due to a transformer secondary winding replacing the voltage source and resistor. A larger "filter" capacitor would be used. A power supply based on a 60 Hz source with a filter of a few hundred µF could supply up to 100 mA. Half-wave supplies seldom supply more due to the difficulty of filtering a half-wave.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></div><h1 style="font-size: 27px; font-weight: normal; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0.6em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Clipper circuits</span></h1><div><div style="background-color: #ffce7b; border-bottom-color: rgb(255, 165, 0); border-bottom-style: solid; border-bottom-width: 1px; border-left-color: rgb(255, 165, 0); border-left-style: solid; border-left-width: 1px; border-right-color: rgb(255, 165, 0); border-right-style: solid; border-right-width: 1px; border-top-color: rgb(255, 165, 0); border-top-style: solid; border-top-width: 1px; font-weight: bold; margin-bottom: 1em; margin-left: 0px; margin-right: 0px; margin-top: 2em; padding-bottom: 0.5em; padding-left: 1em; padding-right: 1em; padding-top: 0.5em; text-align: center; vertical-align: middle;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Clipper circuit" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Slicer circuit" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A circuit which removes the peak of a waveform is known as a </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">clipper</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">. A negative clipper is shown in Figure below. This schematic diagram was produced with Xcircuit schematic capture program. Xcircuit produced the SPICE net list Figure below, except for the second, and next to last pair of lines which were inserted with a text editor.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03437.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<table border="1" style="background-color: lightcyan; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><tbody style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03437.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><pre style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">*SPICE 03437.eps * A K ModelName D1 0 2 diode R1 2 1 1.0k V1 1 0 SIN(0 5 1k) .model diode d .tran .05m 3m .end </span></pre></td></tr>
</tbody></table><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Clipper: clips negative peak at -0.7 V.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">During the positive half cycle of the 5 V peak input, the diode is reversed biased. The diode does not conduct. It is as if the diode were not there. The positive half cycle is unchanged at the output V(2) in Figure below. Since the output positive peaks actually overlays the input sinewave V(1), the input has been shifted upward in the plot for clarity. In Nutmeg, the SPICE display module, the command "plot v(1)+1)" accomplishes this.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="23024.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/23024.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">V(1)+1 is actually V(1), a 5 Vptp sinewave, offset by 1 V for display clarity. V(2) output is clipped at -0.7 V, by diode D1.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">During the negative half cycle of sinewave input of Figure above, the diode is forward biased, that is, conducting. The negative half cycle of the sinewave is shorted out. The negative half cycle of V(2) would be clipped at 0 V for an ideal diode. The waveform is clipped at -0.7 V due to the forward voltage drop of the silicon diode. The spice model defaults to 0.7 V unless parameters in the model statement specify otherwise. Germanium or Schottky diodes clip at lower voltages.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Closer examination of the negative clipped peak (Figure above) reveals that it follows the input for a slight period of time while the sinewave is moving toward -0.7 V. The clipping action is only effective after the input sinewave exceeds -0.7 V. The diode is not conducting for the complete half cycle, though, during most of it.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The addition of an anti-parallel diode to the existing diode in Figure above yields the symmetrical clipper in Figure below.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03438.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<table border="1" style="background-color: lightcyan; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><tbody style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03438.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><pre style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">*SPICE 03438.eps D1 0 2 diode D2 2 0 diode R1 2 1 1.0k V1 1 0 SIN(0 5 1k) .model diode d .tran 0.05m 3m .end </span></pre></td></tr>
</tbody></table><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Symmetrical clipper: Anti-parallel diodes clip both positive and negative peak, leaving a ± 0.7 V output.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diode D1 clips the negative peak at -0.7 V as before. The additional diode D2 conducts for positive half cycles of the sine wave as it exceeds 0.7 V, the forward diode drop. The remainder of the voltage drops across the series resistor. Thus, both peaks of the input sinewave are clipped in Figure below. The net list is in Figure above</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="23025.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/23025.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diode D1 clips at -0.7 V as it conducts during negative peaks. D2 conducts for positive peaks, clipping at 0.7V.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The most general form of the diode clipper is shown in Figure below. For an ideal diode, the clipping occurs at the level of the clipping voltage, V1 and V2. However, the voltage sources have been adjusted to account for the 0.7 V forward drop of the real silicon diodes. D1 clips at 1.3V +0.7V=2.0V when the diode begins to conduct. D2 clips at -2.3V -0.7V=-3.0V when D2 conducts.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03439.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<table border="1" style="background-color: lightcyan; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><tbody style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03439.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><pre style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">*SPICE 03439.eps V1 3 0 1.3 V2 4 0 -2.3 D1 2 3 diode D2 4 2 diode R1 2 1 1.0k V3 1 0 SIN(0 5 1k) .model diode d .tran 0.05m 3m .end </span></pre></td></tr>
</tbody></table><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">D1 clips the input sinewave at 2V. D2 clips at -3V.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The clipper in Figure above does not have to clip both levels. To clip at one level with one diode and one voltage source, remove the other diode and source.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The net list is in Figure above. The waveforms in Figure below show the clipping of v(1) at output v(2).</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="23026.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/23026.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">D1 clips the sinewave at 2V. D2 clips at -3V.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">There is also a zener diode clipper circuit in the "Zener diode" section. A zener diode replaces both the diode and the DC voltage source.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A practical application of a clipper is to prevent an amplified speech signal from overdriving a radio transmitter in Figure below. Over driving the transmitter generates spurious radio signals which causes interference with other stations. The clipper is a protective measure.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03440.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03440.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Clipper prevents over driving radio transmitter by voice peaks.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A sinewave may be squared up by overdriving a clipper. Another clipper application is the protection of exposed inputs of integrated circuits. The input of the IC is connected to a pair of diodes as at node "2" of Figure above . The voltage sources are replaced by the power supply rails of the IC. For example, CMOS IC's use 0V and +5 V. Analog amplifiers might use ±12V for the V1 and V2 sources.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></div><h1 style="font-size: 27px; font-weight: normal; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0.6em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Clamper circuits</span></h1><div><div style="background-color: #ffce7b; border-bottom-color: rgb(255, 165, 0); border-bottom-style: solid; border-bottom-width: 1px; border-left-color: rgb(255, 165, 0); border-left-style: solid; border-left-width: 1px; border-right-color: rgb(255, 165, 0); border-right-style: solid; border-right-width: 1px; border-top-color: rgb(255, 165, 0); border-top-style: solid; border-top-width: 1px; font-weight: bold; margin-bottom: 1em; margin-left: 0px; margin-right: 0px; margin-top: 2em; padding-bottom: 0.5em; padding-left: 1em; padding-right: 1em; padding-top: 0.5em; text-align: center; vertical-align: middle;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Clamper circuit" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Restorer circuit" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="DC restorer circuit" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The circuits in Figure below are known as </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">clampers</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> or </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">DC restorers</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">. The corresponding netlist is in Figure below. These circuits clamp a peak of a waveform to a specific DC level compared with a capacitively coupled signal which swings about its average DC level (usually 0V). If the diode is removed from the clamper, it defaults to a simple coupling capacitor– no clamping.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">What is the clamp voltage? And, which peak gets clamped? In Figure below (a) the clamp voltage is 0 V ignoring diode drop, (more exactly 0.7 V with Si diode drop). In Figure below, the positive peak of V(1) is clamped to the 0 V (0.7 V) clamp level. Why is this? On the first positive half cycle, the diode conducts charging the capacitor left end to +5 V (4.3 V). This is -5 V (-4.3 V) on the right end at V(1,4). Note the polarity marked on the capacitor in Figure below (a). The right end of the capacitor is -5 V DC (-4.3 V) with respect to ground. It also has an AC 5 V peak sinewave coupled across it from source V(4) to node 1. The sum of the two is a 5 V peak sine riding on a - 5 V DC (-4.3 V) level. The diode only conducts on successive positive excursions of source V(4) if the peak V(4) exceeds the charge on the capacitor. This only happens if the charge on the capacitor drained off due to a load, not shown. The charge on the capacitor is equal to the positive peak of V(4) (less 0.7 diode drop). The AC riding on the negative end, right end, is shifted down. The positive peak of the waveform is clamped to 0 V (0.7 V) because the diode conducts on the positive peak.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03443.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="58" src="http://sub.allaboutcircuits.com/images/03443.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Clampers: (a) Positive peak clamped to 0 V. (b) Negative peak clamped to 0 V. (c) Negative peak clamped to 5 V.</span></i></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="23028.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<table border="1" style="background-color: lightcyan; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><tbody style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/23028.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><pre style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">*SPICE 03443.eps V1 6 0 5 D1 6 3 diode C1 4 3 1000p D2 0 2 diode C2 4 2 1000p C3 4 1 1000p D3 1 0 diode V2 4 0 SIN(0 5 1k) .model diode d .tran 0.01m 5m .end </span></pre></td></tr>
</tbody></table><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">V(4) source voltage 5 V peak used in all clampers. V(1) clamper output from Figure above (a). V(1,4) DC voltage on capacitor in Figure (a). V(2) clamper output from Figure (b). V(3) clamper output from Figure (c).</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Suppose the polarity of the diode is reversed as in Figure above (b)? The diode conducts on the negative peak of source V(4). The negative peak is clamped to 0 V (-0.7 V). See V(2) in Figure above.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The most general realization of the clamper is shown in Figure above (c) with the diode connected to a DC reference. The capacitor still charges during the negative peak of the source. Note that the polarities of the AC source and the DC reference are series aiding. Thus, the capacitor charges to the sum to the two, 10 V DC (9.3 V). Coupling the 5 V peak sinewave across the capacitor yields Figure above V(3), the sum of the charge on the capacitor and the sinewave. The negative peak appears to be clamped to 5 V DC (4.3V), the value of the DC clamp reference (less diode drop).</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Describe the waveform if the DC clamp reference is changed from 5 V to 10 V. The clamped waveform will shift up. The negative peak will be clamped to 10 V (9.3). Suppose that the amplitude of the sine wave source is increased from 5 V to 7 V? The negative peak clamp level will remain unchanged. Though, the amplitude of the sinewave output will increase.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">An application of the clamper circuit is as a "DC restorer" in "composite video" circuitry in both television transmitters and receivers. An NTSC (US video standard) video signal "white level" corresponds to minimum (12.5%) transmitted power. The video "black level" corresponds to a high level (75% of transmitter power. There is a "blacker than black level" corresponding to 100% transmitted power assigned to synchronization signals. The NTSC signal contains both video and synchronization pulses. The problem with the composite video is that its average DC level varies with the scene, dark vs light. The video itself is supposed to vary. However, the sync must always peak at 100%. To prevent the sync signals from drifting with changing scenes, a "DC restorer" clamps the top of the sync pulses to a voltage corresponding to 100% transmitter modulation.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><h1 style="font-size: 27px; font-weight: normal; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0.6em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Voltage multipliers</span></h1><div><div style="background-color: #ffce7b; border-bottom-color: rgb(255, 165, 0); border-bottom-style: solid; border-bottom-width: 1px; border-left-color: rgb(255, 165, 0); border-left-style: solid; border-left-width: 1px; border-right-color: rgb(255, 165, 0); border-right-style: solid; border-right-width: 1px; border-top-color: rgb(255, 165, 0); border-top-style: solid; border-top-width: 1px; font-weight: bold; margin-bottom: 1em; margin-left: 0px; margin-right: 0px; margin-top: 2em; padding-bottom: 0.5em; padding-left: 1em; padding-right: 1em; padding-top: 0.5em; text-align: center; vertical-align: middle;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Voltage multiplier circuit" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Multiplier circuit, diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Voltage doubler circuit" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">voltage multiplier</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> is a specialized rectifier circuit producing an output which is theoretically an integer times the AC peak input, for example, 2, 3, or 4 times the AC peak input. Thus, it is possible to get 200 VDC from a 100 V</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">peak</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;"> AC source using a doubler, 400 VDC from a quadrupler. Any load in a practical circuit will lower these voltages.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A voltage doubler application is a DC power supply capable of using either a 240 VAC or 120 VAC source. The supply uses a switch selected full-wave bridge to produce about 300 VDC from a 240 VAC source. The 120 V position of the switch rewires the bridge as a doubler producing about 300 VDC from the 120 VAC. In both cases, 300 VDC is produced. This is the input to a switching regulator producing lower voltages for powering, say, a personal computer.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The half-wave voltage doubler in Figure below (a) is composed of two circuits: a clamper at (b) and peak detector (half-wave rectifier) in Figure prior, which is shown in modified form in Figure below (c). C2 has been added to a peak detector (half-wave rectifier).</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03255.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="50" src="http://sub.allaboutcircuits.com/images/03255.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Half-wave voltage doubler (a) is composed of (b) a clamper and (c) a half-wave rectifier.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Referring to Figure above (b), C2 charges to 5 V (4.3 V considering the diode drop) on the negative half cycle of AC input. The right end is grounded by the conducting D2. The left end is charged at the negative peak of the AC input. This is the operation of the clamper.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">During the positive half cycle, the half-wave rectifier comes into play at Figure above (c). Diode D2 is out of the circuit since it is reverse biased. C2 is now in series with the voltage source. Note the polarities of the generator and C2, series aiding. Thus, rectifier D1 sees a total of 10 V at the peak of the sinewave, 5 V from generator and 5 V from C2. D1 conducts waveform v(1) (Figure below), charging C1 to the peak of the sine wave riding on 5 V DC (Figure below v(2)). Waveform v(2) is the output of the doubler, which stabilizes at 10 V (8.6 V with diode drops) after a few cycles of sinewave input.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="23029.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<table border="1" style="background-color: lightcyan; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><tbody style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/23029.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><pre style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">*SPICE 03255.eps C1 2 0 1000p D1 1 2 diode C2 4 1 1000p D2 0 1 diode V1 4 0 SIN(0 5 1k) .model diode d .tran 0.01m 5m .end </span></pre></td></tr>
</tbody></table><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Voltage doubler: v(4) input. v(1) clamper stage. v(2) half-wave rectifier stage, which is the doubler output.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">full-wave voltage doubler</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> is composed of a pair of series stacked half-wave rectifiers. (Figure below) The corresponding netlist is in Figure below. The bottom rectifier charges C1 on the negative half cycle of input. The top rectifier charges C2 on the positive halfcycle. Each capacitor takes on a charge of 5 V (4.3 V considering diode drop). The output at node 5 is the series total of C1 + C2 or 10 V (8.6 V with diode drops).</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03273.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<table border="1" style="background-color: lightcyan; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><tbody style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03273.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><pre style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">*SPICE 03273.eps *R1 3 0 100k *R2 5 3 100k D1 0 2 diode D2 2 5 diode C1 3 0 1000p C2 5 3 1000p V1 2 3 SIN(0 5 1k) .model diode d .tran 0.01m 5m .end </span></pre></td></tr>
</tbody></table><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Full-wave voltage doubler consists of two half-wave rectifiers operating on alternating polarities.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Note that the output v(5) Figure below reaches full value within one cycle of the input v(2) excursion.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="23030.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/23030.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Full-wave voltage doubler: v(2) input, v(3)voltage at mid point, v(5) voltage at output</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Figure below illustrates the derivation of the full-wave doubler from a pair of opposite polarity half-wave rectifiers (a). The negative rectifier of the pair is redrawn for clarity (b). Both are combined at (c) sharing the same ground. At (d) the negative rectifier is re-wired to share one voltage source with the positive rectifier. This yields a ±5 V (4.3 V with diode drop) power supply; though, 10 V is measurable between the two outputs. The ground reference point is moved so that +10 V is available with respect to ground.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03274.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="81" src="http://sub.allaboutcircuits.com/images/03274.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Full-wave doubler: (a) Pair of doublers, (b) redrawn, (c) sharing the ground, (d) share the same voltage source. (e) move the ground point.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">voltage tripler</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> (Figure below) is built from a combination of a doubler and a half wave rectifier (C3, D3). The half-wave rectifier produces 5 V (4.3 V) at node 3. The doubler provides another 10 V (8.4 V) between nodes 2 and 3. for a total of 15 V (12.9 V) at the output node 2 with respect to ground. The netlist is in Figure below.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03283.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03283.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Voltage tripler composed of doubler stacked atop a single stage rectifier.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Note that V(3) in Figure below rises to 5 V (4.3 V) on the first negative half cycle. Input v(4) is shifted upward by 5 V (4.3 V) due to 5 V from the half-wave rectifier. And 5 V more at v(1) due to the clamper (C2, D2). D1 charges C1 (waveform v(2)) to the peak value of v(1).</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="23031.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<table border="1" style="background-color: lightcyan; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><tbody style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/23031.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><pre style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">*SPICE 03283.eps C3 3 0 1000p D3 0 4 diode C1 2 3 1000p D1 1 2 diode C2 4 1 1000p D2 3 1 diode V1 4 3 SIN(0 5 1k) .model diode d .tran 0.01m 5m .end </span></pre></td></tr>
</tbody></table><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Voltage tripler: v(3) half-wave rectifier, v(4) input+ 5 V, v(1) clamper, v(2) final output.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">voltage quadrupler</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> is a stacked combination of two doublers shown in Figure below. Each doubler provides 10 V (8.6 V) for a series total at node 2 with respect to ground of 20 V (17.2 V). The netlist is in Figure below.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03286.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03286.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Voltage quadrupler, composed of two doublers stacked in series, with output at node 2.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The waveforms of the quadrupler are shown in Figure below. Two DC outputs are available: v(3), the doubler output, and v(2) the quadrupler output. Some of the intermediate voltages at clampers illustrate that the input sinewave (not shown), which swings by 5 V, is successively clamped at higher levels: at v(5), v(4) and v(1). Strictly v(4) is not a clamper output. It is simply the AC voltage source in series with the v(3) the doubler output. None the less, v(1) is a clamped version of v(4)</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="23032.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<table border="1" style="background-color: lightcyan; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><tbody style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/23032.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><pre style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">*SPICE 03441.eps *SPICE 03286.eps C22 4 5 1000p C11 3 0 1000p D11 0 5 diode D22 5 3 diode C1 2 3 1000p D1 1 2 diode C2 4 1 1000p D2 3 1 diode V1 4 3 SIN(0 5 1k) .model diode d .tran 0.01m 5m .end </span></pre></td></tr>
</tbody></table><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Voltage quadrupler: DC voltage available at v(3) and v(2). Intermediate waveforms: Clampers: v(5), v(4), v(1).</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Some notes on voltage multipliers are in order at this point. The circuit parameters used in the examples (V= 5 V 1 kHz, C=1000 pf) do not provide much current, microamps. Furthermore, load resistors have been omitted. Loading reduces the voltages from those shown. If the circuits are to be driven by a kHz source at low voltage, as in the examples, the capacitors are usually 0.1 to 1.0 µF so that milliamps of current are available at the output. If the multipliers are driven from 50/60 Hz, the capacitor are a few hundred to a few thousand microfarads to provide hundreds of milliamps of output current. If driven from line voltage, pay attention to the polarity and voltage ratings of the capacitors.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Finally, any direct line driven power supply (no transformer) is dangerous to the experimenter and line operated test equipment. Commercial direct driven supplies are safe because the hazardous circuitry is in an enclosure to protect the user. When breadboarding these circuits with electrolytic capacitors of any voltage, the capacitors will explode if the polarity is reversed. Such circuits should be powered up behind a safety shield.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Cockcroft-Walton, voltage multiplier" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Voltage multiplier, Cockcroft-Walton" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A voltage multiplier of cascaded half-wave doublers of arbitrary length is known as a </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Cockcroft-Walton </span></i><span class="Apple-style-span" style="font-family: georgia, serif;">multiplier as shown in Figure below. This multiplier is used when a high voltage at low current is required. The advantage over a conventional supply is that an expensive high voltage transformer is not required– at least not as high as the output.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03288.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="48" src="http://sub.allaboutcircuits.com/images/03288.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Cockcroft-Walton x8 voltage multiplier; output at v(8).</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The pair of diodes and capacitors to the left of nodes 1 and 2 in Figure above constitute a half-wave doubler. Rotating the diodes by 45</span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">o</span></sup><span class="Apple-style-span" style="font-family: georgia, serif;">counterclockwise, and the bottom capacitor by 90</span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">o</span></sup><span class="Apple-style-span" style="font-family: georgia, serif;"> makes it look like Figure prior (a). Four of the doubler sections are cascaded to the right for a theoretical x8 multiplication factor. Node 1 has a clamper waveform (not shown), a sinewave shifted up by 1x (5 V). The other odd numbered nodes are sinewaves clamped to successively higher voltages. Node 2, the output of the first doubler, is a 2x DC voltage v(2) in Figure below. Successive even numbered nodes charge to successively higher voltages: v(4), v(6), v(8)</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="23033.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<table border="1" style="background-color: lightcyan; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><tbody style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/23033.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><pre style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">D1 7 8 diode C1 8 6 1000p D2 6 7 diode C2 5 7 1000p D3 5 6 diode C3 4 6 1000p D4 4 5 diode C4 3 5 1000p D5 3 4 diode C5 2 4 1000p D6 2 3 diode D7 1 2 diode C6 1 3 1000p C7 2 0 1000p C8 99 1 1000p D8 0 1 diode V1 99 0 SIN(0 5 1k) .model diode d .tran 0.01m 50m .end </span></pre></td></tr>
</tbody></table><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Cockcroft-Walton (x8) waveforms. Output is v(8).</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Without diode drops, each doubler yields 2Vin or 10 V, considering two diode drops (10-1.4)=8.6 V is realistic. For a total of 4 doublers one expects 4·8.6=34.4 V out of 40 V. Consulting Figure above, v(2) is about right;however, v(8) is <30 V instead of the anticipated 34.4 V. The bane of the Cockcroft-Walton multiplier is that each additional stage adds less than the previous stage. Thus, a practical limit to the number of stages exist. It is possible to overcome this limitation with a modification to the basic circuit. [ABR] Also note the time scale of 40 msec compared with 5 ms for previous circuits. It required 40 msec for the voltages to rise to a terminal value for this circuit. The netlist in Figure above has a ".tran 0.010m 50m" command to extend the simulation time to 50 msec; though, only 40 msec is plotted.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The Cockcroft-Walton multiplier serves as a more efficient high voltage source for photomultiplier tubes requiring up to 2000 V. [ABR] Moreover, the tube has numerous </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">dynodes</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">, terminals requiring connection to the lower voltage "even numbered" nodes. The series string of multiplier taps replaces a heat generating resistive voltage divider of previous designs.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">An AC line operated Cockcroft-Walton multiplier provides high voltage to "ion generators" for neutralizing electrostatic charge and for air purifiers.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></div><h1 style="font-size: 27px; font-weight: normal; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0.6em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Inductor commutating circuits</span></h1><div><div style="background-color: #ffce7b; border-bottom-color: rgb(255, 165, 0); border-bottom-style: solid; border-bottom-width: 1px; border-left-color: rgb(255, 165, 0); border-left-style: solid; border-left-width: 1px; border-right-color: rgb(255, 165, 0); border-right-style: solid; border-right-width: 1px; border-top-color: rgb(255, 165, 0); border-top-style: solid; border-top-width: 1px; font-weight: bold; margin-bottom: 1em; margin-left: 0px; margin-right: 0px; margin-top: 2em; padding-bottom: 0.5em; padding-left: 1em; padding-right: 1em; padding-top: 0.5em; text-align: center; vertical-align: middle;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Kickback, inductive" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A popular use of diodes is for the mitigation of inductive "kickback:" the pulses of high voltage produced when direct current through an inductor is interrupted. Take, for example, this simple circuit in Figure below with no protection against inductive kickback.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03271.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="40" src="http://sub.allaboutcircuits.com/images/03271.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Inductive kickback: (a) Switch open. (b) Switch closed, electron current flows from battery through coil which has polarity matching battery. Magnetic field stores energy. (c) Switch open, Current still flows in coil due to collapsing magnetic field. Note polarity change on coil. (d) Coil voltage vs time.</span></i></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Faraday's Law" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">When the pushbutton switch is actuated, current goes through the inductor, producing a magnetic field around it. When the switch is de-actuated, its contacts open, interrupting current through the inductor, and causing the magnetic field to rapidly collapse. Because the voltage induced in a coil of wire is directly proportional to the </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">rate of change</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> over time of magnetic flux (Faraday's Law: e = NdΦ/dt), this rapid collapse of magnetism around the coil produces a high voltage "spike".</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Commutating diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">If the inductor in question is an electromagnet coil, such as in a solenoid or relay (constructed for the purpose of creating a physical force via its magnetic field when energized), the effect of inductive "kickback" serves no useful purpose at all. In fact, it is quite detrimental to the switch, as it causes excessive arcing at the contacts, greatly reducing their service life. Of the practical methods for mitigating the high voltage transient created when the switch is opened, none so simple as the so-called </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">commutating diode</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> in Figure below.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03272.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="51" src="http://sub.allaboutcircuits.com/images/03272.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Inductive kickback with protection: (a) Switch open. (b)Switch closed, storing energy in magnetic field. (c) Switch open, inductive kickback is shorted by diode.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">In this circuit, the diode is placed in parallel with the coil, such that it will be reverse-biased when DC voltage is applied to the coil through the switch. Thus, when the coil is energized, the diode conducts no current in Figure above (b).</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">However, when the switch is opened, the coil's inductance responds to the decrease in current by inducing a voltage of reverse polarity, in an effort to maintain current at the same magnitude and in the same direction. This sudden reversal of voltage polarity across the coil forward-biases the diode, and the diode provides a current path for the inductor's current, so that its stored energy is dissipated slowly rather than suddenly in Figure above (c).</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">As a result, the voltage induced in the coil by its collapsing magnetic field is quite low: merely the forward voltage drop of the diode, rather than hundreds of volts as before. Thus, the switch contacts experience a voltage drop equal to the battery voltage plus about 0.7 volts (if the diode is silicon) during this discharge time.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Commutating diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Commutation" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Snubber" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">In electronics parlance, </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">commutation</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> refers to the reversal of voltage polarity or current direction. Thus, the purpose of a </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">commutating diode</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> is to act whenever voltage reverses polarity, for example, on an inductor coil when current through it is interrupted. A less formal term for a commutating diode is </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">snubber</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">, because it "snubs" or "squelches" the inductive kickback.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Faraday's Law" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A noteworthy disadvantage of this method is the extra time it imparts to the coil's discharge. Because the induced voltage is clamped to a very low value, its rate of magnetic flux change over time is comparatively slow. Remember that Faraday's Law describes the magnetic flux rate-of-change (dΦ/dt) as being proportional to the induced, instantaneous voltage (</span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">e</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> or </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">v</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">). If the instantaneous voltage is limited to some low figure, then the rate of change of magnetic flux over time will likewise be limited to a low (slow) figure.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">If an electromagnet coil is "snubbed" with a commutating diode, the magnetic field will dissipate at a relatively slow rate compared to the original scenario (no diode) where the field disappeared almost instantly upon switch release. The amount of time in question will most likely be less than one second, but it will be measurably slower than without a commutating diode in place. This may be an intolerable consequence if the coil is used to actuate an electromechanical relay, because the relay will possess a natural "time delay" upon coil de-energization, and an unwanted delay of even a fraction of a second may wreak havoc in some circuits.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Unfortunately, one cannot eliminate the high-voltage transient of inductive kickback </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">and</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> maintain fast de-magnetization of the coil: Faraday's Law will not be violated. However, if slow de-magnetization is unacceptable, a compromise may be struck between transient voltage and time by allowing the coil's voltage to rise to some higher level (but not so high as without a commutating diode in place). The schematic in Figure below shows how this can be done.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03275.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="62" src="http://sub.allaboutcircuits.com/images/03275.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">(a) Commutating diode with series resistor. (b) Voltage waveform. (c) Level with no diode. (d) Level with diode, no resistor. (e) Compromise level with diode and resistor.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A resistor placed in series with the commutating diode allows the coil's induced voltage to rise to a level greater than the diode's forward voltage drop, thus hastening the process of de-magnetization. This, of course, will place the switch contacts under greater stress, and so the resistor must be sized to limit that transient voltage at an acceptable maximum level.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></div><h1 style="font-size: 27px; font-weight: normal; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0.6em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diode switching circuits</span></h1><div><div style="background-color: #ffce7b; border-bottom-color: rgb(255, 165, 0); border-bottom-style: solid; border-bottom-width: 1px; border-left-color: rgb(255, 165, 0); border-left-style: solid; border-left-width: 1px; border-right-color: rgb(255, 165, 0); border-right-style: solid; border-right-width: 1px; border-top-color: rgb(255, 165, 0); border-top-style: solid; border-top-width: 1px; font-weight: bold; margin-bottom: 1em; margin-left: 0px; margin-right: 0px; margin-top: 2em; padding-bottom: 0.5em; padding-left: 1em; padding-right: 1em; padding-top: 0.5em; text-align: center; vertical-align: middle;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diodes can perform switching and digital logic operations. Forward and reverse bias switch a diode between the low and high impedance states, respectively. Thus, it serves as a switch.</span></div><h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Logic</span></u></h3><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diodes can perform digital logic functions: AND, and OR. Diode logic was used in early digital computers. It only finds limited application today. Sometimes it is convenient to fashion a single logic gate from a few diodes.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03461.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="77" src="http://sub.allaboutcircuits.com/images/03461.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diode AND gate</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">An AND gate is shown in Figure above. Logic gates have inputs and an output (Y) which is a function of the inputs. The inputs to the gate are high (logic 1), say 10 V, or low, 0 V (logic 0). In the figure, the logic levels are generated by switches. If a switch is up, the input is effectively high (1). If the switch is down, it connects a diode cathode to ground, which is low (0). The output depends on the combination of inputs at A and B. The inputs and output are customarily recorded in a "truth table" at (c) to describe the logic of a gate. At (a) all inputs are high (1). This is recorded in the last line of the truth table at (c). The output, Y, is high (1) due to the V</span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">+</span></sup><span class="Apple-style-span" style="font-family: georgia, serif;"> on the top of the resistor. It is unaffected by open switches. At (b) switch A pulls the cathode of the connected diode low, pulling output Y low (0.7 V). This is recorded in the third line of the truth table. The second line of the truth table describes the output with the switches reversed from (b). Switch B pulls the diode and output low. The first line of the truth table recordes the Output=0 for both input low (0). The truth table describes a logical AND function. Summary: both inputs A and B high yields a high (1) out.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A two input OR gate composed of a pair of diodes is shown in Figure below. If both inputs are logic low at (a) as simulated by both switches "downward," the output Y is pulled low by the resistor. This logic zero is recorded in the first line of the truth table at (c). If one of the inputs is high as at (b), or the other input is high, or both inputs high, the diode(s) conduct(s), pulling the output Y high. These results are reordered in the second through fourth lines of the truth table. Summary: any input "high" is a high out at Y.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03462.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="71" src="http://sub.allaboutcircuits.com/images/03462.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">OR gate: (a) First line, truth table (TT). (b) Third line TT. (d) Logical OR of power line supply and back-up battery.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A backup battery may be OR-wired with a line operated DC power supply in Figure above (d) to power a load, even during a power failure. With AC power present, the line supply powers the load, assuming that it is a higher voltage than the battery. In the event of a power failure, the line supply voltage drops to 0 V; the battery powers the load. The diodes must be in series with the power sources to prevent a failed line supply from draining the battery, and to prevent it from over charging the battery when line power is available. Does your PC computer retain its BIOS setting when powered off? Does your VCR (video cassette recorder) retain the clock setting after a power failure? (PC Yes, old VCR no, new VCR yes.)</span></div><h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Analog switch</span></u></h3><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diodes can switch analog signals. A reverse biased diode appears to be an open circuit. A forward biased diode is a low resistance conductor. The only problem is isolating the AC signal being switched from the DC control signal. The circuit in Figure below is a parallel resonant network: resonant tuning inductor paralleled by one (or more) of the switched resonator capacitors. This parallel LC resonant circuit could be a preselector filter for a radio receiver. It could be the frequency determining network of an oscillator (not shown). The digital control lines may be driven by a microprocessor interface.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03463.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="77" src="http://sub.allaboutcircuits.com/images/03463.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diode switch: A digital control signal (low) selects a resonator capacitor by forward biasing the switching diode.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The large value DC blocking capacitor grounds the resonant tuning inductor for AC while blocking DC. It would have a low reactance compared to the parallel LC reactances. This prevents the anode DC voltage from being shorted to ground by the resonant tuning inductor. A switched resonator capacitor is selected by pulling the corresponding digital control low. This forward biases the switching diode. The DC current path is from +5 V through an RF choke (RFC), a switching diode, and an RFC to ground via the digital control. The purpose of the RFC at the +5 V is to keep AC out of the +5 V supply. The RFC in series with the digital control is to keep AC out of the external control line. The decoupling capacitor shorts the little AC leaking through the RFC to ground, bypassing the external digital control line.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">With all three digital control lines high (≥+5 V), no switched resonator capacitors are selected due to diode reverse bias. Pulling one or more lines low, selects one or more switched resonator capacitors, respectively. As more capacitors are switched in parallel with the resonant tuning inductor, the resonant frequency decreases.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The reverse biased diode capacitance may be substantial compared with very high frequency or ultra high frequency circuits. PIN diodes may be used as switches for lower capacitance.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></div><h1 style="font-size: 27px; font-weight: normal; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0.6em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Zener diodes</span></h1><div><div style="background-color: #ffce7b; border-bottom-color: rgb(255, 165, 0); border-bottom-style: solid; border-bottom-width: 1px; border-left-color: rgb(255, 165, 0); border-left-style: solid; border-left-width: 1px; border-right-color: rgb(255, 165, 0); border-right-style: solid; border-right-width: 1px; border-top-color: rgb(255, 165, 0); border-top-style: solid; border-top-width: 1px; font-weight: bold; margin-bottom: 1em; margin-left: 0px; margin-right: 0px; margin-top: 2em; padding-bottom: 0.5em; padding-left: 1em; padding-right: 1em; padding-top: 0.5em; text-align: center; vertical-align: middle;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">If we connect a diode and resistor in series with a DC voltage source so that the diode is forward-biased, the voltage drop across the diode will remain fairly constant over a wide range of power supply voltages as in Figure below (a).</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">According to the "diode equation" here, the current through a forward-biased PN junction is proportional to </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">e</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> raised to the power of the forward voltage drop. Because this is an exponential function, current rises quite rapidly for modest increases in voltage drop. Another way of considering this is to say that voltage dropped across a forward-biased diode changes little for large variations in diode current. In the circuit shown in Figure below (a), diode current is limited by the voltage of the power supply, the series resistor, and the diode's voltage drop, which as we know doesn't vary much from 0.7 volts. If the power supply voltage were to be increased, the resistor's voltage drop would increase almost the same amount, and the diode's voltage drop just a little. Conversely, a decrease in power supply voltage would result in an almost equal decrease in resistor voltage drop, with just a little decrease in diode voltage drop. In a word, we could summarize this behavior by saying that the diode is</span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">regulating</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> the voltage drop at approximately 0.7 volts.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Voltage regulation is a useful diode property to exploit. Suppose we were building some kind of circuit which could not tolerate variations in power supply voltage, but needed to be powered by a chemical battery, whose voltage changes over its lifetime. We could form a circuit as shown and connect the circuit requiring steady voltage across the diode, where it would receive an unchanging 0.7 volts.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">This would certainly work, but most practical circuits of any kind require a power supply voltage in excess of 0.7 volts to properly function. One way we could increase our voltage regulation point would be to connect multiple diodes in series, so that their individual forward voltage drops of 0.7 volts each would add to create a larger total. For instance, if we had ten diodes in series, the regulated voltage would be ten times 0.7, or 7 volts in Figure below (b).</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03284.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="47" src="http://sub.allaboutcircuits.com/images/03284.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Forward biased Si reference: (a) single diode, 0.7V, (b) 10-diodes in series 7.0V.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">So long as the battery voltage never sagged below 7 volts, there would always be about 7 volts dropped across the ten-diode "stack."</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">If larger regulated voltages are required, we could either use more diodes in series (an inelegant option, in my opinion), or try a fundamentally different approach. We know that diode forward voltage is a fairly constant figure under a wide range of conditions, but so is </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">reverse breakdown voltage</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">, and breakdown voltage is typically much, much greater than forward voltage. If we reversed the polarity of the diode in our single-diode regulator circuit and increased the power supply voltage to the point where the diode "broke down" (could no longer withstand the reverse-bias voltage impressed across it), the diode would similarly regulate the voltage at that breakdown point, not allowing it to increase further as in Figure below (a).</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03285.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="58" src="http://sub.allaboutcircuits.com/images/03285.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">(a) Reverse biased Si small-signal diode breaks down at about 100V. (b) Symbol for Zener diode.</span></i></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Zener diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Diode, zener" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Unfortunately, when normal rectifying diodes "break down," they usually do so destructively. However, it is possible to build a special type of diode that can handle breakdown without failing completely. This type of diode is called a </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">zener diode</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">, and its symbol looks like Figure above (b).</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">When forward-biased, zener diodes behave much the same as standard rectifying diodes: they have a forward voltage drop which follows the "diode equation" and is about 0.7 volts. In reverse-bias mode, they do not conduct until the applied voltage reaches or exceeds the so-called</span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">zener voltage</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">, at which point the diode is able to conduct substantial current, and in doing so will try to limit the voltage dropped across it to that zener voltage point. So long as the power dissipated by this reverse current does not exceed the diode's thermal limits, the diode will not be harmed.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Zener diodes are manufactured with zener voltages ranging anywhere from a few volts to hundreds of volts. This zener voltage changes slightly with temperature, and like common carbon-composition resistor values, may be anywhere from 5 percent to 10 percent in error from the manufacturer's specifications. However, this stability and accuracy is generally good enough for the zener diode to be used as a voltage regulator device in common power supply circuit in Figure below.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03287.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03287.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Zener diode regulator circuit, Zener voltage = 12.6V).</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Please take note of the zener diode's orientation in the above circuit: the diode is </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">reverse-biased</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">, and intentionally so. If we had oriented the diode in the "normal" way, so as to be forward-biased, it would only drop 0.7 volts, just like a regular rectifying diode. If we want to exploit this diode's reverse breakdown properties, we must operate it in its reverse-bias mode. So long as the power supply voltage remains above the zener voltage (12.6 volts, in this example), the voltage dropped across the zener diode will remain at approximately 12.6 volts.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Zener diode failure mode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Failure mode, zener diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Joule's Law" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Like any semiconductor device, the zener diode is sensitive to temperature. Excessive temperature will destroy a zener diode, and because it both drops voltage and conducts current, it produces its own heat in accordance with Joule's Law (P=IE). Therefore, one must be careful to design the regulator circuit in such a way that the diode's power dissipation rating is not exceeded. Interestingly enough, when zener diodes fail due to excessive power dissipation, they usually fail </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">shorted</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> rather than open. A diode failed in this manner is readily detected: it drops almost zero voltage when biased either way, like a piece of wire.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Let's examine a zener diode regulating circuit mathematically, determining all voltages, currents, and power dissipations. Taking the same form of circuit shown earlier, we'll perform calculations assuming a zener voltage of 12.6 volts, a power supply voltage of 45 volts, and a series resistor value of 1000 Ω (we'll regard the zener voltage to be </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">exactly</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> 12.6 volts so as to avoid having to qualify all figures as "approximate" in Figurebelow (a)</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">If the zener diode's voltage is 12.6 volts and the power supply's voltage is 45 volts, there will be 32.4 volts dropped across the resistor (45 volts - 12.6 volts = 32.4 volts). 32.4 volts dropped across 1000 Ω gives 32.4 mA of current in the circuit. (Figure below (b))</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03289.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="60" src="http://sub.allaboutcircuits.com/images/03289.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">(a) Zener Voltage regulator with 1000 Ω resistor. (b) Calculation of voltage drops and current.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Power is calculated by multiplying current by voltage (P=IE), so we can calculate power dissipations for both the resistor and the zener diode quite easily:</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/13049.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">A zener diode with a power rating of 0.5 watt would be adequate, as would a resistor rated for 1.5 or 2 watts of dissipation.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">If excessive power dissipation is detrimental, then why not design the circuit for the least amount of dissipation possible? Why not just size the resistor for a very high value of resistance, thus severely limiting current and keeping power dissipation figures very low? Take this circuit, for example, with a 100 kΩ resistor instead of a 1 kΩ resistor. Note that both the power supply voltage and the diode's zener voltage in Figure below are identical to the last example:</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03290.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03290.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Zener regulator with 100 kΩ resistor.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">With only 1/100 of the current we had before (324 µA instead of 32.4 mA), both power dissipation figures should be 100 times smaller:</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/13050.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Seems ideal, doesn't it? Less power dissipation means lower operating temperatures for both the diode and the resistor, and also less wasted energy in the system, right? A higher resistance value </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">does</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> reduce power dissipation levels in the circuit, but it unfortunately introduces another problem. Remember that the purpose of a regulator circuit is to provide a stable voltage </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">for another circuit</span></i><span class="Apple-style-span" style="font-family: georgia, serif;">. In other words, we're eventually going to power something with 12.6 volts, and this something will have a current draw of its own. Consider our first regulator circuit, this time with a 500 Ω load connected in parallel with the zener diode in Figure below.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03291.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="68" src="http://sub.allaboutcircuits.com/images/03291.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Zener regulator with 1000 Ω series resistor and 500 Ω load.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">If 12.6 volts is maintained across a 500 Ω load, the load will draw 25.2 mA of current. In order for the 1 kΩ series "dropping" resistor to drop 32.4 volts (reducing the power supply's voltage of 45 volts down to 12.6 across the zener), it still must conduct 32.4 mA of current. This leaves 7.2 mA of current through the zener diode.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Now consider our "power-saving" regulator circuit with the 100 kΩ dropping resistor, delivering power to the same 500 Ω load. What it is supposed to do is maintain 12.6 volts across the load, just like the last circuit. However, as we will see, it </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">cannot</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> accomplish this task. (Figure below)</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03292.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="68" src="http://sub.allaboutcircuits.com/images/03292.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Zener non-regulator with 100 KΩ series resistor with 500 Ω load.></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">With the larger value of dropping resistor in place, there will only be about 224 mV of voltage across the 500 Ω load, far less than the expected value of 12.6 volts! Why is this? If we actually had 12.6 volts across the load, it would draw 25.2 mA of current, as before. This load current would have to go through the series dropping resistor as it did before, but with a new (much larger!) dropping resistor in place, the voltage dropped across that resistor with 25.2 mA of current going through it would be 2,520 volts! Since we obviously don't have that much voltage supplied by the battery, this cannot happen.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The situation is easier to comprehend if we temporarily remove the zener diode from the circuit and analyze the behavior of the two resistors alone in Figure below.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03293.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="67" src="http://sub.allaboutcircuits.com/images/03293.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Non-regulator with Zener removed.</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Both the 100 kΩ dropping resistor and the 500 Ω load resistance are in series with each other, giving a total circuit resistance of 100.5 kΩ. With a total voltage of 45 volts and a total resistance of 100.5 kΩ, Ohm's Law (I=E/R) tells us that the current will be 447.76 µA. Figuring voltage drops across both resistors (E=IR), we arrive at 44.776 volts and 224 mV, respectively. If we were to re-install the zener diode at this point, it would "see" 224 mV across it as well, being in parallel with the load resistance. This is far below the zener breakdown voltage of the diode and so it will not "break down" and conduct current. For that matter, at this low voltage the diode wouldn't conduct even if it were forward-biased! Thus, the diode ceases to regulate voltage. At least 12.6 volts must be dropped across to "activate" it.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The analytical technique of removing a zener diode from a circuit and seeing whether or not enough voltage is present to make it conduct is a sound one. Just because a zener diode happens to be connected in a circuit doesn't guarantee that the full zener voltage will always be dropped across it! Remember that zener diodes work by </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">limiting</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> voltage to some maximum level; they cannot </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">make up</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> for a lack of voltage.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">In summary, any zener diode regulating circuit will function so long as the load's resistance is equal to or greater than some minimum value. If the load resistance is too low, it will draw too much current, dropping too much voltage across the series dropping resistor, leaving insufficient voltage across the zener diode to make it conduct. When the zener diode stops conducting current, it can no longer regulate voltage, and the load voltage will fall below the regulation point.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Our regulator circuit with the 100 kΩ dropping resistor must be good for some value of load resistance, though. To find this acceptable load resistance value, we can use a table to calculate resistance in the two-resistor series circuit (no diode), inserting the known values of total voltage and dropping resistor resistance, and calculating for an expected load voltage of 12.6 volts:</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/13051.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">With 45 volts of total voltage and 12.6 volts across the load, we should have 32.4 volts across R</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">dropping</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">:</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/13052.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">With 32.4 volts across the dropping resistor, and 100 kΩ worth of resistance in it, the current through it will be 324 µA:</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/13053.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Being a series circuit, the current is equal through all components at any given time:</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/13054.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Calculating load resistance is now a simple matter of Ohm's Law (R = E/I), giving us 38.889 kΩ:</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/13055.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Thus, if the load resistance is exactly 38.889 kΩ, there will be 12.6 volts across it, diode or no diode. Any load resistance smaller than 38.889 kΩ will result in a load voltage less than 12.6 volts, diode or no diode. With the diode in place, the load voltage will be regulated to a maximum of 12.6 volts for any load resistance </span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">greater</span></i><span class="Apple-style-span" style="font-family: georgia, serif;"> than 38.889 kΩ.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">With the original value of 1 kΩ for the dropping resistor, our regulator circuit was able to adequately regulate voltage even for a load resistance as low as 500 Ω. What we see is a tradeoff between power dissipation and acceptable load resistance. The higher-value dropping resistor gave us less power dissipation, at the expense of raising the acceptable minimum load resistance value. If we wish to regulate voltage for low-value load resistances, the circuit must be prepared to handle higher power dissipation.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Zener diodes regulate voltage by acting as complementary loads, drawing more or less current as necessary to ensure a constant voltage drop across the load. This is analogous to regulating the speed of an automobile by braking rather than by varying the throttle position: not only is it wasteful, but the brakes must be built to handle all the engine's power when the driving conditions don't demand it. Despite this fundamental inefficiency of design, zener diode regulator circuits are widely employed due to their sheer simplicity. In high-power applications where the inefficiencies would be unacceptable, other voltage-regulating techniques are applied. But even then, small zener-based circuits are often used to provide a "reference" voltage to drive a more efficient amplifier circuit controlling the main power.</span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Zener diodes are manufactured in standard voltage ratings listed in Table below. The table "Common zener diode voltages" lists common voltages for 0.3W and 1.3W parts. The wattage corresponds to die and package size, and is the power that the diode may dissipate without damage.</span></div><a href="" name="czdv.tbl" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><br />
<a href="" name="czdv.tbl" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Common zener diode voltages</span></i></div></a><br />
<table border="1" style="background-color: lightcyan; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><tbody style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">0.5W</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">2.7V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">3.0V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">3.3V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">3.6V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">3.9V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">4.3V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">4.7V</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">5.1V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">5.6V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">6.2V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">6.8V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">7.5V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">8.2V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">9.1V</span></td> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">10V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">11V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">12V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">13V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">15V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">16V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">18V</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">20V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">24V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">27V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">30V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">1.3W</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">4.7V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">5.1V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">5.6V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">6.2V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">6.8V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">7.5V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">8.2V</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">9.1V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">10V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">11V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">12V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">13V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">15V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">16V</span></td> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">18V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">20V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">22V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">24V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">27V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">30V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">33V</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">36V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">39V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">43V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">47V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">51V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">56V</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">62V</span></td> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">68V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">75V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">100V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">200V</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td></tr>
</tbody></table><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="clipper, zener diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Zener diode, clipper" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="zenerclip" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Zener diode clipper:</span></b><span class="Apple-style-span" style="font-family: georgia, serif;"> A clipping circuit which clips the peaks of waveform a approximately the zener voltage of the diodes. The circuit of Figure below has two zeners connected series opposing to symmetrically clip a waveform at nearly the Zener voltage. The resistor limits current drawn by the zeners to a safe value.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03445.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<table border="1" style="background-color: lightcyan; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><tbody style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03445.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><pre style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">*SPICE 03445.eps D1 4 0 diode D2 4 2 diode R1 2 1 1.0k V1 1 0 SIN(0 20 1k) .model diode d bv=10 .tran 0.001m 2m .end </span></pre></td></tr>
</tbody></table><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Zener diode clipper:</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The zener breakdown voltage for the diodes is set at 10 V by the diode model parameter "bv=10" in the spice net list in Figure above. This causes the zeners to clip at about 10 V. The back-to-back diodes clip both peaks. For a positive half-cycle, the top zener is reverse biased, breaking down at the zener voltage of 10 V. The lower zener drops approximately 0.7 V since it is forward biased. Thus, a more accurate clipping level is 10+0.7=10.7V. Similar negative half-cycle clipping occurs a -10.7 V. (Figure below) shows the clipping level at a little over ±10 V.</span></div><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="23034.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/23034.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Zener diode clipper: v(1) input is clipped at waveform v(2).</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span style="font-style: normal; line-height: 18px;"></span></span></i></div><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></i><br />
<i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><h1 style="font-size: 27px; font-weight: normal; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0.6em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Special-purpose diodes</span></h1><div><span style="color: #333333; font-family: Verdana, Arial, Tahoma, sans-serif; font-style: normal; line-height: 18px;"></span><br />
<span style="color: #333333; font-family: Verdana, Arial, Tahoma, sans-serif; font-style: normal; line-height: 18px;"><div style="background-color: #ffce7b; border-bottom-color: rgb(255, 165, 0); border-bottom-style: solid; border-bottom-width: 1px; border-left-color: rgb(255, 165, 0); border-left-style: solid; border-left-width: 1px; border-right-color: rgb(255, 165, 0); border-right-style: solid; border-right-width: 1px; border-top-color: rgb(255, 165, 0); border-top-style: solid; border-top-width: 1px; font-weight: bold; margin-bottom: 1em; margin-left: 0px; margin-right: 0px; margin-top: 2em; padding-bottom: 0.5em; padding-left: 1em; padding-right: 1em; padding-top: 0.5em; text-align: center; vertical-align: middle;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span></div><h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Schottky diodes</span></span></u></h3><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Schottky diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Diode, schottky" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Diode, hot carrier" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="hot carrier diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Schottky diodes</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> are constructed of a </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">metal</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">-to-N junction rather than a P-N semiconductor junction. Also known as </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">hot-carrier</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> diodes, Schottky diodes are characterized by fast switching times (low reverse-recovery time), low forward voltage drop (typically 0.25 to 0.4 volts for a metal-silicon junction), and low junction capacitance.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The schematic symbol for a schottky diode is shown in Figure below.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03277.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03277.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Schottky diode schematic symbol.</span></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The forward voltage drop (V</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">F</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">), reverse-recovery time (t</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">rr</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">), and junction capacitance (C</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">J</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">) of Schottky diodes are closer to ideal than the average "rectifying" diode. This makes them well suited for high-frequency applications. Unfortunately, though, Schottky diodes typically have lower forward current (I</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">F</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">) and reverse voltage (V</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">RRM</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> and V</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">DC</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">) ratings than rectifying diodes and are thus unsuitable for applications involving substantial amounts of power. Though they are used in low voltage switching regulator power supplies.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Schottky diode technology finds broad application in high-speed computer circuits, where the fast switching time equates to high speed capability, and the low forward voltage drop equates to less power dissipation when conducting.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Switching regulator power supplies operating at 100's of kHz cannot use conventional silicon diodes as rectifiers because of their slow switching speed . When the signal applied to a diode changes from forward to reverse bias, conduction continues for a short time, while carriers are being swept out of the depletion region. Conduction only ceases after this t</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">r</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">reverse recovery time</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> has expired. Schottky diodes have a shorter reverse recovery time.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Regardless of switching speed, the 0.7 V forward voltage drop of silicon diodes causes poor efficiency in low voltage supplies. This is not a problem in, say, a 10 V supply. In a 1 V supply the 0.7 V drop is a substantial portion of the output. One solution is to use a schottky power diode which has a lower forward drop.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="esakiTD" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Tunnel diodes</span></span></u></h3><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Tunnel diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Diode, tunnel" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Tunnel diodes</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> exploit a strange quantum phenomenon called </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">resonant tunneling</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> to provide a negative resistance forward-bias characteristics. When a small forward-bias voltage is applied across a tunnel diode, it begins to conduct current. (Figure below(b)) As the voltage is increased, the current increases and reaches a peak value called the </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">peak current</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> (I</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">P</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">). If the voltage is increased a little more, the current actually begins to </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">decrease</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> until it reaches a low point called the </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">valley current</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> (I</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">V</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">). If the voltage is increased further yet, the current begins to increase again, this time without decreasing into another "valley." The schematic symbol for the tunnel diode shown in Figure below(a).</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03278.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="51" src="http://sub.allaboutcircuits.com/images/03278.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Tunnel diode (a) Schematic symbol. (b) Current vs voltage plot (c) Oscillator.</span></span></i></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Negative resistance" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Resistance, negative" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The forward voltages necessary to drive a tunnel diode to its peak and valley currents are known as peak voltage (V</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">P</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">) and valley voltage (V</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">V</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">), respectively. The region on the graph where current is decreasing while applied voltage is increasing (between V</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">P</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> and V</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">V</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> on the horizontal scale) is known as the region of </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">negative resistance</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Esaki diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Diode, Esaki" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Tunnel diodes, also known as </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Esaki diodes</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> in honor of their Japanese inventor Leo Esaki, are able to transition between peak and valley current levels very quickly, "switching" between high and low states of conduction much faster than even Schottky diodes. Tunnel diode characteristics are also relatively unaffected by changes in temperature.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03469.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03469.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Reverse breakdown voltage versus doping level. After Sze [SGG]</span></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Tunnel diodes are heavily doped in both the P and N regions, 1000 times the level in a rectifier. This can be seen in Figure above. Standard diodes are to the far left, zener diodes near to the left, and tunnel diodes to the right of the dashed line. The heavy doping produces an unusually thin depletion region. This produces an unusually low reverse breakdown voltage with high leakage. The thin depletion region causes high capacitance. To overcome this, the tunnel diode junction area must be tiny. The forward diode characteristic consists of two regions: a normal forward diode characteristic with current rising exponentially beyond V</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">F</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">, 0.3 V for Ge, 0.7 V for Si. Between 0 V and V</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">F</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> is an additional "negative resistance" characteristic peak. This is due to quantum mechanical tunneling involving the dual particle-wave nature of electrons. The depletion region is thin enough compared with the equivalent wavelength of the electron that they can tunnel through. They do not have to overcome the normal forward diode voltage V</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">F</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">. The energy level of the conduction band of the N-type material overlaps the level of the valence band in the P-type region. With increasing voltage, tunneling begins; the levels overlap; current increases, up to a point. As current increases further, the energy levels overlap less; current decreases with increasing voltage. This is the "negative resistance" portion of the curve.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Tunnel diodes are not good rectifiers, as they have relatively high "leakage" current when reverse-biased. Consequently, they find application only in special circuits where their unique tunnel effect has value. To exploit the tunnel effect, these diodes are maintained at a bias voltage somewhere between the peak and valley voltage levels, always in a forward-biased polarity (anode positive, and cathode negative).</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Perhaps the most common application of a tunnel diode is in simple high-frequency oscillator circuits as in Figure above(c), where it allows a DC voltage source to contribute power to an LC "tank" circuit, the diode conducting when the voltage across it reaches the peak (tunnel) level and effectively insulating at all other voltages. The resistors bias the tunnel diode at a few tenths of a volt centered on the negative resistance portion of the characteristic curve. The L-C resonant circuit may be a section of waveguide for microwave operation. Oscillation to 5 GHz is possible.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">At one time the tunnel diode was the only solid-state microwave amplifier available. Tunnel diodes were popular starting in the 1960's. They were longer lived than traveling wave tube amplifiers, an important consideration in satellite transmitters. Tunnel diodes are also resistant to radiation because of the heavy doping. Today various transistors operate at microwave frequencies. Even small signal tunnel diodes are expensive and difficult to find today. There is one remaining manufacturer of germanium tunnel diodes, and none for silicon devices. They are sometimes used in military equipment because they are insensitive to radiation and large temperature changes.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">There has been some research involving possible integration of silicon tunnel diodes into CMOS integrated circuits. They are thought to be capable of switching at 100 GHz in digital circuits. The sole manufacturer of germanium devices produces them one at a time. A batch process for silicon tunnel diodes must be developed, then integrated with conventional CMOS processes. [SZL]</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The Esaki tunnel diode should not be confused with the </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">resonant tunneling diode</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> CH 2, of more complex construction from compound semiconductors. The RTD is a more recent development capable of higher speed.</span></span></div><h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Light-emitting diodes</span></span></u></h3><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diodes, like all semiconductor devices, are governed by the principles described in quantum physics. One of these principles is the emission of specific-frequency radiant energy whenever electrons fall from a higher energy level to a lower energy level. This is the same principle at work in a neon lamp, the characteristic pink-orange glow of ionized neon due to the specific energy transitions of its electrons in the midst of an electric current. The unique color of a neon lamp's glow is due to the fact that its </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">neon</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> gas inside the tube, and not due to the particular amount of current through the tube or voltage between the two electrodes. Neon gas glows pinkish-orange over a wide range of ionizing voltages and currents. Each chemical element has its own "signature" emission of radiant energy when its electrons "jump" between different, quantized energy levels. Hydrogen gas, for example, glows red when ionized; mercury vapor glows blue. This is what makes spectrographic identification of elements possible.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Light-emitting diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Diode, light-emitting" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="LED" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Electrons flowing through a PN junction experience similar transitions in energy level, and emit radiant energy as they do so. The frequency of this radiant energy is determined by the crystal structure of the semiconductor material, and the elements comprising it. Some semiconductor junctions, composed of special chemical combinations, emit radiant energy within the spectrum of visible light as the electrons change energy levels. Simply put, these junctions </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">glow</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> when forward biased. A diode intentionally designed to glow like a lamp is called a </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">light-emitting diode</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">, or</span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">LED</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Forward biased silicon diodes give off heat as electron and holes from the N-type and P-type regions, respectively, recombine at the junction. In a forward biased LED, the recombination of electrons and holes in the active region in Figure below (c) yields photons. This process is known as</span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">electroluminescence</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">. To give off photons, the potential barrier through which the electrons fall must be higher than for a silicon diode. The forward diode drop can range to a few volts for some color LEDs.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diodes made from a combination of the elements gallium, arsenic, and phosphorus (called </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">gallium-arsenide-phosphide</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">) glow bright red, and are some of the most common LEDs manufactured. By altering the chemical constituency of the PN junction, different colors may be obtained. Early generations of LEDs were red, green, yellow, orange, and infra-red, later generations included blue and ultraviolet, with violet being the latest color added to the selection. Other colors may be obtained by combining two or more primary-color (red, green, and blue) LEDs together in the same package, sharing the same optical lens. This allowed for multicolor LEDs, such as tricolor LEDs (commercially available in the 1980's) using red and green (which can create yellow) and later RGB LEDs (red, green, and blue), which cover the entire color spectrum.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The schematic symbol for an LED is a regular diode shape inside of a circle, with two small arrows pointing away (indicating emitted light), shown in Figure below.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03294.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="61" src="http://sub.allaboutcircuits.com/images/03294.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">LED, Light Emitting Diode: (a) schematic symbol. (b) Flat side and short lead of device correspond to cathode. (c) Cross section of Led die.</span></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">This notation of having two small arrows pointing away from the device is common to the schematic symbols of all light-emitting semiconductor devices. Conversely, if a device is light-</span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">activated</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> (meaning that incoming light stimulates it), then the symbol will have two small arrows pointing</span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">toward</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> it. LEDs can sense light. They generate a small voltage when exposed to light, much like a solar cell on a small scale. This property can be gainfully applied in a variety of light-sensing circuits.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Because LEDs are made of different chemical substances than silicon diodes, their forward voltage drops will be different. Typically, LEDs have much larger forward voltage drops than rectifying diodes, anywhere from about 1.6 volts to over 3 volts, depending on the color. Typical operating current for a standard-sized LED is around 20 mA. When operating an LED from a DC voltage source greater than the LED's forward voltage, a series-connected "dropping" resistor must be included to prevent full source voltage from damaging the LED. Consider the example circuit in Figure below (a) using a 6 V source.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03295.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="49" src="http://sub.allaboutcircuits.com/images/03295.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Setting LED current at 20 ma. (a) for a 6 V source, (b) for a 24 V source.</span></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">With the LED dropping 1.6 volts, there will be 4.4 volts dropped across the resistor. Sizing the resistor for an LED current of 20 mA is as simple as taking its voltage drop (4.4 volts) and dividing by circuit current (20 mA), in accordance with Ohm's Law (R=E/I). This gives us a figure of 220 Ω. Calculating power dissipation for this resistor, we take its voltage drop and multiply by its current (P=IE), and end up with 88 mW, well within the rating of a 1/8 watt resistor. Higher battery voltages will require larger-value dropping resistors, and possibly higher-power rating resistors as well. Consider the example in Figure above (b) for a supply voltage of 24 volts:</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Here, the dropping resistor must be increased to a size of 1.12 kΩ to drop 22.4 volts at 20 mA so that the LED still receives only 1.6 volts. This also makes for a higher resistor power dissipation: 448 mW, nearly one-half a watt of power! Obviously, a resistor rated for 1/8 watt power dissipation or even 1/4 watt dissipation will overheat if used here.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Dropping resistor values need not be precise for LED circuits. Suppose we were to use a 1 kΩ resistor instead of a 1.12 kΩ resistor in the circuit shown above. The result would be a slightly greater circuit current and LED voltage drop, resulting in a brighter light from the LED and slightly reduced service life. A dropping resistor with too much resistance (say, 1.5 kΩ instead of 1.12 kΩ) will result in less circuit current, less LED voltage, and a dimmer light. LEDs are quite tolerant of variation in applied power, so you need not strive for perfection in sizing the dropping resistor.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Multiple LEDs are sometimes required, say in lighting. If LEDs are operated in parallel, each must have its own current limiting resistor as in Figure below (a) to ensure currents dividing more equally. However, it is more efficient to operate LEDs in series (Figure below (b)) with a single dropping resistor. As the number of series LEDs increases the series resistor value must decrease to maintain current, to a point. The number of LEDs in series (V</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">f</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">) cannot exceed the capability of the power supply. Multiple series strings may be employed as in Figure below (c).</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">In spite of equalizing the currents in multiple LEDs, the brightness of the devices may not match due to variations in the individual parts. Parts can be selected for brightness matching for critical applications.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03296.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="59" src="http://sub.allaboutcircuits.com/images/03296.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Multiple LEDs: (a) In parallel, (b) in series, (c) series-parallel</span></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Also because of their unique chemical makeup, LEDs have much, much lower peak-inverse voltage (PIV) ratings than ordinary rectifying diodes. A typical LED might only be rated at 5 volts in reverse-bias mode. Therefore, when using alternating current to power an LED, connect a protective rectifying diode anti-parallel with the LED to prevent reverse breakdown every other half-cycle as in Figure below (a).</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03298.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="44" src="http://sub.allaboutcircuits.com/images/03298.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Safely driving an LED with AC: (a) from 24 VAC, (b) from 240 VAC.</span></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">If the LED is driven from a 240 VAC source, the Figure above (a) voltage source is increased from 24 VAC to 240 VAC, the resistor from 1.12 kΩ to 12 kΩ. The power dissipated in the 12 kΩ resistor is an unattractive 4.8 watts.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /> </span></span><br />
<pre style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> P = VI = (240 V)(20 mA) = 4.8 watt </span></span></pre><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /> </span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">A potential solution is to replace the 12 kΩ resistor with a non-dissipative 12 kΩ capacitive reactance. This would be Figure above (b) with the resistor shorted. That circuit at (b), missing the resistor, was published in an electrical engineering journal. This author constructed the circuit. It worked the first time it was powered "on," but not thereafter upon "power on". Each time it was powered "on," it got dimmer until it failed completely. Why? If "power on" occurs near a zero crossing of the AC sinewave, the circuit works. However, if powered "on" at, say, the peak of the sinewave, the voltage rises abruptly from zero to the peak. Since the current through the capacitor is i = C(dv/dt), the current spikes to a very large value exceeding the "surge current" rating of the LED, destroying it.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The solution is to design a capacitor for the continuous current of the LED, and a series resistor to limit current during "power on" to the surge current rating of the LED. Often the surge current rating of an LED is ten times higher than the continuous current rating. (Though, this is not true of high current illumination grade LED's.) We calculate a capacitor to supply 20 mA continuous current, then select a resistor having resistance of 1/10 th the capacitive reactance.</span></span></div><pre style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> I = 20 mA X</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">c</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> = (240 V) / (20 mA) = 12 kΩ X</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">c</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> = 1/2πf</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">c</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> C = 1/2πX</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">c</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> = 1/2π60(12 kΩ = 0.22 µF R = (0.10)X</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">c</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">= (0.10)(12kΩ) = 1.2 kΩ P = I</span></span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">2</span></span></sup><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">R = (20 mA)</span></span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">2</span></span></sup><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">(1.2 kΩ) = 0.48 watt </span></span></pre><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The resistor limits the LED current to 200 mA during the "power on" surge. Thereafter it passes 20 mA as limited by the capacitor. The 1.2 kresistor dissipates 0.48 watts compared with 4.8 watts for the 12 kΩ resistor circuit.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">What component values would be required to operate the circuit on 120 VAC? One solution is to use the 240 VAC circuit on 120 VAC with no change in component values, halving the LED continuous current to 10 mA. If operation at 20 mA is required, double the capacitor value and halve the resistor value.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The anti-parallel diodes in Figure above can be replaced with an anti-parallel LED. The resulting pair of anti-parallel LED's illuminate on alternating half-cycles of the AC sinewave. This configuration draws 20 ma, splitting it equally between the LED's on alternating AC half cycles. Each LED only receives 10 mA due to this sharing. The same is true of the LED anti-parallel combination with a rectifier. The LED only receives 10 ma. If 20 mA was required for the LED(s), The capacitor value in µF could be doubled and the resistor halved.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The forward voltage drop of LED's is inversely proportional to the wavelength (λ). As wavelength decreases going from infrared to visible colors to ultraviolet, V</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">f</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> increases. While this trend is most obvious in the various devices from a single manufacturer, The voltage range for a particular color LED from various manufacturers varies. This range of voltages is shown in Table below.</span></span></div><a href="" name="leds.tbl" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><br />
<a href="" name="leds.tbl" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Optical and electrical properties of LED's</span></span></i></div></a><br />
<table border="1" style="background-color: lightcyan; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><tbody style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <th style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">LED</span></th> <th style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">λ nm (= 10 </span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">-9</span></sup><span class="Apple-style-span" style="font-family: georgia, serif;">m)</span></th> <th style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">V</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">f</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;">(from)</span></th> <th style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">V</span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">f</span></sub><span class="Apple-style-span" style="font-family: georgia, serif;"> (to)</span></th> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">infrared</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">940</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">1.2</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">1.7</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">red</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">660</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">1.5</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">2.4</span></td> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">orange</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">602-620</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">2.1</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">2.2</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">yellow, green</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">560-595</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">1.7</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">2.8</span></td> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">white, blue, violet</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">-</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">3</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">4</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">ultraviolet</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">370</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">4.2</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">4.8</span></td> </tr>
</tbody></table><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">As lamps, LEDs are superior to incandescent bulbs in many ways. First and foremost is efficiency: LEDs output far more light power per watt of electrical input than an incandescent lamp. This is a significant advantage if the circuit in question is battery-powered, efficiency translating to longer battery life. Second is the fact that LEDs are far more reliable, having a much greater service life than incandescent lamps. This is because LEDs are "cold" devices: they operate at much cooler temperatures than an incandescent lamp with a white-hot metal filament, susceptible to breakage from mechanical and thermal shock. Third is the high speed at which LEDs may be turned on and off. This advantage is also due to the "cold" operation of LEDs: they don't have to overcome thermal inertia in transitioning from off to on or vice versa. For this reason, LEDs are used to transmit digital (on/off) information as pulses of light, conducted in empty space or through fiber-optic cable, at very high rates of speed (millions of pulses per second).</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">LEDs excel in monochromatic lighting applications like traffic signals and automotive tail lights. Incandescents are abysmal in this application since they require filtering, decreasing efficiency. LEDs do not require filtering.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">One major disadvantage of using LEDs as sources of illumination is their monochromatic (single-color) emission. No one wants to read a book under the light of a red, green, or blue LED. However, if used in combination, LED colors may be mixed for a more broad-spectrum glow. A new broad spectrum light source is the white LED. While small white panel indicators have been available for many years, illumination grade devices are still in development.</span></span></div><a href="" name="lamps.tbl" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><br />
<a href="" name="lamps.tbl" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Efficiency of lighting</span></span></i></div></a><br />
<table border="1" style="background-color: lightcyan; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><tbody style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <th style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Lamp type</span></th> <th style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Efficiency lumen/watt</span></th> <th style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Life hrs</span></th> <th style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">notes</span></th> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">White LED</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">35</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">100,000</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">costly</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">White LED, future</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">100</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">100,000</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R&D target</span></td> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Incandescent</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">12</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">1000</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">inexpensive</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Halogen</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">15-17</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">2000</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">high quality light</span></td> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Compact fluorescent</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">50-100</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">10,000</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">cost effective</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Sodium vapor, lp</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">70-200</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">20,000</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">outdoor</span></td> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Mercury vapor</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">13-48</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">18,000</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">outdoor</span></td></tr>
</tbody></table><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">A white LED is a blue LED exciting a phosphor which emits yellow light. The blue plus yellow approximates white light. The nature of the phosphor determines the characteristics of the light. A red phosphor may be added to improve the quality of the yellow plus blue mixture at the expense of efficiency. Table above compares white illumination LEDs to expected future devices and other conventional lamps. Efficiency is measured in lumens of light output per watt of input power. If the 50 lumens/watt device can be improved to 100 lumens/watt, white LEDs will be comparable to compact fluorescent lamps in efficiency.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">LEDs in general have been a major subject of R&D since the 1960's. Because of this it is impractical to cover all geometries, chemistries, and characteristics that have been created over the decades. The early devices were relatively dim and took moderate currents. The efficiencies have been improved in later generations to the point it is hazardous to look closely and directly into an illuminated LED. This can result in eye damage, and the LEDs only required a minor increase in dropping voltage (Vf) and current. Modern high intensity devices have reached 180 lumens using 0.7 Amps (82 lumens/watt, Luxeon Rebel series cool white), and even higher intensity models can use even higher currents with a corresponding increase in brightness. Other developments, such as quantum dots, are the subject of current research, so expect to see new things for these devices in the future</span></span></div><h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Laser diodes</span></span></u></h3><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Laser diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Diode, laser" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">laser diode</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> is a further development upon the regular light-emitting diode, or LED. The term "laser" itself is actually an acronym, despite the fact its often written in lower-case letters. "Laser" stands for </span></span><b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">L</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">ight </span></span><b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">A</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">mplification by </span></span><b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">S</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">timulated </span></span><b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">E</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">mission of </span></span><b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">adiation, and refers to another strange quantum process whereby characteristic light emitted by electrons falling from high-level to low-level energy states in a material stimulate other electrons in a substance to make similar "jumps," the result being a synchronized output of light from the material. This synchronization extends to the actual </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">phase</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> of the emitted light, so that all light waves emitted from a "lasing" material are not just the same frequency (color), but also the same phase as each other, so that they reinforce one another and are able to travel in a very tightly-confined, nondispersing beam. This is why laser light stays so remarkably focused over long distances: each and every light wave coming from the laser is in step with each other.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03297.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="119" src="http://sub.allaboutcircuits.com/images/03297.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">(a) White light of many wavelengths. (b) Mono-chromatic LED light, a single wavelength. (c) Phase coherent laser light.</span></span></i></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Coherent light" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Monochromatic light" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Laser light" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Incandescent lamps produce "white" (mixed-frequency, or mixed-color) light as in Figure above (a). Regular LEDs produce monochromatic light: same frequency (color), but different phases, resulting in similar beam dispersion in Figure above (b). Laser LEDs produce </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">coherent light</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">: light that is both monochromatic (single-color) and monophasic (single-phase), resulting in precise beam confinement as in Figure above (c).</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Laser light finds wide application in the modern world: everything from surveying, where a straight and nondispersing light beam is very useful for precise sighting of measurement markers, to the reading and writing of optical disks, where only the narrowness of a focused laser beam is able to resolve the microscopic "pits" in the disk's surface comprising the binary 1's and 0's of digital information.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Some laser diodes require special high-power "pulsing" circuits to deliver large quantities of voltage and current in short bursts. Other laser diodes may be operated continuously at lower power. In the continuous laser, laser action occurs only within a certain range of diode current, necessitating some form of current-regulator circuit. As laser diodes age, their power requirements may change (more current required for less output power), but it should be remembered that low-power laser diodes, like LEDs, are fairly long-lived devices, with typical service lives in the tens of thousands of hours.</span></span></div><h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Photodiodes</span></span></u></h3><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Photodiode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Diode, light-activated" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">A </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">photodiode</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> is a diode optimized to produce an electron current flow in response to irradiation by ultraviolet, visible, or infrared light. Silicon is most often used to fabricate photodiodes; though, germanium and gallium arsenide can be used. The junction through which light enters the semiconductor must be thin enough to pass most of the light on to the active region (depletion region) where light is converted to electron hole pairs.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">In Figure below a shallow P-type diffusion into an N-type wafer produces a PN junction near the surface of the wafer. The P-type layer needs to be thin to pass as much light as possible. A heavy N+ diffusion on the back of the wafer makes contact with metalization. The top metalization may be a fine grid of metallic fingers on the top of the wafer for large cells. In small photodiodes, the top contact might be a sole bond wire contacting the bare P-type silicon top.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03446.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="100" src="http://sub.allaboutcircuits.com/images/03446.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Photodiode: Schematic symbol and cross section.</span></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Light entering the top of the photodiode stack fall off exponentially in with depth of the silicon. A thin top P-type layer allows most photons to pass into the depletion region where electron-hole pairs are formed. The electric field across the depletion region due to the built in diode potential causes electrons to be swept into the N-layer, holes into the P-layer. Actually electron-hole pairs may be formed in any of the semiconductor regions. However, those formed in the depletion region are most likely to be separated into the respective N and P-regions. Many of the electron-hole pairs formed in the P and N-regions recombine. Only a few do so in the depletion region. Thus, a few electron-hole pairs in the N and P-regions, and most in the depletion region contribute to </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">photocurrent</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">, that current resulting from light falling on the photodiode.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The voltage out of a photodiode may be observed. Operation in this </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">photovoltaic</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> (PV) mode is not linear over a large dynamic range, though it is sensitive and has low noise at frequencies less than 100 kHz. The preferred mode of operation is often </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">photocurrent (PC)</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> mode because the current is linearly proportional to light flux over several decades of intensity, and higher frequency response can be achieved. PC mode is achieved with reverse bias or zero bias on the photodiode. A current amplifier (transimpedance amplifier) should be used with a photodiode in PC mode. Linearity and PC mode are achieved as long as the diode does not become forward biased.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">High speed operation is often required of photodiodes, as opposed to solar cells. Speed is a function of diode capacitance, which can be minimized by decreasing cell area. Thus, a sensor for a high speed fiber optic link will use an area no larger than necessary, say 1 mm</span></span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">2</span></span></sup><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">. Capacitance may also be decreased by increasing the thickness of the depletion region, in the manufacturing process or by increasing the reverse bias on the diode.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Photodiode, PIN" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="PIN, photodiode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="PINphoto" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">PIN diode</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> The </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">p-i-n diode</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> or </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">PIN diode</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> is a photodiode with an intrinsic layer between the P and N-regions as in Figure below. The </span></span><b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">P</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">-</span></span><b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">I</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">ntrinsic-</span></span><b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">N</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">structure increases the distance between the P and N conductive layers, decreasing capacitance, increasing speed. The volume of the photo sensitive region also increases, enhancing conversion efficiency. The bandwidth can extend to 10's of gHz. PIN photodiodes are the preferred for high sensitivity, and high speed at moderate cost.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03447.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03447.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">PIN photodiode: The intrinsic region increases the thickness of the depletion region.</span></span></i></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Photodiode, APD" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Avalanche photodiode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Avalanche photo diode:</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">An </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">avalanche photodiode (APD)</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">designed to operate at high reverse bias exhibits an electron multiplier effect analogous to a photomultiplier tube. The reverse bias can run from 10's of volts to nearly 2000 V. The high level of reverse bias accelerates photon created electron-hole pairs in the intrinsic region to a high enough velocity to free additional carriers from collisions with the crystal lattice. Thus, many electrons per photon result. The motivation for the APD is to achieve amplification within the photodiode to overcome noise in external amplifiers. This works to some extent. However, the APD creates noise of its own. At high speed the APD is superior to a PIN diode amplifier combination, though not for low speed applications. APD's are expensive, roughly the price of a photomultiplier tube. So, they are only competitive with PIN photodiodes for niche applications. One such application is single photon counting as applied to nuclear physics.</span></span></div><h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Solar cells</span></span></u></h3><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Solar cell" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">A photodiode optimized for efficiently delivering power to a load is the </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">solar cell</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">. It operates in photovoltaic mode (PV) because it is forward biased by the voltage developed across the load resistance.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Monocrystalline solar cells are manufactured in a process similar to semiconductor processing. This involves growing a single crystal boule from molten high purity silicon (P-type), though, not as high purity as for semiconductors. The boule is diamond sawed or wire sawed into wafers. The ends of the boule must be discarded or recycled, and silicon is lost in the saw kerf. Since modern cells are nearly square, silicon is lost in squaring the boule. Cells may be etched to texture (roughen) the surface to help trap light within the cell. Considerable silicon is lost in producing the 10 or 15 cm square wafers. These days (2007) it is common for solar cell manufacturer to purchase the wafers at this stage from a supplier to the semiconductor industry.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">P-type Wafers are loaded back-to-back into fused silica boats exposing only the outer surface to the N-type dopant in the diffusion furnace. The diffusion process forms a thin n-type layer on the top of the cell. The diffusion also shorts the edges of the cell front to back. The periphery must be removed by plasma etching to unshort the cell. Silver and or aluminum paste is screened on the back of the cell, and a silver grid on the front. These are sintered in a furnace for good electrical contact. (Figure below)</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The cells are wired in series with metal ribbons. For charging 12 V batteries, 36 cells at approximately 0.5 V are vacuum laminated between glass, and a polymer metal back. The glass may have a textured surface to help trap light.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03448.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img src="http://sub.allaboutcircuits.com/images/03448.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Silicon Solar cell</span></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The ultimate commercial high efficiency (21.5%) single crystal silicon solar cells have all contacts on the back of the cell. The active area of the cell is increased by moving the top (-) contact conductors to the back of the cell. The top (-) contacts are normally made to the N-type silicon on top of the cell. In Figure below the (-) contacts are made to N</span></span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">+</span></span></sup><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> diffusions on the bottom interleaved with (+) contacts. The top surface is textured to aid in trapping light within the cell.. [VSW]</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03452.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="117" src="http://sub.allaboutcircuits.com/images/03452.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">High efficiency solar cell with all contacts on the back. Adapted from Figure 1 [VSW]</span></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Multicyrstalline silicon cells</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> start out as molten silicon cast into a rectangular mold. As the silicon cools, it crystallizes into a few large (mm to cm sized) randomly oriented crystals instead of a single one. The remainder of the process is the same as for single crystal cells. The finished cells show lines dividing the individual crystals, as if the cells were cracked. The high efficiency is not quite as high as single crystal cells due to losses at crystal grain boundaries. The cell surface cannot be roughened by etching due to the random orientation of the crystals. However, an antireflectrive coating improves efficiency. These cells are competitive for all but space applications.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Three layer cell</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">: The highest efficiency solar cell is a stack of three cells tuned to absorb different portions of the solar spectrum. Though three cells can be stacked atop one another, a monolithic single crystal structure of 20 semiconductor layers is more compact. At 32 % efficiency, it is now (2007) favored over silicon for space application. The high cost prevents it from finding many earth bound applications other than concentrators based on lenses or mirrors.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Intensive research has recently produced a version enhanced for terrestrial concentrators at 400 - 1000 suns and 40.7% efficiency. This requires either a big inexpensive Fresnel lens or reflector and a small area of the expensive semiconductor. This combination is thought to be competitive with inexpensive silicon cells for solar power plants. [RRK] [LZy]</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Metal organic chemical vapor deposition (MOCVD)</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> deposits the layers atop a P-type germanium substrate. The top layers of N and P-type gallium indium phosphide (GaInP) having a band gap of 1.85 eV, absorbs ultraviolet and visible light. These wavelengths have enough energy to exceed the band gap. Longer wavelengths (lower energy) do not have enough energy to create electron-hole pairs, and pass on through to the next layer. A gallium arsenide layers having a band gap of 1.42 eV, absorbs near infrared light. Finally the germanium layer and substrate absorb far infrared. The series of three cells produce a voltage which is the sum of the voltages of the three cells. The voltage developed by each material is 0.4 V less than the band gap energy listed in Table below. For example, for GaInP: 1.8 eV/e - 0.4 V = 1.4 V. For all three the voltage is 1.4 V + 1.0 V + 0.3 V = 2.7 V. [BRB]</span></span></div><a href="" name="3layercell.tbl" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><br />
<a href="" name="3layercell.tbl" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">High efficiency triple layer solar cell.</span></span></i></div></a><br />
<table border="1" style="background-color: lightcyan; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><tbody style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <th style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Layer</span></th> <th style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Band gap</span></th> <th style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Light absorbed</span></th> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Gallium indium phosphide</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">1.8 eV</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">UV, visible</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Gallium arsenide</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">1.4 eV</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">near infrared</span></td> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Germanium</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">0.7 eV</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">far infrared</span></td></tr>
</tbody></table><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Crystalline solar cell arrays have a long useable life. Many arrays are guaranteed for 25 years, and believed to be good for 40 years. They do not suffer initial degradation compared with amorphous silicon.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Both single and multicrystalline solar cells are based on silicon wafers. The silicon is both the substrate and the active device layers. Much silicon is consumed. This kind of cell has been around for decades, and takes approximately 86% of the solar electric market. For further information about crystalline solar cells see Honsberg. [CHS]</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Amorphous silicon</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> thin film solar cells use tiny amounts of the active raw material, silicon. Approximately half the cost of conventional crystalline solar cells is the solar cell grade silicon. The thin film deposition process reduces this cost. The downside is that efficiency is about half that of conventional crystalline cells. Moreover, efficiency degrades by 15-35% upon exposure to sunlight. A 7% efficient cell soon ages to 5% efficiency. Thin film amorphous silicon cells work better than crystalline cells in dim light. They are put to good use in solar powered calculators.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Non-silicon based solar cells make up about 7% of the market. These are thin-film polycrystalline products. Various compound semiconductors are the subject of research and development. Some non-silicon products are in production. Generally, the efficiency is better than amorphous silicon, but not nearly as good as crystalline silicon.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Cadmium telluride</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> as a polycrystalline thin film on metal or glass can have a higher efficiency than amorphous silicon thin films. If deposited on metal, that layer is the negative contact to the cadmium telluride thin film. The transparent P-type cadmium sulfide atop the cadmium telluride serves as a buffer layer. The positive top contact is transparent, electrically conductive fluorine doped tin oxide. These layers may be laid down on a sacrificial foil in place of the glass in the process in the following pargraph. The sacrificial foil is removed after the cell is mounted to a permanent substrate.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03449.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="87" src="http://sub.allaboutcircuits.com/images/03449.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Cadmium telluride solar cell on glass or metal.</span></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">A process for depositing cadmium telluride on glass begins with the deposition of N-type transparent, electrically conducive, tin oxide on a glass substrate. The next layer is P-type cadmium telluride; though, N-type or intrinsic may be used. These two layers constitute the NP junction. A P</span></span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">+</span></span></sup><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> (heavy P-type) layer of lead telluride aids in establishing a low resistance contact. A metal layer makes the final contact to the lead telluride. These layers may be laid down by vacuum deposition, chemical vapor deposition (CVD), screen printing, electrodeposition, or atmospheric pressure chemical vapor deposition (APCVD) in helium. [KWM]</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">A variation of cadmium telluride is mercury cadmium telluride. Having lower bulk resistance and lower contact resistance improves efficiency over cadmium telluride.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03450.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="99" src="http://sub.allaboutcircuits.com/images/03450.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Cadmium Indium Gallium diSelenide solar cell (CIGS)</span></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Cadmium Indium Gallium diSelenide</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">: A most promising thin film solar cell at this time (2007) is manufactured on a ten inch wide roll of flexible polyimide– Cadmium Indium Gallium diSelenide (CIGS). It has a spectacular efficiency of 10%. Though, commercial grade crystalline silicon cells surpassed this decades ago, CIGS should be cost competitive. The deposition processes are at a low enough temperature to use a polyimide polymer as a substrate instead of metal or glass. (Figure above) The CIGS is manufactured in a roll to roll process, which should drive down costs. GIGS cells may also be produced by an inherently low cost electrochemical process. [EET]</span></span></div><ul style="margin-bottom: 10px; margin-left: 20px; margin-right: 20px; margin-top: 10px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><li style="margin-bottom: 0px; margin-left: 10px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <b style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">REVIEW</span></span></b><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">:</span></span></li>
<li style="margin-bottom: 0px; margin-left: 10px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Most solar cells are silicon single crystal or multicrystal because of their good efficiency and moderate cost.</span></span></li>
<li style="margin-bottom: 0px; margin-left: 10px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Less efficient thin films of various amorphous or polycrystalline materials comprise the rest of the market.</span></span></li>
<li style="margin-bottom: 0px; margin-left: 10px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Table below compares selected solar cells.</span></span></li>
</ul><a href="" name="solarcell.tbl" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><br />
<a href="" name="solarcell.tbl" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Solar cell properties</span></span></i></div></a><br />
<table border="1" style="background-color: lightcyan; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><tbody style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <th style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Solar cell type</span></th> <th style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Maximum efficiency</span></th> <th style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Practical efficiency</span></th> <th style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Notes</span></th> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Selenium, polycrystalline</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">0.7%</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">-</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">1883, Charles Fritts</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Silicon, single crystal</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">-</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">4%</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">1950's, first silicon solar cell</span></td> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Silicon, single crystal PERL, terrestrial, space</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">25%</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">-</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">solar cars, cost=100x commercial</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Silicon, single crystal, commercial terrestrial</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">24%</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">14-17%</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">$5-$10/peak watt</span></td> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Cypress Semiconductor, Sunpower, silicon single crystal</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">21.5%</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">19%</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">all contacts on cell back</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Gallium Indium Phosphide/ Gallium Arsenide/ Germanium, single crystal, multilayer</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">-</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">32%</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Preferred for space.</span></td> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Advanced terrestrial version of above.</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">-</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">40.7%</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Uses optical concentrator.</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Silicon, multicrystalline</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">18.5%</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">15.5%</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">-</span></td> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Thin films,</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">-</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">-</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">-</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Silicon, amorphous</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">13%</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">5-7%</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Degrades in sun light. Good indoors for calculators or cloudy outdoors.</span></td> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Cadmium telluride, polycrystalline</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">16%</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">-</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">glass or metal substrate</span></td></tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Copper indium arsenide diselenide, polycrystalline</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">18%</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">10%</span></td> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">10 inch flexible polymer web. [NTH]</span></td> </tr>
<tr style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Organic polymer, 100% plastic</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">4.5%</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">-</span></td><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R&D project</span></td></tr>
</tbody></table><h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Varicap or varactor diodes</span></span></u></h3><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Diode, hot carrier" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Varicap diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Diode, varicap" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Varactor diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Diode, varactor" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">A variable capacitance diode is known as a </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">varicap diode</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> or as a </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">varactor</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">. If a diode is reverse biased, an insulating depletion region forms between the two semiconductive layers. In many diodes the width of the depletion region may be changed by varying the reverse bias. This varies the capacitance. This effect is accentuated in varicap diodes. The schematic symbols is shown in Figure below, one of which is packaged as common cathode dual diode.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03456.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="49" src="http://sub.allaboutcircuits.com/images/03456.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Varicap diode: Capacitance varies with reverse bias. This varies the frequency of a resonant network.</span></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">If a varicap diode is part of a resonant circuit as in Figure above, the frequency my be varied with a control voltage, V</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">control</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">. A large capacitance, low X</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">c</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">, in series with the varicap prevents V</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">control</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> from being shorted out by inductor L. As long as the series capacitor is large, it has minimal effect on the frequency of resonant circuit. C</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">optional</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> may be used to set the center resonant frequency. V</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">control</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> can then vary the frequency about this point. Note that the required active circuitry to make the resonant network oscillate is not shown. For an example of a varicap diode tuned AM radio receiver see "electronic varicap diode tuning," Ch 9</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Some varicap diodes may be referred to as abrupt, hyperabrupt, or super hyper abrupt. These refer to the change in junction capacitance with changing reverse bias as being abrupt or hyper-abrupt, or super hyperabrupt. These diodes offer a relatively large change in capacitance. This is useful when oscillators or filters are swept over a large frequency range. Varying the bias of abrupt varicaps over the rated limits, changes capacitance by a 4:1 ratio, hyperabrupt by 10:1, super hyperabrupt by 20:1.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Varactor diodes may be used in frequency multiplier circuits. See "Practical analog semiconductor circuits," Varactor multiplier</span></span></div><h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Snap diode</span></span></u></h3><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Snap diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Step recovery diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Diode, snap" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">snap diode</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">, also known as the </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">step recovery diode</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> is designed for use in high ratio frequency multipliers up to 20 gHz. When the diode is forward biased, charge is stored in the PN junction. This charge is drawn out as the diode is reverse biased. The diode looks like a low impedance current source during forward bias. When reverse bias is applied it still looks like a low impedance source until all the charge is withdrawn. It then "snaps" to a high impedance state causing a voltage impulse, rich in harmonics. An applications is a comb generator, a generator of many harmonics. Moderate power 2x and 4x multipliers are another application.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="pindiode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">PIN diodes</span></span></u></h3><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="PIN diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Diode, pin" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">A </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">PIN diode</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> is a fast low capacitance switching diode. Do not confuse a PIN switching diode with a PIN photo diode. A PIN diode is manufactured like a silicon switching diode with an intrinsic region added between the PN junction layers. This yields a thicker depletion region, the insulating layer at the junction of a reverse biased diode. This results in lower capacitance than a reverse biased switching diode.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03460.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="119" src="http://sub.allaboutcircuits.com/images/03460.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Pin diode: Cross section aligned with schematic symbol.</span></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">PIN diodes are used in place of switching diodes in radio frequency (RF) applications, for example, a T/R. The 1n4007 1000 V, 1 A general purpose power diode is reported to be useable as a PIN switching diode. The high voltage rating of this diode is achieved by the inclusion of an intrinsic layer dividing the PN junction. This intrinsic layer makes the 1n4007 a PIN diode. Another PIN diode application is a the antenna for a direction finder receiver.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">PIN diodes serve as variable resistors when the forward bias is varied. One such application is the voltage variable attenuator. The low capacitance characteristic of PIN diodes, extends the frequency flat response of the attenuator to microwave frequencies.</span></span></div><h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">IMPATT diode</span></span></u></h3><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="IMPATT diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Diode, IMPATT" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">IMPact Avalanche Transit Time</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> diode is a high power radio frequency (RF) generator operating from 3 to 100 gHz. IMPATT diodes are fabricated from silicon, gallium arsenide, or silicon carbide.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">An IMPATT diode is reverse biased above the breakdown voltage. The high doping levels produce a thin depletion region. The resulting high electric field rapidly accelerates carriers which free other carriers in collisions with the crystal lattice. Holes are swept into the P</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">+</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> region. Electrons drift toward the N regions. The cascading effect creates an avalanche current which increases even as voltage across the junction decreases. The pulses of current lag the voltage peak across the junction. A "negative resistance" effect in conjunction with a resonant circuit produces oscillations at high power levels (high for semiconductors).</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03458.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="80" src="http://sub.allaboutcircuits.com/images/03458.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">IMPATT diode: Oscillator circuit and heavily doped P and N layers.</span></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The resonant circuit in the schematic diagram of Figure above is the lumped circuit equivalent of a waveguide section, where the IMPATT diode is mounted. DC reverse bias is applied through a choke which keeps RF from being lost in the bias supply. This may be a section of waveguide known as a bias Tee. Low power RADAR transmitters may use an IMPATT diode as a power source. They are too noisy for use in the receiver.[YMCW]</span></span></div><h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Gunn diode</span></span></u></h3><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diode, gunn</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Gunn diode</span></span></i><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">A </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">gunn diode</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> is solely composed of N-type semiconductor. As such, it is not a true diode. Figure below shows a lightly doped N</span></span><sub style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">-</span></span></sub><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> layer surrounded by heavily doped N</span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">+</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> layers. A voltage applied across the N-type gallium arsenide gunn diode creates a strong electric field across the lightly doped N</span></span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">-</span></span></sup><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> layer.</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03459.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="54" src="http://sub.allaboutcircuits.com/images/03459.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Gunn diode: Oscillator circuit and cross section of only N-type semiconductor diode.</span></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">As voltage is increased, conduction increases due to electrons in a low energy conduction band. As voltage is increased beyond the threshold of approximately 1 V, electrons move from the lower conduction band to the higher energy conduction band where they no longer contribute to conduction. In other words, as voltage increases, current decreases, a negative resistance condition. The oscillation frequency is determined by the transit time of the conduction electrons, which is inversely related to the thickness of the N</span></span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">-</span></span></sup><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> layer.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The frequency may be controlled to some extent by embedding the gunn diode into a resonant circuit. The lumped circuit equivalent shown in Figure above is actually a coaxial transmission line or waveguide. Gallium arsenide gunn diodes are available for operation from 10 to 200 gHz at 5 to 65 mw power. Gunn diodes may also serve as amplifiers. [CHW] [IAP]</span></span></div><h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Shockley diode</span></span></u></h3><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">The </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Shockley diode</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">is a 4-layer thyristor used to trigger larger thyristors. It only conducts in one direction when triggered by a voltage exceeding the </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">breakover voltage</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">, about 20 V. See "Thyristors," The Shockley Diode. The bidirectional version is called a </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">diac</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">. See "Thyristors," The DIAC.</span></span></div><h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Constant-current diodes</span></span></u></h3><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="Constant-current diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Current-limiting diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Current-regulating diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="Diode, constant-current" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">A </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">constant-current diode</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">, also known as a </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">current-limiting diode</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">, or </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">current-regulating diode</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">, does exactly what its name implies: it regulates current through it to some maximum level. The constant current diode is a two terminal version of a JFET. If we try to force more current through a constant-current diode than its current-regulation point, it simply "fights back" by dropping more voltage. If we were to build the circuit in Figure below(a) and plot diode current against diode voltage, we'd get a graph that rises at first and then levels off at the current regulation point as in Figure below(b).</span></span></div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="03299.png" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img height="56" src="http://sub.allaboutcircuits.com/images/03299.png" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;" width="200" /></span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Constant current diode: (a) Test circuit, (b) current vs voltage characteristic.</span></span></i></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">One application for a constant-current diode is to automatically limit current through an LED or laser diode over a wide range of power supply voltages as in Figure below.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Of course, the constant-current diode's regulation point should be chosen to match the LED or laser diode's optimum forward current. This is especially important for the laser diode, not so much for the LED, as regular LEDs tend to be more tolerant of forward current variations.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Another application is in the charging of small secondary-cell batteries, where a constant charging current leads to predictable charging times. Of course, large secondary-cell battery banks might also benefit from constant-current charging, but constant-current diodes tend to be very small devices, limited to regulating currents in the milliamp range.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></div><h1 style="font-size: 27px; font-weight: normal; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0.6em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Other diode technologies</span></span></h1><div><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span></div><div><div style="background-color: #ffce7b; border-bottom-color: rgb(255, 165, 0); border-bottom-style: solid; border-bottom-width: 1px; border-left-color: rgb(255, 165, 0); border-left-style: solid; border-left-width: 1px; border-right-color: rgb(255, 165, 0); border-right-style: solid; border-right-width: 1px; border-top-color: rgb(255, 165, 0); border-top-style: solid; border-top-width: 1px; font-weight: bold; margin-bottom: 1em; margin-left: 0px; margin-right: 0px; margin-top: 2em; padding-bottom: 0.5em; padding-left: 1em; padding-right: 1em; padding-top: 0.5em; text-align: center; vertical-align: middle;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span></div><h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">SiC diodes</span></span></u></h3><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diodes manufactured from silicon carbide are capable of high temperature operation to 400</span></span><sup style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">o</span></span></sup><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">C. This could be in a high temperature environment: down hole oil well logging, gas turbine engines, auto engines. Or, operation in a moderate environment at high power dissipation. Nuclear and space applications are promising as SiC is 100 times more resistant to radiation compared with silicon. SiC is a better conductor of heat than any metal. Thus, SiC is better than silicon at conducting away heat. Breakdown voltage is several kV. SiC power devices are expected to reduce electrical energy losses in the power industry by a factor of 100.</span></span></div><h3 style="font-size: 18px; font-weight: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><u style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Polymer diode</span></span></u></h3><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"><a href="" name="diode, MIM" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a><a href="" name="MIM diode" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></a></span></span><br />
<div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">Diodes based on organic chemicals have been produce using low temperature processes. Hole rich and electron rich conductive polymers may be ink jet printed in layers. Most of the research and development is of the </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">organic LED</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> (OLED). However, development of inexpensive printable organic RFID (radio frequency identification) tags is on going. In this effort, a pentacene organic rectifier has been operated at 50 MHz. Rectification to 800 MHz is a development goal. An inexpensive </span></span><i style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;">metal insulator metal</span></span></i><span class="Apple-style-span" style="color: black;"><span class="Apple-style-span" style="font-family: georgia, serif;"> (MIM) diode acting like a back-to-back zener diode clipper has been delveloped. Also, a tunnel diode like device has been fabricated.</span></span></div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><br />
</div><div style="margin-bottom: 1.5em; margin-left: 0px; margin-right: 0px; margin-top: 1.5em; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></div><div class="MsoNormal" style="line-height: normal;"><span lang="EN-US" style="font-family: 'Times New Roman', serif;">Freddy Vallenilla R, EES, SECC1</span></div></div></span></div></i></div></div></div></div></div></div></div></i></div></div></div></span></div>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com2tag:blogger.com,1999:blog-4835752522918220319.post-34034813604437015462010-07-21T21:41:00.002-04:302010-07-25T10:22:26.752-04:30Prueba<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div class="module" id="moduleEditablePage1"><div class="layout"><div class="layoutregion"><div id="g_body" style="overflow-x: auto; overflow-y: auto;"><span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span><br />
<span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><h2 style="color: #5078b4; font-family: Arial, Helvetica, sans-serif; font-size: 12pt; font-weight: bold; text-align: left; text-decoration: underline;">The PNP Transistor</h2><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">The <strong>PNP Transistor</strong> is the exact opposite to the <strong>NPN Transistor</strong> device we looked at in the previous tutorial. Basically, in this type of transistor construction the two diodes are reversed with respect to the NPN type, with the arrow, which also defines the Emitter terminal this time pointing inwards in the transistor symbol. Also, all the polarities are reversed which means that <em>PNP Transistors</em> "sink" current as opposed to the NPN transistor which "sources" current. Then, PNP Transistors use a small output base current and a negative base voltage to control a much larger emitter-collector current. The construction of a PNP transistor consists of two P-type semiconductor materials either side of the N-type material as shown below.</div><h3 style="color: #303090; font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: left; text-decoration: underline;">A PNP Transistor Configuration</h3><div><br />
</div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 9pt; text-align: left; width: 520px;"><tbody>
<tr><td style="font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><img alt="PNP Transistor Configuration" border="0" height="248" src="http://www.electronics-tutorials.ws/transistor/tran6.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="510" /></td> </tr>
<tr><td style="font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">Note: Conventional current flow.</td></tr>
</tbody></table></span><span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><br />
</span><br />
<div><span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><br />
</span><br />
<span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">The <strong>PNP Transistor</strong> has very similar characteristics to their NPN bipolar cousins, except that the polarities (or biasing) of the current and voltage directions are reversed for any one of the possible three configurations looked at in the first tutorial, Common Base, Common Emitter and Common Collector. Generally, PNP Transistors require a negative (-ve) voltage at their Collector terminal with the flow of current through the emitter-collector terminals being <b>Holes</b> as opposed to <b>Electrons</b> for the NPN types. Because the movement of holes across the depletion layer tends to be slower than for electrons, PNP transistors are generally more slower than their equivalent NPN counterparts when operating.</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">To cause the Base current to flow in a PNP transistor the Base needs to be more negative than the Emitter (current must leave the base) by approx 0.7 volts for a silicon device or 0.3 volts for a germanium device with the formulas used to calculate the Base resistor, Base current or Collector current are the same as those used for an equivalent NPN transistor and is given as.</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><img alt="Base Current Calculation" border="0" height="132" src="http://www.electronics-tutorials.ws/transistor/tran40.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="244" /></div><div align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">Generally, the PNP transistor can replace NPN transistors in electronic circuits, the only difference is the polarities of the voltages, and the directions of the current flow. PNP Transistors <span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">can also be used as switching devices and an example of a PNP transistor switch is shown below.</span></span></div><h3 style="font-size: 10pt; text-align: left;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">A PNP Transistor Circuit</span></span></h3><div><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;"><br />
</span></span></div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="font-size: inherit; width: 320px;"><tbody>
<tr><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img alt="PNP transistor Circuit" border="0" height="251" src="http://www.electronics-tutorials.ws/transistor/tran15.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="311" /><br />
<br />
</span></td></tr>
</tbody></table><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">The </span></span><b><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">Output Characteristics Curves</span></span></b><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;"> for a PNP transistor look very similar to those for an equivalent NPN transistor except that they are rotated by 180</span></span><sup><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">o</span></span></sup><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;"> to take account of the reverse polarity voltages and currents, (the currents flowing out of the Base and Collector in a PNP transistor are negative).</span></span></div><h2 style="font-size: 12pt; font-weight: normal; text-align: left;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">Transistor Matching</span></span></h2><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">You may think what is the point of having a </span></span><strong><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">PNP Transistor</span></span></strong><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">, when there are plenty of NPN Transistors available?. Well, having two different types of transistors PNP & NPN, can be an advantage when designing amplifier circuits such as </span></span><em><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">Class B Amplifiers</span></span></em><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;"> that use "Complementary" or "Matched Pair" transistors or for reversible </span></span><em><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">H-Bridge</span></span></em><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;"> motor control circuits. A pair of corresponding NPN and PNP transistors with near identical characteristics to each other are called </span></span><strong><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">Complementary Transistors</span></span></strong><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;"> for example, a TIP3055 (NPN), TIP2955 (PNP) are good examples of complementary or matched pair silicon power transistors. They have a DC current gain, </span></span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">Beta</span></span></span><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">, (</span></span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">Ic / Ib</span></span></span><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">) matched to within 10% and high Collector current of about 15A making them suitable for general motor control or robotic applications.</span></span></div><h2 style="font-size: 12pt; font-weight: normal; text-align: left;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">Identifying the PNP Transistor</span></span></h2><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">We saw in the first tutorial of this Transistors section, that transistors are basically made up of two </span></span><em><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">Diodes </span></span></em><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">connected together back-to-back. We can use this analogy to determine whether a transistor is of the type PNP or NPN by testing its </span></span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">Resistance</span></span></span><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;"> between the three different leads, </span></span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">Emitter</span></span></span><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">, </span></span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">Base</span></span></span><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;"> and </span></span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">Collector</span></span></span><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">. By testing each pair of transistor leads in both directions will result in six tests in total with the expected resistance values in Ohm's given below.</span></span></div><ul style="list-style-type: none; margin-bottom: 15px; margin-left: 15px; margin-right: 15px; margin-top: 15px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><li><span style="font-size: 11pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">1. Emitter-Base Terminals</span></span></span><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;"> - The Emitter to Base should act like a normal diode and conduct one way only.</span></span></li>
<li style="line-height: 6px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;"> </span></span></li>
<li><span style="font-size: 11pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">2. Collector-Base Terminals</span></span></span><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;"> - The Collector-Base junction should act like a normal diode and conduct one way only.</span></span></li>
<li style="line-height: 6px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;"> </span></span></li>
<li><span style="font-size: 11pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">3. Emitter-Collector Terminals</span></span></span><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;"> - The Emitter-Collector should not conduct in either direction.</span></span></li>
</ul><h3 style="font-size: 10pt; text-align: left;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;">Transistor Resistance Values for the PNP transistor and NPN transistor types</span></span></h3><div><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: black;"><br />
</span></span></div><table align="center" bgcolor="#ffffe0" border="1" cellpadding="0" cellspacing="0" style="font-size: 10pt; text-align: center; width: 480px;"><tbody>
<tr bgcolor="#d3e0ea"><td align="center" colspan="2" height="30" style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;" width="280"><span class="Apple-style-span" style="font-family: georgia, serif;">Between Transistor Terminals</span></td> <td align="center" height="30" style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;" width="100"><span class="Apple-style-span" style="font-family: georgia, serif;">PNP</span></td> <td align="center" height="30" style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;" width="100"><span class="Apple-style-span" style="font-family: georgia, serif;">NPN</span></td> </tr>
<tr><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Collector</span></td> <td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Emitter</span></td><td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">HIGH</span></sub></td><td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">HIGH</span></sub></td></tr>
<tr><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Collector</span></td><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Base</span></td> <td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">LOW</span></sub></td> <td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">HIGH</span></sub></td> </tr>
<tr><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Emitter</span></td><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Collector</span></td><td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">HIGH</span></sub></td> <td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">HIGH</span></sub></td> </tr>
<tr><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Emitter</span></td><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Base</span></td><td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">LOW</span></sub></td> <td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">HIGH</span></sub></td> </tr>
<tr><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Base</span></td><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Collector</span></td><td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">HIGH</span></sub></td> <td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">LOW</span></sub></td> </tr>
<tr><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Base</span></td><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Emitter</span></td><td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">HIGH</span></sub></td> <td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">LOW<br />
<br />
</span></sub></td></tr>
</tbody></table></span><span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><br />
</span></div></div><div class="clear" style="clear: both;"></div></div></div></div></span>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-60839667249705411222010-07-21T19:55:00.001-04:302010-07-25T10:21:42.965-04:30The NPN Transistor<div><br />
</div><span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><span style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><span style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: left;">In the previous tutorial we saw that the standard <strong>Bipolar Transistor</strong> or BJT, comes in two basic forms. An<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">NPN</span> (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">N</span>egative-<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">P</span>ositive-<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">N</span>egative) type and a <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">PNP</span> (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">P</span>ositive-<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">N</span>egative-<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">P</span>ositive) type, with the most commonly used transistor type being the <strong>NPN Transistor</strong>. We also learnt that the transistor junctions can be biased in one of three different ways - <b>Common Base</b>, <b>Common Emitter</b> and <b>Common Collector</b>. In this tutorial we will look more closely at the "Common Emitter" configuration using <strong>NPN Transistors</strong> and an example of its current flow characteristics is given below.</div><div style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: left;"><br />
</div><h3 style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: left;">An NPN Transistor Configuration</h3><div><br />
</div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="font-family: Arial, Helvetica, sans-serif; font-size: 9pt; text-align: left; width: 520px;"><tbody>
<tr><td style="font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><img alt="NPN Transistor" border="0" height="248" src="http://www.electronics-tutorials.ws/transistor/tran5.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="510" /></td> </tr>
<tr><td style="font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">Note: Conventional current flow.</td></tr>
</tbody></table><br />
<br />
<div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">We know that the transistor is a "<b>CURRENT</b>" operated device and that a large current (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ic</span>) flows freely through the device between the collector and the emitter terminals. However, this only happens when a small biasing current (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ib</span>) is flowing into the base terminal of the transistor thus allowing the base to act as a sort of current control input. The ratio of these two currents (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ic/Ib</span>) is called the <b>DC Current Gain</b> of the device and is given the symbol of <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">hfe</span> or nowadays <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Beta</span>, (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 11pt; text-align: center;">β</span>). <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Beta</span> has no units as it is a ratio. Also, the current gain from the emitter to the collector terminal, <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ic/Ie</span>, is called <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Alpha</span>, (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 11pt; text-align: center;">α</span>), and is a function of the transistor itself. As the emitter current <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ie</span> is the product of a very small base current to a very large collector current the value of this parameter <span style="font-family: Arial, Helvetica, sans-serif; font-size: 11pt; text-align: center;">α</span> is very close to unity, and for a typical low-power signal transistor this value ranges from about 0.950 to 0.999.</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><h3 style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: left;">α and β Relationships</h3><div><br />
</div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="width: 410px;"><tbody>
<tr><td style="font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><img alt="NPN Transistor Current Relationships" border="0" height="278" src="http://www.electronics-tutorials.ws/transistor/tran7.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="406" /></td> </tr>
</tbody></table></span><span style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><br />
</span><br />
<div><span style="font-family: Arial, Helvetica, sans-serif; font-size: small;"><span style="font-size: 12px;"><br />
</span></span></div><div><span style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span><br />
<span style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">By combining the two parameters <span style="font-family: Arial, Helvetica, sans-serif; font-size: 11pt; text-align: center;">α</span> and <span style="font-family: Arial, Helvetica, sans-serif; font-size: 11pt; text-align: center;">β</span> we can produce two mathematical expressions that gives the relationship between the different currents flowing in the transistor.</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="width: 280px;"><tbody>
<tr><td style="font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><img alt="Alpha and Beta Relationship" border="0" height="70" src="http://www.electronics-tutorials.ws/transistor/tran8.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="273" /></td> </tr>
</tbody></table><br />
<br />
<div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">The values of <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Beta</span> vary from about 20 for high current power transistors to well over 1000 for high frequency low power type bipolar transistors. The equation for <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Beta</span> can also be re-arranged to make <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ic</span> as the subject, and with zero base current (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ib = 0</span>) the resultant collector current <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ic</span> will also be zero, (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 11pt; text-align: center;">β</span><span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;"> x 0</span>). Also when the base current is high the corresponding collector current will also be high resulting in the base current controlling the collector current. One of the most important properties of the <strong>Bipolar Junction Transistor</strong> is that a small base current can control a much larger collector current. Consider the following example.</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><h3 style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: left;">Example No1.</h3><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">An NPN Transistor has a DC current gain, (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Beta</span>) value of 200. Calculate the base current <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ib</span> required to switch a resistive load of 4mA.</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><img alt="Base Current Calculation" border="0" height="68" src="http://www.electronics-tutorials.ws/transistor/tran9.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="270" /></div><div align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="left" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">Therefore, <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">β = 200, Ic = 4mA</span> and <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ib = 20µA</span>.</div><div align="left" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">One other point to remember about <strong>NPN Transistors</strong>. The collector voltage, (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Vc</span>) must be greater than the emitter voltage, (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ve</span>) to allow current to flow through the device between the collector-emitter junction. Also, there is a voltage drop between the base and the emitter terminal of about 0.7v for silicon devices as the input characteristics of an NPN Transistor are of a forward biased diode. Then the base voltage, (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Vbe</span>) of an NPN Transistor must be greater than this 0.7 V otherwise the transistor will not conduct with the base current given as.</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><img alt="Base Current Equation" border="0" height="65" src="http://www.electronics-tutorials.ws/transistor/tran38.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="184" /></div><div align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="left" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">Where: <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ib</span> is the base current, <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Vb</span> is the base bias voltage, <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Vbe</span> is the base-emitter volt drop (0.7v) and <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Rb</span>is the base input resistor.</div><div align="left" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><h3 style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: left;">Example No2.</h3><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">An NPN Transistor has a DC base bias voltage, <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Vb</span> of 10v and an input base resistor, <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Rb</span> of 100kΩ. What will be the value of the base current into the transistor.</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><img alt="Base Current Calculation" border="0" height="65" src="http://www.electronics-tutorials.ws/transistor/tran39.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="397" /></div><div align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="left" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">Therefore, <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ib = 93µA</span>.</div><h2 style="font-family: Arial, Helvetica, sans-serif; font-size: 12pt; font-weight: normal; text-align: left;">The Common Emitter Configuration.</h2><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">As well as being used as a switch to turn load currents "ON" or "OFF" by controlling the Base signal to the transistor, <strong>NPN Transistors</strong> can also be used to produce a circuit which will also amplify any small AC signal applied to its Base terminal. If a suitable DC "biasing" voltage is firstly applied to the transistors Base terminal thus allowing it to always operate within its linear active region, an inverting amplifier circuit called a <b>Common Emitter Amplifier</b> is produced.</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">One such <em>Common Emitter Amplifier</em> configuration is called a <em>Class A Amplifier</em>. A Class A Amplifier operation is one where the transistors Base terminal is biased in such a way that the transistor is always operating halfway between its cut-off and saturation points, thereby allowing the transistor amplifier to accurately reproduce the positive and negative halves of the AC input signal superimposed upon the DC Biasing voltage. Without this "Bias Voltage" only the positive half of the input waveform would be amplified. This type of amplifier has many applications but is commonly used in audio circuits such as pre-amplifier and power amplifier stages.</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">With reference to the common emitter configuration shown below, a family of curves known commonly as the <b>Output Characteristics Curves</b>, relates the output collector current, (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ic</span>) to the collector voltage, (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Vce</span>) when different values of base current, (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ib</span>) are applied to the transistor for transistors with the same <span style="font-family: Arial, Helvetica, sans-serif; font-size: 11pt; text-align: center;">β</span>value. A DC "Load Line" can also be drawn onto the output characteristics curves to show all the possible operating points when different values of base current are applied. It is necessary to set the initial value of<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Vce</span> correctly to allow the output voltage to vary both up and down when amplifying AC input signals and this is called setting the operating point or <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Quiescent Point</span>, <b>Q-point</b> for short and this is shown below.</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><h3 style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: left;">The Common Emitter Amplifier Circuit</h3><div><br />
</div><div><br />
</div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="width: 320px;"><tbody>
<tr><td align="center" style="font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><img alt="Common Emitter Amplifier" border="0" height="235" src="http://www.electronics-tutorials.ws/transistor/tran10.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="417" /></td> </tr>
</tbody></table><br />
<br />
<h3 style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: left;">Output Characteristics Curves for a Typical Bipolar Transistor</h3><div><br />
</div><div><br />
</div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="width: 480px;"><tbody>
<tr><td style="font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><img alt="Collector Characteristics" border="0" height="382" src="http://www.electronics-tutorials.ws/transistor/tran11.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="463" /></td> </tr>
</tbody></table></span><span style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><br />
</span></div><div><span style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><br />
</span><br />
<span style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">The most important factor to notice is the effect of <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Vce</span> upon the collector current <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ic</span> when <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Vce</span> is greater than about 1.0 volts. You can see that <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ic</span> is largely unaffected by changes in <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Vce</span> above this value and instead it is almost entirely controlled by the base current, <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ib</span>. When this happens we can say then that the output circuit represents that of a "Constant Current Source". It can also be seen from the common emitter circuit above that the emitter current <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ie</span> is the sum of the collector current, <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ic</span> and the base current, <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ib</span>, added together so we can also say that " <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ie = Ic + Ib</span> " for the common emitter configuration.</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">By using the output characteristics curves in our example above and also Ohm´s Law, the current flowing through the load resistor, (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">RL</span>), is equal to the collector current, <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ic</span> entering the transistor which inturn corresponds to the supply voltage, (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Vcc</span>) minus the voltage drop between the collector and the emitter terminals, (<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Vce</span>) and is given as:</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><img alt="Collector Current Calculation" border="0" height="68" src="http://www.electronics-tutorials.ws/transistor/tran33.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="370" /></div><div align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">Also, a <b>Load Line</b> can be drawn directly onto the graph of curves above from the point of "Saturation" when<span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Vce = 0</span> to the point of "Cut-off" when <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ic = 0</span> giving us the "Operating" or <b>Q-point</b> of the transistor. These two points are calculated as:</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><img alt="Collector Current Calculation" border="0" height="150" src="http://www.electronics-tutorials.ws/transistor/tran34.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="406" /></div><div align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">Then, the collector or output characteristics curves for <b>Common Emitter NPN Transistors</b> can be used to predict the Collector current, <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ic</span>, when given <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Vce</span> and the Base current, <span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center;">Ib</span>. A Load Line can also be constructed onto the curves to determine a suitable Operating or <b>Q-point</b> which can be set by adjustment of the base current.</div></span></div></span><br />
<div><br />
</div><div><br />
</div><div><br />
</div><div><br />
</div><div><div class="MsoNormal" style="line-height: normal;"><span lang="EN-US" style="font-family: 'Times New Roman', serif;">Freddy Vallenilla R, EES, SECC1</span></div></div>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-88547743860667459832010-07-21T19:48:00.002-04:302010-07-25T10:21:21.437-04:30The NPN Transistor<span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span><br />
<div><span class="Apple-style-span" style="font-size: 13px;"><span style="font-size: 12px;"></span></span><br />
<span class="Apple-style-span" style="font-size: 13px;"><span style="font-size: 12px;"><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The </span><strong><span class="Apple-style-span" style="font-family: georgia, serif;">PNP Transistor</span></strong><span class="Apple-style-span" style="font-family: georgia, serif;"> is the exact opposite to the </span><strong><span class="Apple-style-span" style="font-family: georgia, serif;">NPN Transistor</span></strong><span class="Apple-style-span" style="font-family: georgia, serif;"> device we looked at in the previous tutorial. Basically, in this type of transistor construction the two diodes are reversed with respect to the NPN type, with the arrow, which also defines the Emitter terminal this time pointing inwards in the transistor symbol. Also, all the polarities are reversed which means that </span><em><span class="Apple-style-span" style="font-family: georgia, serif;">PNP Transistors</span></em><span class="Apple-style-span" style="font-family: georgia, serif;"> "sink" current as opposed to the NPN transistor which "sources" current. Then, PNP Transistors use a small output base current and a negative base voltage to control a much larger emitter-collector current. The construction of a PNP transistor consists of two P-type semiconductor materials either side of the N-type material as shown below.</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><h3 style="font-size: 10pt; text-align: left;"><span class="Apple-style-span" style="font-family: georgia, serif;">A PNP Transistor Configuration</span></h3><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="font-size: 9pt; text-align: left; width: 520px;"><tbody>
<tr> <td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img alt="PNP Transistor Configuration" border="0" height="97" src="http://www.electronics-tutorials.ws/transistor/tran6.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="200" /></span></td> </tr>
<tr><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Note: Conventional current flow.</span></td></tr>
</tbody></table></span><span style="font-size: 12px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span><br />
<div><span style="font-size: 12px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span><br />
<span style="font-size: 12px;"><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The </span><strong><span class="Apple-style-span" style="font-family: georgia, serif;">PNP Transistor</span></strong><span class="Apple-style-span" style="font-family: georgia, serif;"> has very similar characteristics to their NPN bipolar cousins, except that the polarities (or biasing) of the current and voltage directions are reversed for any one of the possible three configurations looked at in the first tutorial, Common Base, Common Emitter and Common Collector. Generally, PNP Transistors require a negative (-ve) voltage at their Collector terminal with the flow of current through the emitter-collector terminals being </span><b><span class="Apple-style-span" style="font-family: georgia, serif;">Holes</span></b><span class="Apple-style-span" style="font-family: georgia, serif;"> as opposed to </span><b><span class="Apple-style-span" style="font-family: georgia, serif;">Electrons</span></b><span class="Apple-style-span" style="font-family: georgia, serif;"> for the NPN types. Because the movement of holes across the depletion layer tends to be slower than for electrons, PNP transistors are generally more slower than their equivalent NPN counterparts when operating.</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">To cause the Base current to flow in a PNP transistor the Base needs to be more negative than the Emitter (current must leave the base) by approx 0.7 volts for a silicon device or 0.3 volts for a germanium device with the formulas used to calculate the Base resistor, Base current or Collector current are the same as those used for an equivalent NPN transistor and is given as.</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img alt="Base Current Calculation" border="0" height="132" src="http://www.electronics-tutorials.ws/transistor/tran40.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="244" /></span></div><div align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Generally, the PNP transistor can replace NPN transistors in electronic circuits, the only difference is the polarities of the voltages, and the directions of the current flow. PNP Transistors can also be used as switching devices and an example of a PNP transistor switch is shown below.</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><h3 style="font-size: 10pt; text-align: left;"><span class="Apple-style-span" style="font-family: georgia, serif;">A PNP Transistor Circuit</span></h3><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="width: 320px;"><tbody>
<tr><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img alt="PNP transistor Circuit" border="0" height="251" src="http://www.electronics-tutorials.ws/transistor/tran15.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="311" /><br />
<br />
</span></td></tr>
</tbody></table><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The </span><b><span class="Apple-style-span" style="font-family: georgia, serif;">Output Characteristics Curves</span></b><span class="Apple-style-span" style="font-family: georgia, serif;"> for a PNP transistor look very similar to those for an equivalent NPN transistor except that they are rotated by 180</span><sup><span class="Apple-style-span" style="font-family: georgia, serif;">o</span></sup><span class="Apple-style-span" style="font-family: georgia, serif;"> to take account of the reverse polarity voltages and currents, (the currents flowing out of the Base and Collector in a PNP transistor are negative).</span></div><h2 style="font-size: 12pt; text-align: left;"><span class="Apple-style-span" style="font-family: georgia, serif;">Transistor Matching</span></h2><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">You may think what is the point of having a </span><strong><span class="Apple-style-span" style="font-family: georgia, serif;">PNP Transistor</span></strong><span class="Apple-style-span" style="font-family: georgia, serif;">, when there are plenty of NPN Transistors available?. Well, having two different types of transistors PNP & NPN, can be an advantage when designing amplifier circuits such as </span><em><span class="Apple-style-span" style="font-family: georgia, serif;">Class B Amplifiers</span></em><span class="Apple-style-span" style="font-family: georgia, serif;"> that use "Complementary" or "Matched Pair" transistors or for reversible </span><em><span class="Apple-style-span" style="font-family: georgia, serif;">H-Bridge</span></em><span class="Apple-style-span" style="font-family: georgia, serif;"> motor control circuits. A pair of corresponding NPN and PNP transistors with near identical characteristics to each other are called </span><strong><span class="Apple-style-span" style="font-family: georgia, serif;">Complementary Transistors</span></strong><span class="Apple-style-span" style="font-family: georgia, serif;"> for example, a TIP3055 (NPN), TIP2955 (PNP) are good examples of complementary or matched pair silicon power transistors. They have a DC current gain, </span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Beta</span></span><span class="Apple-style-span" style="font-family: georgia, serif;">, (</span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Ic / Ib</span></span><span class="Apple-style-span" style="font-family: georgia, serif;">) matched to within 10% and high Collector current of about 15A making them suitable for general motor control or robotic applications.</span></div><h2 style="font-size: 12pt; text-align: left;"><span class="Apple-style-span" style="font-family: georgia, serif;">Identifying the PNP Transistor</span></h2><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">We saw in the first tutorial of this Transistors section, that transistors are basically made up of two </span><em><span class="Apple-style-span" style="font-family: georgia, serif;">Diodes </span></em><span class="Apple-style-span" style="font-family: georgia, serif;">connected together back-to-back. We can use this analogy to determine whether a transistor is of the type PNP or NPN by testing its </span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Resistance</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> between the three different leads, </span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Emitter</span></span><span class="Apple-style-span" style="font-family: georgia, serif;">, </span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Base</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> and </span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Collector</span></span><span class="Apple-style-span" style="font-family: georgia, serif;">. By testing each pair of transistor leads in both directions will result in six tests in total with the expected resistance values in Ohm's given below.</span></div><ul style="list-style-type: none; margin-bottom: 15px; margin-left: 15px; margin-right: 15px; margin-top: 15px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><li><span style="font-size: 11pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">1. Emitter-Base Terminals</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> - The Emitter to Base should act like a normal diode and conduct one way only.</span></li>
<li style="line-height: 6px;"><span class="Apple-style-span" style="font-family: georgia, serif;"> </span></li>
<li><span style="font-size: 11pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">2. Collector-Base Terminals</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> - The Collector-Base junction should act like a normal diode and conduct one way only.</span></li>
<li style="line-height: 6px;"><span class="Apple-style-span" style="font-family: georgia, serif;"> </span></li>
<li><span style="font-size: 11pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">3. Emitter-Collector Terminals</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> - The Emitter-Collector should not conduct in either direction.</span></li>
</ul><h3 style="font-size: 10pt; text-align: left;"><span class="Apple-style-span" style="font-family: georgia, serif;">Transistor Resistance Values for the PNP transistor and NPN transistor types</span></h3><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><table align="center" bgcolor="#ffffe0" border="1" cellpadding="0" cellspacing="0" style="font-size: 10pt; text-align: center; width: 480px;"><tbody>
<tr bgcolor="#d3e0ea"><td align="center" colspan="2" height="30" style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;" width="280"><span class="Apple-style-span" style="font-family: georgia, serif;">Between Transistor Terminals</span></td><td align="center" height="30" style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;" width="100"><span class="Apple-style-span" style="font-family: georgia, serif;">PNP</span></td><td align="center" height="30" style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;" width="100"><span class="Apple-style-span" style="font-family: georgia, serif;">NPN</span></td></tr>
<tr><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Collector</span></td> <td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Emitter</span></td><td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">HIGH</span></sub></td><td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">HIGH</span></sub></td></tr>
<tr><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Collector</span></td><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Base</span></td> <td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">LOW</span></sub></td> <td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">HIGH</span></sub></td> </tr>
<tr><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Emitter</span></td><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Collector</span></td><td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">HIGH</span></sub></td> <td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">HIGH</span></sub></td> </tr>
<tr><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Emitter</span></td><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Base</span></td><td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">LOW</span></sub></td> <td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">HIGH</span></sub></td> </tr>
<tr><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Base</span></td><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Collector</span></td><td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">HIGH</span></sub></td> <td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">LOW</span></sub></td> </tr>
<tr><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Base</span></td><td align="center" style="font-size: 10pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Emitter</span></td><td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">HIGH</span></sub></td> <td align="center" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">R</span><sub><span class="Apple-style-span" style="font-family: georgia, serif;">LOW<br />
</span></sub></td></tr>
</tbody></table></span></div></span></div><div><br />
</div><div><br />
</div><div><br />
</div><div><div class="MsoNormal" style="line-height: normal;"><span lang="EN-US" style="font-family: 'Times New Roman', serif;">Freddy Vallenilla R, EES, SECC1</span></div></div>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-66138389399966223282010-07-21T19:39:00.002-04:302010-07-25T10:20:59.079-04:30The Schottky barrier diode<span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span><br />
<div><span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div align="justify" style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">The Schottky diode or Schottky Barrier diode is an electronics component that is widely used for radio frequency (RF) applications as a mixer or detector diode. </span></div><div align="justify" style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">The Schottky diode is also used in power applications as a rectifier, again because of its low forward voltage drop leading to lower levels of power loss compared to ordinary PN junction diodes. Although normally called the Schottky diode these days, named after Schottky, it is also sometimes referred to as the surface barrier diode, hot carrier diode or even hot electron diode.</span></div><div align="justify" style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">Despite the fact that Schottky barrier diodes have many applications in today's high tech electronics scene, it is actually one of the oldest semiconductor devices in existence. As a metal-semiconductor devices, its applications can be traced back to before 1900 where crystal detectors, cat's whisker detectors and the like were all effectively Schottky barrier diodes.</span></div><h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-weight: normal; line-height: 1.3em; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="line-height: 18px;"><span class="Apple-style-span" style="font-size: large;"><span class="Apple-style-span" style="font-family: georgia, serif;">Structure</span></span></span></h3><div align="justify" style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">The Schottky barrier diode can be manufactured in a variety of forms. The most simple is the point contact diode where a metal wire is pressed against a clean semiconductor surface. This was how the early Cat's Whisker detectors were made, and they were found to be very unreliable, requiring frequent repositioning of the wire to ensure satisfactory operation. In fact the diode that is formed may either be a Schottky barrier diode or a standard PN junction dependent upon the way in which the wire and semiconductor meet and the resulting forming process.</span></div><div style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"></div><br />
<center style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"> <img alt="Point contact Schottky diode" src="http://www.radio-electronics.com/info/data/semicond/schottky_diode/point_contact_diode.gif" style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-color: initial; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-style: initial; border-style: initial; border-top-width: 0px; display: block; font-size: 12px; margin-bottom: 9px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;" /></center> <br />
<div style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"></div><div style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"></div><br />
<center style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"> <b style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">Point contact Schottky diode</span></b></center> <center style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"> <b style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></b></center><br />
<div style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">Although point contact diodes were manufactured many years later, these diodes were also unreliable and they were subsequently replaced by a technique in which metal was vacuum deposited.</span></div><div style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"></div><br />
<center style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"> <img alt="Deposited metal Schottky diode" src="http://www.radio-electronics.com/info/data/semicond/schottky_diode/deposited_metal_diode.gif" style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-color: initial; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-style: initial; border-style: initial; border-top-width: 0px; display: block; font-size: 12px; margin-bottom: 9px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;" /></center> <br />
<div style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"></div><div style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"></div><br />
<center style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"> <strong style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">Deposited metal Schottky barrier diode</span></strong></center> <center style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"> <strong style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></strong></center><br />
<div style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">One of the problems with the simple deposited metal diode is that breakdown effects are noticed around the edge of the metalised area. This arises from the high electric fields that are present around the edge of the plate. Leakage effects are also noticed. To overcome these problems a guard ring of P+ semiconductor fabricated using a diffusion process is used along with an oxide layer around the edge. In some instances metallic silicides may be used in place of the metal.</span></div><div style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"></div><br />
<center style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"> <img alt="Deposited metal and oxide film Schottky diode" src="http://www.radio-electronics.com/info/data/semicond/schottky_diode/metalandoxidefilm_diode.gif" style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-color: initial; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-style: initial; border-style: initial; border-top-width: 0px; display: block; font-size: 12px; margin-bottom: 9px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;" /></center> <br />
<div style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"></div><div style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"></div><br />
<center style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"> <strong style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">Deposited metal and oxide film Schottky diode</span></strong></center> <center style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"> <strong style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></strong></center><br />
<div style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">There are a number of points of interest from the fabrication process. The most critical element in the manufacturing process is to ensure a clean surface for an intimate contact of the metal with the semiconductor surface, and this is achieved chemically. The metal is normally deposited in a vacuum either by the use of evaporation or sputtering techniques. However in some instances chemical deposition is gaining some favour, and actual plating has been used although it is not generally controllable to the degree required.</span></div><div align="justify" style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">When silicides are to be used instead of a pure metal contact, this is normally achieved by depositing the metal and then heat treating to give the silicide. This process has the advantage that the reaction uses the surface silicon, and the actual junction propagates below the surface, where the silicon will not have been exposed to any contaminants. A further advantage of the whole Schottky structure is that it can be fabricated using relatively low temperature techniques, and does not generally need the high temperature steps needed in impurity diffusion.</span></div><span style="font-size: 12px; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span><br />
<h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="font-weight: normal; line-height: 18px;"><span class="Apple-style-span" style="font-size: large;"><span class="Apple-style-span" style="font-family: georgia, serif;">Characteristics</span></span></span></h3><h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="font-size: 12px; font-weight: normal; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The Schottky diode is what is called a majority carrier device. This gives it tremendous advantages in terms of speed because it does not rely on holes or electrons recombining when they enter the opposite type of region as in the case of a conventional diode. By making the devices small the normal RC type time constants can be reduced, making these diodes an order of magnitude faster than the conventional PN diodes. This factor is the prime reason why they are so popular in radio frequency applications.</span></span></h3><div align="justify" style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">The diode also has a much higher current density than an ordinary PN junction. This means that forward voltage drops are lower making the diode ideal for use in power rectification applications.</span></div><div align="justify" style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">Its main drawback is found in the level of its reverse current which is relatively high. For many uses this may not be a problem, but it is a factor which is worth watching when using it in more exacting applications.</span></div><div align="justify" style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">The overall I-V characteristic is shown below. It can be seen that the Schottky diode has the typical forward semiconductor diode characteristic, but with a much lower turn on voltage. At high current levels it levels off and is limited by the series resistance or the maximum level of current injection. In the reverse direction breakdown occurs above a certain level. The mechanism is similar to the impact ionisation breakdown in a PN junction.</span></div><span style="font-size: 12px; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span><br />
<h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="font-weight: normal; line-height: 18px;"><span class="Apple-style-span" style="font-size: large;"><span class="Apple-style-span" style="font-family: georgia, serif;">Applications</span></span></span></h3><h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 17px; font-weight: normal; line-height: 1.3em; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="font-size: 12px; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The Schottky barrier diodes are widely used in the electronics industry finding many uses as diode rectifier. Its unique properties enable it to be used in a number of applications where other diodes would not be able to provide the same level of performance. In particular it is used in areas including:</span></span></h3><ul style="font-size: 12px; line-height: 18px;"><li style="padding-bottom: 1em;"><span class="Apple-style-span" style="font-family: georgia, serif;">RF mixer and detector diode</span></li>
<li style="padding-bottom: 1em;"><span class="Apple-style-span" style="font-family: georgia, serif;">Power rectifier</span></li>
<li style="padding-bottom: 1em;"><span class="Apple-style-span" style="font-family: georgia, serif;">Power OR circuits</span></li>
<li style="padding-bottom: 1em;"><span class="Apple-style-span" style="font-family: georgia, serif;">Solar cell applications</span></li>
<li style="padding-bottom: 1em;"><span class="Apple-style-span" style="font-family: georgia, serif;">Clamp diode - especially with its use in LS TTL</span></li>
</ul><div align="justify" style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">The use in each of these applications is slightly different, sometimes focussing on different properties of the diode. Accordingly they will be addressed separately.</span></div><span style="font-size: 12px; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span><br />
<h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="font-weight: normal; line-height: 18px;"><span class="Apple-style-span" style="font-size: large;"><span class="Apple-style-span" style="font-family: georgia, serif;">Schottky diode as an RF mixer and detector diode</span></span></span></h3><h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="font-size: 12px; font-weight: normal; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The Schottky diode has come into its own for radio frequency applications because of its high switching speed and high frequency capability. In view of this Schottky barrier diodes are used in many high performance diode ring mixers. In addition to this their low turn on voltage and high frequency capability and low capacitance make them ideal as RF detectors.</span></span></h3><span style="font-size: 12px; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span><br />
<h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="font-weight: normal; line-height: 18px;"><span class="Apple-style-span" style="font-size: large;"><span class="Apple-style-span" style="font-family: georgia, serif;">Schottky diode as a power rectifier diode</span></span></span></h3><h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 17px; font-weight: normal; line-height: 1.3em; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="font-size: 12px; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Schottky barrier diodes are also used in high power applications, as rectifiers. Their high current density and low forward voltage drop mean that less power is wasted than if ordinary PN junction diodes were used. This increase in efficiency means that less heat has to be dissipated, and smaller heat sinks may be able to be incorporated in the design.</span></span></h3><span style="font-size: 12px; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span><br />
<h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="font-weight: normal; line-height: 18px;"><span class="Apple-style-span" style="font-size: large;"><span class="Apple-style-span" style="font-family: georgia, serif;">Schottky diode in power OR circuits</span></span></span></h3><h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 17px; font-weight: normal; line-height: 1.3em; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="font-size: 12px; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Schottky diodes can be used in applications where a load is driven by two separate power supplies. One example may be a mains power supply and a battery supply. In these instances it is necessary that the power from one supply does not enter the other. This can be achieved using diodes. However it is important that any voltage drop across the diodes is minimised to ensure maximum efficiency. As in many other applications, the Schottky diode is ideal for this in view of its low forward voltage drop.</span></span></h3><div align="justify" style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">Schottky diodes tend to have a high reverse leakage current. This can lead to problems with any sensing circuits that may be in use. Leakage paths into high impedance circuits can give rise to false readings. This must therefore be accommodated in the circuit design.</span></div><span style="font-size: 12px; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span><br />
<h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="font-size: small;"><span class="Apple-style-span" style="font-weight: normal; line-height: 18px;"><span class="Apple-style-span" style="font-size: large;"><span class="Apple-style-span" style="font-family: georgia, serif;">Schottky diode in solar cell applications</span></span></span><span class="Apple-style-span" style="font-size: 12px; font-weight: normal; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"> </span></span></span></h3><h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 17px; font-weight: normal; line-height: 1.3em; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="font-size: 12px; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Solar cells are typically connected to rechargeable batteries, often lead acid batteries because power may be required 24 hours a day and the Sun is not always available. Solar cells do not like the reverse charge applied and therefore a diode is required in series with the solar cells. Any voltage drop will result in a reduction in efficiency and therefore a low voltage drop diode is needed. As in other applications, the low voltage drop of the Schottky diode is particularly useful, and as a result Schottky diodes are normally used in this application.</span></span></h3><span style="font-size: 12px; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span><br />
<h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="font-weight: normal; line-height: 18px;"><span class="Apple-style-span" style="font-size: large;"><span class="Apple-style-span" style="font-family: georgia, serif;">Schottky diode as a clamp diode</span></span></span></h3><h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 17px; font-weight: normal; line-height: 1.3em; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="font-size: 12px; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Schottky barrier diodes may also be used as a clamp diode in a transistor circuit to speed the operation when used as a switch. They were used in this role in the 74LS (low power Schottky) and 74S (Schottky) families of logic circuits. Schottky barrier diodes are inserted between the collector and base of the driver transistor to act as a clamp. To produce a low or logic "0" output the transistor is driven hard on, and in this situation the base collector junction in the diode is forward biased. When the Schottky diode is present this takes most of the current and allows the turn off time of the transistor to be greatly reduced, thereby improving the speed of the circuit.</span></span></h3><div style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"></div><br />
<center style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"> <img alt="An NPN transistor with Schottky diode clamp" src="http://www.radio-electronics.com/info/data/semicond/schottky_diode/schottky-clamp-circuit.gif" style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-color: initial; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-style: initial; border-style: initial; border-top-width: 0px; display: block; font-size: 12px; margin-bottom: 9px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;" /></center> <br />
<div style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"></div><div style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"></div><br />
<center style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"> <b style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;"><span class="Apple-style-span" style="font-family: georgia, serif;">An NPN transistor with Schottky diode clamp</span></b></center> <br />
<div style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 12px; line-height: 18px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 10px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: justify; vertical-align: baseline;"></div><span style="font-size: 12px; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span><br />
<h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="font-weight: normal; line-height: 18px;"><span class="Apple-style-span" style="font-size: large;"><span class="Apple-style-span" style="font-family: georgia, serif;">Schottky diode summary</span></span></span></h3><h3 style="background-color: transparent; border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px; font-size: 17px; font-weight: normal; line-height: 1.3em; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; outline-color: initial; outline-style: initial; outline-width: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0.5em; vertical-align: baseline;"><span class="Apple-style-span" style="font-size: 12px; line-height: 18px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Schottky barrier diodes are used in many areas of electronics because of the properties thay offer. As a result Schottky diodes are used as discrete components for RF and power applications as well as being incorporated within devices as protection devices or for charge removal in devices from photodiodes to MESFETs. Not only do Schottky barrier diodes find widespread use in many applications in its own right, but it an essential part of many other components as well.</span></span></h3></span></div><div><br />
</div><div><br />
</div><div><br />
</div><div><div class="MsoNormal" style="line-height: normal;"><span lang="EN-US" style="font-family: 'Times New Roman', serif; font-size: 12pt;">Freddy Vallenilla R, EES, SECC1</span></div></div>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-13360013035886334682010-07-21T19:22:00.002-04:302010-07-25T10:20:34.810-04:30The Transistor as a Switch<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">When used as an AC signal amplifier, the transistors Base biasing voltage is applied so that it operates within its "</span><b><span class="Apple-style-span" style="font-family: georgia, serif;">Active</span></b><span class="Apple-style-span" style="font-family: georgia, serif;">" region and the linear part of the output characteristics curves are used. However, both the NPN & PNP type bipolar transistors can be made to operate as an "ON/OFF" type solid state switch for controlling high power devices such as motors, solenoids or lamps. If the circuit uses the </span><strong><span class="Apple-style-span" style="font-family: georgia, serif;">Transistor as a Switch</span></strong><span class="Apple-style-span" style="font-family: georgia, serif;">, then the biasing is arranged to operate in the output characteristics curves seen previously in the areas known as the "</span><strong><span class="Apple-style-span" style="font-family: georgia, serif;">Saturation</span></strong><span class="Apple-style-span" style="font-family: georgia, serif;">" and "</span><strong><span class="Apple-style-span" style="font-family: georgia, serif;">Cut-off</span></strong><span class="Apple-style-span" style="font-family: georgia, serif;">" regions as shown below.</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><h3 style="font-size: 10pt; text-align: left;"><span class="Apple-style-span" style="font-family: georgia, serif;">Transistor Curves</span></h3><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="font-size: 9pt; text-align: left; width: 400px;"><tbody>
<tr><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img alt="Transistor Curves for Switching" border="0" height="296" src="http://www.electronics-tutorials.ws/transistor/tran27.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="397" /></span></td> </tr>
</tbody></table><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span><br />
<div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The pink shaded area at the bottom represents the "Cut-off" region. Here the operating conditions of the transistor are zero input base current (Ib), zero output collector current (Ic) and maximum collector voltage (Vce) which results in a large depletion layer and no current flows through the device. The transistor is switched "Fully-OFF". The lighter blue area to the left represents the "Saturation" region. Here the transistor will be biased so that the maximum amount of base current is applied, resulting in maximum collector current flow and minimum collector emitter voltage which results in the depletion layer being as small as possible and maximum current flows through the device. The transistor is switched "Fully-ON". Then we can summarize this as:</span></div><ul style="font-size: 12px; list-style-type: none; margin-bottom: 15px; margin-left: 15px; margin-right: 15px; margin-top: 15px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><li><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">1. Cut-off Region</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> - Both junctions are Reverse-biased, Base current is zero or very small resulting in zero Collector current flowing, the device is switched fully "OFF".</span></li>
<li style="line-height: 6px;"><span class="Apple-style-span" style="font-family: georgia, serif;"> </span></li>
<li><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">2. Saturation Region</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> - Both junctions are Forward-biased, Base current is high enough to give a Collector-Emitter voltage of 0v resulting in maximum Collector current flowing, the device is switched fully "ON".</span></li>
</ul><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">An example of an NPN Transistor as a switch being used to operate a relay is given below. With inductive loads such as relays or solenoids a flywheel diode is placed across the load to dissipate the back EMF generated by the inductive load when the transistor switches "OFF" and so protect the transistor from damage. If the load is of a very high current or voltage nature, such as motors, heaters etc, then the load current can be controlled via a suitable relay as shown.</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><h3 style="font-size: 10pt; text-align: left;"><span class="Apple-style-span" style="font-family: georgia, serif;">Transistor Switching Circuit</span></h3><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="font-size: 12px; width: 360px;"><tbody>
<tr><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img alt="Transistor Switch" border="0" height="247" src="http://www.electronics-tutorials.ws/transistor/tran12.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="358" /></span></td> </tr>
</tbody></table><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span><br />
<div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The circuit resembles that of the </span><b><span class="Apple-style-span" style="font-family: georgia, serif;">Common Emitter</span></b><span class="Apple-style-span" style="font-family: georgia, serif;"> circuit we looked at in the previous tutorials. The difference this time is that to operate the transistor as a switch the transistor needs to be turned either fully "OFF" (Cut-off) or fully "ON" (Saturated). An ideal transistor switch would have an infinite resistance when turned "OFF" resulting in zero current flow and zero resistance when turned "ON", resulting in maximum current flow. In practice when turned "OFF", small leakage currents flow through the transistor and when fully "ON" the device has a low resistance value causing a small saturation voltage (Vce) across it. In both the Cut-off and Saturation regions the power dissipated by the transistor is at its minimum.</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">To make the Base current flow, the Base input terminal must be made more positive than the Emitter by increasing it above the 0.7 volts needed for a silicon device. By varying the Base-Emitter voltage Vbe, the Base current is altered and which in turn controls the amount of Collector current flowing through the transistor as previously discussed. When maximum Collector current flows the transistor is said to be</span><b><span class="Apple-style-span" style="font-family: georgia, serif;">Saturated</span></b><span class="Apple-style-span" style="font-family: georgia, serif;">. The value of the Base resistor determines how much input voltage is required and corresponding Base current to switch the transistor fully "ON".</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><h3 style="font-size: 10pt; text-align: left;"><span class="Apple-style-span" style="font-family: georgia, serif;">Example No1.</span></h3><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">For example, using the transistor values from the previous tutorials of: </span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">β = 200, Ic = 4mA</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> and </span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Ib = 20uA</span></span><span class="Apple-style-span" style="font-family: georgia, serif;">, find the value of the Base resistor (</span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Rb</span></span><span class="Apple-style-span" style="font-family: georgia, serif;">) required to switch the load "ON" when the input terminal voltage exceeds </span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">2.5v</span></span><span class="Apple-style-span" style="font-family: georgia, serif;">.</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="center" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img alt="Switch Example 1" border="0" height="68" src="http://www.electronics-tutorials.ws/transistor/tran13.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="405" /></span></div><div align="center" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><h3 style="font-size: 10pt; text-align: left;"><span class="Apple-style-span" style="font-family: georgia, serif;">Example No2.</span></h3><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Again using the same values, find the minimum Base current required to turn the transistor fully "ON" (Saturated) for a load that requires </span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">200mA</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> of current.</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="center" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img alt="Switch Example 2" border="0" height="62" src="http://www.electronics-tutorials.ws/transistor/tran26.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="262" /></span></div><div align="center" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Transistor switches are used for a wide variety of applications such as interfacing large current or high voltage devices like motors, relays or lamps to low voltage digital logic IC's or gates like </span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">AND</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> Gates or </span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">OR</span></span><span class="Apple-style-span" style="font-family: georgia, serif;">Gates. Here, the output from a digital logic gate is only +5v but the device to be controlled may require a 12 or even 24 volts supply. Or the load such as a DC Motor may need to have its speed controlled using a series of pulses (Pulse Width Modulation) and transistor switches will allow us to do this faster and more easily than with conventional mechanical switches.</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><h3 style="font-size: 10pt; text-align: left;"><span class="Apple-style-span" style="font-family: georgia, serif;">Digital Logic Transistor Switch</span></h3><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="font-size: 12px; width: 340px;"><tbody>
<tr><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img alt="Digital Logic Transistor Switch" border="0" height="254" src="http://www.electronics-tutorials.ws/transistor/tran41.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="328" /></span></td> </tr>
</tbody></table><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span><br />
<div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The base resistor, </span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Rb</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> is required to limit the output current of the logic gate.</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><h2 style="font-size: 12pt; font-weight: normal; text-align: left;"><span class="Apple-style-span" style="font-size: 13px;"><br />
<h3 style="font-size: 10pt; text-align: left;"><span class="Apple-style-span" style="font-family: georgia, serif;">Darlington Transistor</span></h3></span></h2><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Sometimes the DC current gain of the bipolar transistor is too low to directly switch the load current or voltage, so multiple switching transistors are used. Here, one small input transistor is used to switch "ON" or "OFF" a much larger current handling output transistor. To maximise the signal gain the two transistors are connected in a "Complementary Gain Compounding Configuration" or what is generally called a "</span><b><span class="Apple-style-span" style="font-family: georgia, serif;">Darlington Configuration</span></b><span class="Apple-style-span" style="font-family: georgia, serif;">" where the amplification factor is the product of the two individual transistors.</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><b><span class="Apple-style-span" style="font-family: georgia, serif;">Darlington Transistors</span></b><span class="Apple-style-span" style="font-family: georgia, serif;"> simply contain two individual bipolar NPN or PNP type transistors connected together so that the current gain of the first transistor is multiplied with that of the current gain of the second transistor to produce a device which acts like a single transistor with a very high current gain. The overall current gain </span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Beta (β)</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> or </span><span style="font-size: 10pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">Hfe</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> value of a Darlington device is the product of the two individual gains of the transistors and is given as:</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="center" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img alt="Darlington Transistor Current Gain" border="0" height="34" src="http://www.electronics-tutorials.ws/transistor/tran29.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="170" /></span></div><div align="center" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">So Darlington Transistors with very high </span><span style="font-size: 11pt; text-align: center;"><span class="Apple-style-span" style="font-family: georgia, serif;">β</span></span><span class="Apple-style-span" style="font-family: georgia, serif;"> values and high Collector currents are possible compared to a single transistor. An example of the two basic types of Darlington transistor are given below.</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><h3 style="font-size: 10pt; text-align: left;"><span class="Apple-style-span" style="font-family: georgia, serif;">Darlington Transistor Configurations</span></h3><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="font-size: 12px; width: 360px;"><tbody>
<tr><td style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><img alt="Darlington Transistor" border="0" height="645" src="http://www.electronics-tutorials.ws/transistor/tran14.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="342" /></span></td> </tr>
</tbody></table><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span><br />
<div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The above NPN Darlington transistor configuration shows the Collectors of the two transistors connected together with the Emitter of the first transistor connected to the Base of the second transistor therefore, the Emitter current of the first transistor becomes the Base current of the second transistor. The first or "input" transistor receives an input signal, amplifies it and uses it to drive the second or "output" transistors which amplifies it again resulting in a very high current gain. As well as its high increased current and voltage switching capabilities, another advantage of a Darlington transistor is in its high switching speeds making them ideal for use in Inverter circuits and DC motor or stepper motor control applications.</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">One difference to consider when using Darlington transistors over the conventional single bipolar transistor type is that the Base-Emitter input voltage Vbe needs to be higher at approx 1.4v for silicon devices, due to the series connection of the two PN junctions.</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div align="justify" style="font-size: 12px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Then to summarise when using a </span><strong><span class="Apple-style-span" style="font-family: georgia, serif;">Transistor as a Switch</span></strong><span class="Apple-style-span" style="font-family: georgia, serif;">.</span></div><ul style="font-family: Arial, Helvetica, sans-serif; font-size: 12px; list-style-type: none; margin-bottom: 15px; margin-left: 15px; margin-right: 15px; margin-top: 15px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><li style="list-style-type: disc; margin-bottom: 5px; margin-left: 5px; margin-right: 5px; margin-top: 5px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Transistor switches can be used to switch and control lamps, relays or even motors.</span></li>
<li style="list-style-type: disc; margin-bottom: 5px; margin-left: 5px; margin-right: 5px; margin-top: 5px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">When using bipolar transistors as switches they must be fully "OFF" or fully "ON".</span></li>
<li style="list-style-type: disc; margin-bottom: 5px; margin-left: 5px; margin-right: 5px; margin-top: 5px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Transistors that are fully "ON" are said to be in their </span><b><span class="Apple-style-span" style="font-family: georgia, serif;">Saturation</span></b><span class="Apple-style-span" style="font-family: georgia, serif;"> region.</span></li>
<li style="list-style-type: disc; margin-bottom: 5px; margin-left: 5px; margin-right: 5px; margin-top: 5px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">Transistors that are fully "OFF" are said to be in their </span><b><span class="Apple-style-span" style="font-family: georgia, serif;">Cut-off</span></b><span class="Apple-style-span" style="font-family: georgia, serif;"> region.</span></li>
<li style="list-style-type: disc; margin-bottom: 5px; margin-left: 5px; margin-right: 5px; margin-top: 5px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">In a transistor switch a small Base current controls a much larger Collector current.</span></li>
<li style="list-style-type: disc; margin-bottom: 5px; margin-left: 5px; margin-right: 5px; margin-top: 5px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">When using transistors to switch inductive relay loads a "Flywheel Diode" is required.</span></li>
<li style="list-style-type: disc; margin-bottom: 5px; margin-left: 5px; margin-right: 5px; margin-top: 5px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">When large currents or voltages need to be controlled, </span><b><span class="Apple-style-span" style="font-family: georgia, serif;">Darlington Transistors</span></b><span class="Apple-style-span" style="font-family: georgia, serif;"> are used.</span></li>
</ul></div></span><br />
<div><br />
</div><div><br />
</div><div><br />
</div><div><div class="MsoNormal" style="line-height: normal;"><span lang="EN-US" style="font-family: 'Times New Roman', serif;">Freddy Vallenilla R, EES, SECC1</span></div></div>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-60564425346643540042010-07-21T19:05:00.002-04:302010-07-25T10:19:43.567-04:30Varactors<div><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span></span><br />
<span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><div style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">A </span></span><i><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">varactor</span></span></i><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"> is also known as a </span></span><i><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">variable capacitance diode</span></span></i><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"> or a </span></span><i><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">varicap</span></span></i><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">. It provides an electrically controllable capacitance, which can be used in tuned circuits. It is small and inexpensive, which makes its use advantageous in many applications. Its disadvantages compared to a manually controlled variable capacitor are a lower Q, nonlinearity, lower voltage rating and a more limited range. Background material on varactors can be found in the Reference.</span></span></div><div style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"><br />
</span></span></div><div style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">Any PN junction has a junction capacitance that is a function of the voltage across the junction, as discussed in any account of PN junctions. The electric field in the depletion layer that is set up by the ionized donors and acceptors is responsible for the voltage difference that balances the applied voltage. A higher reverse bias widens the depletion layer, uncovering more fixed charge and raising the junction potential. The capacitance of the junction is C = Q(V)/V, and the </span></span><i><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">incremental capacitance</span></span></i><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"> is c = dQ(V)/dV. The capacitance to be used in the formula for the resonant frequency is the incremental capacitance, where it is assumed that the voltage excursions dV are small compared to V. Finite voltages give rise to nonlinearities. Efforts may be made to reduce these nonlinearities in some cases.</span></span></div><div style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"><br />
</span></span></div><div style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">The capacitance decreases as the reverse bias increases, according to the relation C = C</span></span><sub><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">o</span></span></sub><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">/(1 + V/V</span></span><sub><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">o</span></span></sub><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">)</span></span><sup><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">n</span></span></sup><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">, where C</span></span><sub><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">o</span></span></sub><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"> and V</span></span><sub><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">o</span></span></sub><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"> are constants. V</span></span><sub><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">o</span></span></sub><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"> is approximately the forward voltage of the diode. The exponent n depends on how the doping density of the semiconductors depend on distance away from the junction. For a graded junction (linear variation), n = 0.33. For an abrupt junction (constant doping density), n = 0.5. If the density jumps abruptly at the junction, then decreases (called hyperabrupt), n can be made as high as n = 2. I expect that the doping on one side of the junction is heavy, and the depletion layer is predominately on one side, but this is a constructional detail.</span></span></div><h3 style="font-size: 13pt; font-style: normal; font-weight: lighter;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">Availability of Varactors</span></span></h3><div style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">For the experiments described below, I used some varactors that were furnished by a surplus house. These were in the TO-92 package that is so convenient for experiments, and came in matched sets of three. A look in the Digi-Key catalog revealed that although a variety of varactors from Zetex are available and inexpensive, they are available only in the SOT-23 surface-mount package. This is another example of how things are becoming more difficult for those trying to learn about electronics.</span></span></div><div style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"><br />
</span></span></div><div style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><img align="right" hspace="10" src="http://mysite.du.edu/~etuttle/electron/circ361.gif" style="border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-style: initial; border-top-width: 0px;" /><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">The solution for this problem is offered by the "Surfboards" of Capital Advanced Technologies. These are small boards, as shown at the right, with SIP pins (inline pins at 0.1" spacing) and pads suitable for surface-mount devices. Discrete devices, like our SOT-23 diodes, can be easily soldered to the 6000-series Surfboards. The 6103CA, which holds one device, is suitable. The connections are shown at the right. If you buy your Surfboards from Digi-Key, you will get instructions on how to use them. The methods described here can also be used with surface-mount transistors and components, which will also fit on the Surfboards. This seems to be a practical way to use surface-mount devices when you are compelled to do so.</span></span></div><div style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"><br />
</span></span></div><div style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">I used the following tools: a 12W fine-tip soldering iron (Weller WM120); .025" dia. 60/40 rosin-core solder; fine-point tweezers; a round toothpick; clear household cement; a 10X magnifier for inspection; and, finally, a bright light. Remove the diode by pulling off the clear tape on the carrier. The SOT-23 package is seriously tiny! Make sure you can recognize top and bottom. Lay the 6103CA face-up. Put a small drop of cement on the end of the toothpick, and deposit a tiny amount at the point where the package will be attached. Then place the package on the dot of cement with the tweezers, with its feet in the proper places, and press down. This holds the package while it is being soldered, and is a step that should not be omitted. The tip of the soldering iron should be tinned. Touch the solder to the tip so that a small drop is left hanging on the tip. Now, very carefully bring the drop into contact with the pad of the package and the foil of the 6103CA board at one of the feet of the SOT-23. Capillary attraction will soon cause the solder to spread in the usual way. Press down lightly to ensure that the package is seated. This all takes only a second. Examine the joints with a 10X magnifier to make sure that the feet are entangled in the solder. It's a good idea to put a label on the back of the 6103 to identify the part, since the SOT-23 package is too small for identification.</span></span></div><h3 style="font-size: 13pt; font-style: normal; font-weight: lighter;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">Experiments</span></span></h3><div style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><img align="right" hspace="10" src="http://mysite.du.edu/~etuttle/electron/circ359.gif" style="border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-style: initial; border-top-width: 0px;" /><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">The basic circuit for testing a varactor is shown at the right. The key is the 1M resistor that isolates the DC voltage source from the circuit attached to the varactor. The 0.1μF capacitor blocks the DC bias voltage. I happened to have a 10μH inductor at hand, one of those that looks like a fat resistor, and has a reasonably high Q. The RF signal generator was coupled through a 220pF capacitor, and set for an unmodulated output. Because of stray capacitances, we cannot accurately measure the capacitance of the varactor with this circuit, but we can certainly see its action.</span></span></div><div style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">A capacitance meter did not give satisfactory results, so another method closely related to the actual application of the varactor was used. While observing the voltage across the tuned circuit with an oscilloscope, I varied the frequency looking for a maximum. From the resonant frequency, I then calculated the capacitance using the usual formula.</span></span></div><div style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><img align="left" hspace="10" src="http://mysite.du.edu/~etuttle/electron/circ360.gif" style="border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-style: initial; border-top-width: 0px;" /><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">The results of a series of measurements is shown at the left. The capacitance varied from about 170 pF at 8 V to 750 pF at 0.5V, a satisfactory range. If you plot the frequency vs. the voltage, the result is almost linear, showing that the varactor is of the hyperabrupt type, since n = 2 will give frequency proportional to voltage. I also determined that the MPN3404 that I found in the varactor drawer was probably not a varactor. It was not described, but was listed, in the Motorola data book.</span></span></div><div style="font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;">Further experiments will be described, with applications, when I obtain some more varactors.</span></span></div></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"><br />
</span></span></div></span></span></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"><br />
</span></span></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"><br />
</span></span></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"><br />
</span></span></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"><br />
</span></span></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"><br />
</span></span></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"><br />
</span></span></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"><br />
</span></span></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"><br />
</span></span></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"><br />
</span></span></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><span class="Apple-style-span" style="color: white;"><br />
</span></span></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div><div class="MsoNormal" style="line-height: normal;"><span lang="EN-US" style="font-family: 'Arial Black', sans-serif;">Freddy Vallenilla R</span></div><div class="MsoNormal" style="line-height: normal;"><span lang="EN-US" style="font-family: 'Arial Black', sans-serif;">EES SECC1</span></div></div><div><br />
</div><div><br />
</div><div><br />
</div>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0tag:blogger.com,1999:blog-4835752522918220319.post-48065927448800210852010-07-21T18:35:00.003-04:302010-07-25T10:20:09.328-04:30Prueba para formatos<div><br />
</div><div><span style="color: #333333; font-family: Arial, Helvetica, sans-serif; font-size: 14px; line-height: 18px;"></span><br />
<span style="color: #333333; font-family: Arial, Helvetica, sans-serif; font-size: 14px; line-height: 18px;"></span><br />
<span style="color: #333333; font-family: Arial, Helvetica, sans-serif; font-size: 14px; line-height: 18px;"><h4 style="font-family: Georgia, serif; font-weight: 400; letter-spacing: 0.2em; line-height: normal; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: center;"><em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">Electronic components are classed into either being Passive devices or Active devices. Active devices are different from passive devices. These devices are capable of changing their operational performance, may deliver power to the circuit, and can perform interesting mathematical functions. While a device that does not require a source of energy for its operation.</strong></em></h4><div><em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><br />
</strong></em></div><div><em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><br />
</strong></em></div><div><em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span style="font-style: normal; font-weight: normal;"></span></strong></em><br />
<em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span style="font-style: normal; font-weight: normal;"></span></strong></em><br />
<em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span style="font-style: normal; font-weight: normal;"><h2 style="font-family: Georgia, serif; font-weight: 400; line-height: normal; margin-bottom: 0.5em; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">What are Active Devices?</h2><div style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; word-wrap: break-word;"><div style="margin-bottom: 0.75em; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">An active device is any type of circuit component with the ability to electrically control electron flow (electricity controlling electricity). In order for a circuit to be properly called electronic, it must contain at least one active device. Active devices include, but are not limited to, vacuum tubes, transistors, silicon-controlled rectifiers (SCRs), and TRIACs.</div><div style="margin-bottom: 0.75em; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">All active devices control the flow of electrons through them. Some active devices allow a voltage to control this current while other active devices allow another current to do the job. Devices utilizing a static voltage as the controlling signal are, not surprisingly, called voltage-controlled devices. Devices working on the principle of one current controlling another current are known as current-controlled devices. For the record, vacuum tubes are voltage-controlled devices while transistors are made as either voltage-controlled or current controlled types. The first type of transistor successfully demonstrated was a current-controlled device.</div><div style="margin-bottom: 0.75em; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">-------------------------------------------------------------------</div><div style="margin-bottom: 0.75em; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></div><div style="margin-bottom: 0.75em; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">Electronic components are classed into either being Passive devices or Active devices. Active devices are different from passive devices. These devices are capable of changing their operational performance, may deliver power to the circuit, and can perform interesting mathematical functions. While a device that does not require a source of energy for its operation.</div><div style="margin-bottom: 0.75em; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span style="font-style: normal; font-weight: normal;"></span></strong></em></div><em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></strong></em><br />
<em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></strong></em><br />
<em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="display: inline !important; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; word-wrap: break-word;"><div style="display: inline !important; margin-bottom: 0.75em; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span style="font-style: normal; font-weight: normal;"></span></strong></em></div><em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></strong></em><br />
<em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></strong></em><br />
<em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="display: inline !important; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; word-wrap: break-word;"><em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></strong></em><br />
<em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></strong></em><br />
<em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="display: inline !important; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; word-wrap: break-word;"><div style="display: inline !important; margin-bottom: 0.75em; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">What are Active Devices?</div></div></strong></em></div></strong></em></div></strong></em><br />
<div style="margin-bottom: 0.75em; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><span style="font-style: normal; font-weight: normal;"></span></strong></em></div><em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></strong></em><br />
<em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"></strong></em><br />
<em style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><strong style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><div style="display: inline !important; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; word-wrap: break-word;"></div></strong></em><br />
<div style="margin-bottom: 0.75em; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">An active device is any type of circuit component with the ability to electrically control electron flow (electricity controlling electricity). In order for a circuit to be properly called electronic, it must contain at least one active device. Active devices include, but are not limited to, vacuum tubes, transistors, silicon-controlled rectifiers (SCRs), and TRIACs.</div><div style="margin-bottom: 0.75em; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><br />
</div><div style="margin-bottom: 0.75em; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">All active devices control the flow of electrons through them. Some active devices allow a voltage to control this current while other active devices allow another current to do the job. Devices utilizing a static voltage as the controlling signal are, not surprisingly, called voltage-controlled devices. Devices working on the principle of one current controlling another current are known as current-controlled devices. For the record, vacuum tubes are voltage-controlled devices while transistors are made as either voltage-controlled or current controlled types. The first type of transistor successfully demonstrated was a current-controlled device.</div><div style="margin-bottom: 0.75em; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"><br />
</div><div style="margin-bottom: 0.75em; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;">-------------------------------------------------------</div></div></span></strong></em></div></span></div><div><div>Electronic components are classed into either being Passive devices or Active devices. Active devices are different from passive devices. These devices are capable of changing their operational performance, may deliver power to the circuit, and can perform interesting mathematical functions. While a device that does not require a source of energy for its operation.</div><div><br />
</div><div>What are Active Devices?</div><div>An active device is any type of circuit component with the ability to electrically control electron flow (electricity controlling electricity). In order for a circuit to be properly called electronic, it must contain at least one active device. Active devices include, but are not limited to, vacuum tubes, transistors, silicon-controlled rectifiers (SCRs), and TRIACs.</div><div><br />
</div><div>All active devices control the flow of electrons through them. Some active devices allow a voltage to control this current while other active devices allow another current to do the job. Devices utilizing a static voltage as the controlling signal are, not surprisingly, called voltage-controlled devices. Devices working on the principle of one current controlling another current are known as current-controlled devices. For the record, vacuum tubes are voltage-controlled devices while transistors are made as either voltage-controlled or current controlled types. The first type of transistor successfully demonstrated was a current-controlled device.</div></div><div><br />
</div><div>-----------------------------------------------------------------</div><div><br />
</div><div><br />
</div><div><br />
</div><div><br />
</div><div><span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span><br />
<span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span><br />
<span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><h1 style="color: #5078b4; font-family: Arial, Helvetica, sans-serif; font-weight: bold; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: left;"><span style="font-size: x-large;">Field Effect Transistor</span></h1><div><br />
</div><div><br />
</div><div><br />
<div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">In the <em>Bipolar Junction Transistor</em> tutorials, we saw that the output Collector current is determined by the amount of current flowing into the Base terminal of the device and thereby making the Bipolar Transistor a <b>CURRENT</b> operated device. The <strong>Field Effect Transistor</strong>, or simply <strong>FET</strong> however, use the voltage that is applied to their input terminal to control the output current, since their operation relies on the electric field (hence the name field effect) generated by the input voltage. This then makes the <strong>Field Effect Transistor</strong> a <b>VOLTAGE</b> operated device.</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">The <strong>Field Effect Transistor</strong> is a unipolar device that has very similar properties to those of the <em>Bipolar Transistor</em> ie, high efficiency, instant operation, robust and cheap, and they can be used in most circuit applications that use the equivalent Bipolar Junction Transistors, (BJT). They can be made much smaller than an equivalent BJT transistor and along with their low power consumption and dissipation make them ideal for use in integrated circuits such as the CMOS range of chips.</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">We remember from the previous tutorials that there are two basic types of Bipolar Transistor construction,<span style="color: #5078b4; font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center; text-decoration: none;">NPN</span> and <span style="color: #5078b4; font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center; text-decoration: none;">PNP</span>, which basically describes the physical arrangement of the P-type and N-type semiconductor materials from which they are made. There are also two basic types of Field Effect Transistor, <span style="color: #5078b4; font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center; text-decoration: none;">N-channel</span> and <span style="color: #5078b4; font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center; text-decoration: none;">P-channel</span>. As their name implies, Bipolar Transistors are "Bipolar" devices because they operate with both types of charge carriers, Holes and Electrons. The Field Effect Transistor on the other hand is a "Unipolar" device that depends only on the conduction of Electrons (N-channel) or Holes (P-channel).</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">The <strong>Field Effect Transistor</strong> has one major advantage over its standard bipolar transistor cousins, in that their input impedance is very high, (Thousands of Ohms) making them very sensitive to input signals, but this high sensitivity also means that they can be easily damaged by static electricity. There are two main types of field effect transistor, the <strong>Junction Field Effect Transistor</strong> or <b>JFET</b> and the <strong>Insulated-gate Field Effect Transistor</strong> or <b>IGFET)</b>, which is more commonly known as the standard <strong>Metal Oxide Semiconductor Field Effect Transistor</strong> or <b>MOSFET</b> for short.</div></div></span></div><div><br />
</div><div><br />
</div><div><br />
</div><div>--------------------------------------------------------------</div><div><br />
</div><div><br />
</div><div><div>Field Effect Transistor</div><div><br />
</div><div><br />
</div><div>In the Bipolar Junction Transistor tutorials, we saw that the output Collector current is determined by the amount of current flowing into the Base terminal of the device and thereby making the Bipolar Transistor a CURRENT operated device. The Field Effect Transistor, or simply FET however, use the voltage that is applied to their input terminal to control the output current, since their operation relies on the electric field (hence the name field effect) generated by the input voltage. This then makes the Field Effect Transistor a VOLTAGE operated device.</div><div>The Field Effect Transistor is a unipolar device that has very similar properties to those of the Bipolar Transistor ie, high efficiency, instant operation, robust and cheap, and they can be used in most circuit applications that use the equivalent Bipolar Junction Transistors, (BJT). They can be made much smaller than an equivalent BJT transistor and along with their low power consumption and dissipation make them ideal for use in integrated circuits such as the CMOS range of chips.</div><div><br />
</div><div>We remember from the previous tutorials that there are two basic types of Bipolar Transistor construction,NPN and PNP, which basically describes the physical arrangement of the P-type and N-type semiconductor materials from which they are made. There are also two basic types of Field Effect Transistor, N-channel and P-channel. As their name implies, Bipolar Transistors are "Bipolar" devices because they operate with both types of charge carriers, Holes and Electrons. The Field Effect Transistor on the other hand is a "Unipolar" device that depends only on the conduction of Electrons (N-channel) or Holes (P-channel).</div><div><br />
</div><div>The Field Effect Transistor has one major advantage over its standard bipolar transistor cousins, in that their input impedance is very high, (Thousands of Ohms) making them very sensitive to input signals, but this high sensitivity also means that they can be easily damaged by static electricity. There are two main types of field effect transistor, the Junction Field Effect Transistor or JFET and the Insulated-gate Field Effect Transistor or IGFET), which is more commonly known as the standard Metal Oxide Semiconductor Field Effect Transistor or MOSFET for short.</div></div><div><br />
</div><div><br />
</div><div>--------------------------------------------------------------------------------------------------------------------------</div><div><br />
</div><div><br />
</div><div><span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span><br />
<span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span><br />
<span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><h1 style="font-weight: bold; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: left;"><span style="font-size: x-large;"><span style="font-family: 'times new roman', serif;"><span style="color: black;">Field Effect Transistor</span></span></span></h1><div><span style="font-family: 'times new roman', serif;"><span style="color: black;"><br />
</span></span></div><div><span style="font-family: 'times new roman', serif;"><span style="color: black;"><br />
</span></span></div><div><br />
<div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-family: 'times new roman', serif;"><span style="color: black;">In the </span></span><em><span style="font-family: 'times new roman', serif;"><span style="color: black;">Bipolar Junction Transistor</span></span></em><span style="font-family: 'times new roman', serif;"><span style="color: black;"> tutorials, we saw that the output Collector current is determined by the amount of current flowing into the Base terminal of the device and thereby making the Bipolar Transistor a </span></span><b><span style="font-family: 'times new roman', serif;"><span style="color: black;">CURRENT</span></span></b><span style="font-family: 'times new roman', serif;"><span style="color: black;"> operated device. The </span></span><strong><span style="font-family: 'times new roman', serif;"><span style="color: black;">Field Effect Transistor</span></span></strong><span style="font-family: 'times new roman', serif;"><span style="color: black;">, or simply </span></span><strong><span style="font-family: 'times new roman', serif;"><span style="color: black;">FET</span></span></strong><span style="font-family: 'times new roman', serif;"><span style="color: black;"> however, use the voltage that is applied to their input terminal to control the output current, since their operation relies on the electric field (hence the name field effect) generated by the input voltage. This then makes the </span></span><strong><span style="font-family: 'times new roman', serif;"><span style="color: black;">Field Effect Transistor</span></span></strong><span style="font-family: 'times new roman', serif;"><span style="color: black;"> a </span></span><b><span style="font-family: 'times new roman', serif;"><span style="color: black;">VOLTAGE</span></span></b><span style="font-family: 'times new roman', serif;"><span style="color: black;"> operated device.</span></span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-family: 'times new roman', serif;"><span style="color: black;">The </span></span><strong><span style="font-family: 'times new roman', serif;"><span style="color: black;">Field Effect Transistor</span></span></strong><span style="font-family: 'times new roman', serif;"><span style="color: black;"> is a unipolar device that has very similar properties to those of the </span></span><em><span style="font-family: 'times new roman', serif;"><span style="color: black;">Bipolar Transistor</span></span></em><span style="font-family: 'times new roman', serif;"><span style="color: black;"> ie, high efficiency, instant operation, robust and cheap, and they can be used in most circuit applications that use the equivalent Bipolar Junction Transistors, (BJT). They can be made much smaller than an equivalent BJT transistor and along with their low power consumption and dissipation make them ideal for use in integrated circuits such as the CMOS range of chips.</span></span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-family: 'times new roman', serif;"><span style="color: black;"><br />
</span></span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-family: 'times new roman', serif;"><span style="color: black;">We remember from the previous tutorials that there are two basic types of Bipolar Transistor construction,</span></span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span style="font-family: 'times new roman', serif;"><span style="color: black;">NPN</span></span></span><span style="font-family: 'times new roman', serif;"><span style="color: black;"> and </span></span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span style="font-family: 'times new roman', serif;"><span style="color: black;">PNP</span></span></span><span style="font-family: 'times new roman', serif;"><span style="color: black;">, which basically describes the physical arrangement of the P-type and N-type semiconductor materials from which they are made. There are also two basic types of Field Effect Transistor, </span></span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span style="font-family: 'times new roman', serif;"><span style="color: black;">N-channel</span></span></span><span style="font-family: 'times new roman', serif;"><span style="color: black;"> and </span></span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span style="font-family: 'times new roman', serif;"><span style="color: black;">P-channel</span></span></span><span style="font-family: 'times new roman', serif;"><span style="color: black;">. As their name implies, Bipolar Transistors are "Bipolar" devices because they operate with both types of charge carriers, Holes and Electrons. The Field Effect Transistor on the other hand is a "Unipolar" device that depends only on the conduction of Electrons (N-channel) or Holes (P-channel).</span></span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-family: 'times new roman', serif;"><span style="color: black;"><br />
</span></span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-family: 'times new roman', serif;"><span style="color: black;">The </span></span><strong><span style="font-family: 'times new roman', serif;"><span style="color: black;">Field Effect Transistor</span></span></strong><span style="font-family: 'times new roman', serif;"><span style="color: black;"> has one major advantage over its standard bipolar transistor cousins, in that their input impedance is very high, (Thousands of Ohms) making them very sensitive to input signals, but this high sensitivity also means that they can be easily damaged by static electricity. There are two main types of field effect transistor, the </span></span><strong><span style="font-family: 'times new roman', serif;"><span style="color: black;">Junction Field Effect Transistor</span></span></strong><span style="font-family: 'times new roman', serif;"><span style="color: black;"> or </span></span><b><span style="font-family: 'times new roman', serif;"><span style="color: black;">JFET</span></span></b><span style="font-family: 'times new roman', serif;"><span style="color: black;"> and the </span></span><strong><span style="font-family: 'times new roman', serif;"><span style="color: black;">Insulated-gate Field Effect Transistor</span></span></strong><span style="font-family: 'times new roman', serif;"><span style="color: black;"> or </span></span><b><span style="font-family: 'times new roman', serif;"><span style="color: black;">IGFET)</span></span></b><span style="font-family: 'times new roman', serif;"><span style="color: black;">, which is more commonly known as the standard </span></span><strong><span style="font-family: 'times new roman', serif;"><span style="color: black;">Metal Oxide Semiconductor Field Effect Transistor</span></span></strong><span style="font-family: 'times new roman', serif;"><span style="color: black;"> or </span></span><b><span style="font-family: 'times new roman', serif;"><span style="color: black;">MOSFET</span></span></b><span style="font-family: 'times new roman', serif;"><span style="color: black;"> for short.</span></span></div></div></span></div><div><br />
</div><div><br />
</div><div><br />
</div><div>----------------------------------------------------------------------------------------------------------------------------------</div><div><br />
</div><div><br />
</div><div><span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span><br />
<span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span><br />
<span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><h1 style="font-family: Arial, Helvetica, sans-serif; font-weight: bold; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: left;"><span style="font-size: x-large;"><span style="color: #33ffff;">Field Effect Transistor</span></span></h1><div><span style="color: #33ffff;"><br />
</span></div><div><span style="color: #33ffff;"><br />
</span></div><div><br />
<div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="color: #33ffff;">In the </span><em><span style="color: #33ffff;">Bipolar Junction Transistor</span></em><span style="color: #33ffff;"> tutorials, we saw that the output Collector current is determined by the amount of current flowing into the Base terminal of the device and thereby making the Bipolar Transistor a </span><b><span style="color: #33ffff;">CURRENT</span></b><span style="color: #33ffff;"> operated device. The </span><strong><span style="color: #33ffff;">Field Effect Transistor</span></strong><span style="color: #33ffff;">, or simply </span><strong><span style="color: #33ffff;">FET</span></strong><span style="color: #33ffff;"> however, use the voltage that is applied to their input terminal to control the output current, since their operation relies on the electric field (hence the name field effect) generated by the input voltage. This then makes the </span><strong><span style="color: #33ffff;">Field Effect Transistor</span></strong><span style="color: #33ffff;"> a </span><b><span style="color: #33ffff;">VOLTAGE</span></b><span style="color: #33ffff;"> operated device.</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="color: #33ffff;">The </span><strong><span style="color: #33ffff;">Field Effect Transistor</span></strong><span style="color: #33ffff;"> is a unipolar device that has very similar properties to those of the </span><em><span style="color: #33ffff;">Bipolar Transistor</span></em><span style="color: #33ffff;"> ie, high efficiency, instant operation, robust and cheap, and they can be used in most circuit applications that use the equivalent Bipolar Junction Transistors, (BJT). They can be made much smaller than an equivalent BJT transistor and along with their low power consumption and dissipation make them ideal for use in integrated circuits such as the CMOS range of chips.</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="color: #33ffff;"><br />
</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="color: #33ffff;">We remember from the previous tutorials that there are two basic types of Bipolar Transistor construction,</span><span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center; text-decoration: none;"><span style="color: #33ffff;">NPN</span></span><span style="color: #33ffff;"> and </span><span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center; text-decoration: none;"><span style="color: #33ffff;">PNP</span></span><span style="color: #33ffff;">, which basically describes the physical arrangement of the P-type and N-type semiconductor materials from which they are made. There are also two basic types of Field Effect Transistor, </span><span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center; text-decoration: none;"><span style="color: #33ffff;">N-channel</span></span><span style="color: #33ffff;"> and </span><span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center; text-decoration: none;"><span style="color: #33ffff;">P-channel</span></span><span style="color: #33ffff;">. As their name implies, Bipolar Transistors are "Bipolar" devices because they operate with both types of charge carriers, Holes and Electrons. The Field Effect Transistor on the other hand is a "Unipolar" device that depends only on the conduction of Electrons (N-channel) or Holes (P-channel).</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="color: #33ffff;"><br />
</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="color: #33ffff;">The </span><strong><span style="color: #33ffff;">Field Effect Transistor</span></strong><span style="color: #33ffff;"> has one major advantage over its standard bipolar transistor cousins, in that their input impedance is very high, (Thousands of Ohms) making them very sensitive to input signals, but this high sensitivity also means that they can be easily damaged by static electricity. There are two main types of field effect transistor, the </span><strong><span style="color: #33ffff;">Junction Field Effect Transistor</span></strong><span style="color: #33ffff;"> or </span><b><span style="color: #33ffff;">JFET</span></b><span style="color: #33ffff;"> and the </span><strong><span style="color: #33ffff;">Insulated-gate Field Effect Transistor</span></strong><span style="color: #33ffff;"> or </span><b><span style="color: #33ffff;">IGFET)</span></b><span style="color: #33ffff;">, which is more commonly known as the standard </span><strong><span style="color: #33ffff;">Metal Oxide Semiconductor Field Effect Transistor</span></strong><span style="color: #33ffff;"> or </span><b><span style="color: #33ffff;">MOSFET</span></b><span style="color: #33ffff;"> for short.</span></div></div></span></div><div><br />
</div><div><br />
</div><div><br />
</div><div><br />
</div><div>--------------------------------------------------------------------</div><div><br />
</div><div><span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span><br />
<span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span><br />
<span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><h1 style="font-weight: bold; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: left;"><span style="font-size: large;"><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">Field Effect Transistor</span></span></span></h1><div><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"><br />
</span></span></div><div><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"><br />
</span></span></div><div><br />
<div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">In the </span></span><em><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">Bipolar Junction Transistor</span></span></em><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"> tutorials, we saw that the output Collector current is determined by the amount of current flowing into the Base terminal of the device and thereby making the Bipolar Transistor a </span></span><b><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">CURRENT</span></span></b><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"> operated device. The </span></span><strong><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">Field Effect Transistor</span></span></strong><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">, or simply </span></span><strong><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">FET</span></span></strong><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"> however, use the voltage that is applied to their input terminal to control the output current, since their operation relies on the electric field (hence the name field effect) generated by the input voltage. This then makes the </span></span><strong><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">Field Effect Transistor</span></span></strong><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"> a </span></span><b><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">VOLTAGE</span></span></b><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"> operated device.</span></span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">The </span></span><strong><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">Field Effect Transistor</span></span></strong><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"> is a unipolar device that has very similar properties to those of the </span></span><em><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">Bipolar Transistor</span></span></em><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"> ie, high efficiency, instant operation, robust and cheap, and they can be used in most circuit applications that use the equivalent Bipolar Junction Transistors, (BJT). They can be made much smaller than an equivalent BJT transistor and along with their low power consumption and dissipation make them ideal for use in integrated circuits such as the CMOS range of chips.</span></span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"><br />
</span></span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">We remember from the previous tutorials that there are two basic types of Bipolar Transistor construction,</span></span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">NPN</span></span></span><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"> and </span></span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">PNP</span></span></span><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">, which basically describes the physical arrangement of the P-type and N-type semiconductor materials from which they are made. There are also two basic types of Field Effect Transistor, </span></span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">N-channel</span></span></span><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"> and </span></span><span style="font-size: 10pt; text-align: center; text-decoration: none;"><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">P-channel</span></span></span><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">. As their name implies, Bipolar Transistors are "Bipolar" devices because they operate with both types of charge carriers, Holes and Electrons. The Field Effect Transistor on the other hand is a "Unipolar" device that depends only on the conduction of Electrons (N-channel) or Holes (P-channel).</span></span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"><br />
</span></span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">The </span></span><strong><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">Field Effect Transistor</span></span></strong><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"> has one major advantage over its standard bipolar transistor cousins, in that their input impedance is very high, (Thousands of Ohms) making them very sensitive to input signals, but this high sensitivity also means that they can be easily damaged by static electricity. There are two main types of field effect transistor, the </span></span><strong><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">Junction Field Effect Transistor</span></span></strong><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"> or </span></span><b><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">JFET</span></span></b><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"> and the </span></span><strong><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">Insulated-gate Field Effect Transistor</span></span></strong><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"> or </span></span><b><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">IGFET)</span></span></b><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">, which is more commonly known as the standard </span></span><strong><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">Metal Oxide Semiconductor Field Effect Transistor</span></span></strong><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"> or </span></span><b><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;">MOSFET</span></span></b><span style="font-family: 'times new roman', serif;"><span style="color: #cccccc;"> for short.</span></span></div></div></span></div><div><br />
</div><div><br />
</div><div>----------------------------------------------------------------------------------------</div><div><br />
</div><div><span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span><br />
<span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span><br />
<span style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><h1 style="font-family: Arial, Helvetica, sans-serif; font-weight: bold; letter-spacing: 2px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: left;"><span style="font-size: x-large;"><span style="color: white;">Field Effect Transistor</span></span></h1><div><span style="color: white;"><br />
</span></div><div><span style="color: white;"><br />
</span></div><div><br />
<div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="color: white;">In the </span><em><span style="color: white;">Bipolar Junction Transistor</span></em><span style="color: white;"> tutorials, we saw that the output Collector current is determined by the amount of current flowing into the Base terminal of the device and thereby making the Bipolar Transistor a </span><b><span style="color: white;">CURRENT</span></b><span style="color: white;"> operated device. The </span><strong><span style="color: white;">Field Effect Transistor</span></strong><span style="color: white;">, or simply </span><strong><span style="color: white;">FET</span></strong><span style="color: white;"> however, use the voltage that is applied to their input terminal to control the output current, since their operation relies on the electric field (hence the name field effect) generated by the input voltage. This then makes the </span><strong><span style="color: white;">Field Effect Transistor</span></strong><span style="color: white;"> a </span><b><span style="color: white;">VOLTAGE</span></b><span style="color: white;"> operated device.</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="color: white;">The </span><strong><span style="color: white;">Field Effect Transistor</span></strong><span style="color: white;"> is a unipolar device that has very similar properties to those of the </span><em><span style="color: white;">Bipolar Transistor</span></em><span style="color: white;"> ie, high efficiency, instant operation, robust and cheap, and they can be used in most circuit applications that use the equivalent Bipolar Junction Transistors, (BJT). They can be made much smaller than an equivalent BJT transistor and along with their low power consumption and dissipation make them ideal for use in integrated circuits such as the CMOS range of chips.</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="color: white;"><br />
</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="color: white;">We remember from the previous tutorials that there are two basic types of Bipolar Transistor construction,</span><span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center; text-decoration: none;"><span style="color: white;">NPN</span></span><span style="color: white;"> and </span><span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center; text-decoration: none;"><span style="color: white;">PNP</span></span><span style="color: white;">, which basically describes the physical arrangement of the P-type and N-type semiconductor materials from which they are made. There are also two basic types of Field Effect Transistor, </span><span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center; text-decoration: none;"><span style="color: white;">N-channel</span></span><span style="color: white;"> and </span><span style="font-family: Arial, Helvetica, sans-serif; font-size: 10pt; text-align: center; text-decoration: none;"><span style="color: white;">P-channel</span></span><span style="color: white;">. As their name implies, Bipolar Transistors are "Bipolar" devices because they operate with both types of charge carriers, Holes and Electrons. The Field Effect Transistor on the other hand is a "Unipolar" device that depends only on the conduction of Electrons (N-channel) or Holes (P-channel).</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="color: white;"><br />
</span></div><div align="justify" style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span style="color: white;">The </span><strong><span style="color: white;">Field Effect Transistor</span></strong><span style="color: white;"> has one major advantage over its standard bipolar transistor cousins, in that their input impedance is very high, (Thousands of Ohms) making them very sensitive to input signals, but this high sensitivity also means that they can be easily damaged by static electricity. There are two main types of field effect transistor, the </span><strong><span style="color: white;">Junction Field Effect Transistor</span></strong><span style="color: white;"> or </span><b><span style="color: white;">JFET</span></b><span style="color: white;"> and the </span><strong><span style="color: white;">Insulated-gate Field Effect Transistor</span></strong><span style="color: white;"> or </span><b><span style="color: white;">IGFET)</span></b><span style="color: white;">, which is more commonly known as the standard </span><strong><span style="color: white;">Metal Oxide Semiconductor Field Effect Transistor</span></strong><span style="color: white;"> or </span><b><span style="color: white;">MOSFET</span></b><span style="color: white;"> for short.</span></div></div></span></div><div><br />
</div><div><br />
</div><div>---------------------------------------------------------------------------------</div><div><br />
</div><div><br />
</div><div><span style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span style="font-family: arial, sans-serif; font-size: 13px;"><h3 style="color: black; font-family: sans-serif; font-size: 13pt; font-style: normal; font-weight: lighter;">Varactor Theory</h3><div style="color: black; font-family: 'Times New Roman', serif; font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">A <i>varactor</i> is also known as a <i>variable capacitance diode</i> or a <i>varicap</i>. It provides an electrically controllable capacitance, which can be used in tuned circuits. It is small and inexpensive, which makes its use advantageous in many applications. Its disadvantages compared to a manually controlled variable capacitor are a lower Q, nonlinearity, lower voltage rating and a more limited range. Background material on varactors can be found in the Reference.</div><div style="color: black; font-family: 'Times New Roman', serif; font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div style="color: black; font-family: 'Times New Roman', serif; font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">Any PN junction has a junction capacitance that is a function of the voltage across the junction, as discussed in any account of PN junctions. The electric field in the depletion layer that is set up by the ionized donors and acceptors is responsible for the voltage difference that balances the applied voltage. A higher reverse bias widens the depletion layer, uncovering more fixed charge and raising the junction potential. The capacitance of the junction is C = Q(V)/V, and the <i>incremental capacitance</i> is c = dQ(V)/dV. The capacitance to be used in the formula for the resonant frequency is the incremental capacitance, where it is assumed that the voltage excursions dV are small compared to V. Finite voltages give rise to nonlinearities. Efforts may be made to reduce these nonlinearities in some cases.</div><div style="color: black; font-family: 'Times New Roman', serif; font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div style="color: black; font-family: 'Times New Roman', serif; font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">The capacitance decreases as the reverse bias increases, according to the relation C = C<sub>o</sub>/(1 + V/V<sub>o</sub>)<sup>n</sup>, where C<sub>o</sub> and V<sub>o</sub> are constants. V<sub>o</sub> is approximately the forward voltage of the diode. The exponent n depends on how the doping density of the semiconductors depend on distance away from the junction. For a graded junction (linear variation), n = 0.33. For an abrupt junction (constant doping density), n = 0.5. If the density jumps abruptly at the junction, then decreases (called hyperabrupt), n can be made as high as n = 2. I expect that the doping on one side of the junction is heavy, and the depletion layer is predominately on one side, but this is a constructional detail.</div></span></div><div><br />
</div><div><br />
</div><div><br />
</div><div>------------------------------------------------------------------------------------------------</div><div><br />
</div><div><br />
</div><div><span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><h3 style="font-family: sans-serif; font-size: 13pt; font-style: normal; font-weight: lighter;">Varactor Theory</h3><div style="font-family: 'Times New Roman', serif; font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">A <i>varactor</i> is also known as a <i>variable capacitance diode</i> or a <i>varicap</i>. It provides an electrically controllable capacitance, which can be used in tuned circuits. It is small and inexpensive, which makes its use advantageous in many applications. Its disadvantages compared to a manually controlled variable capacitor are a lower Q, nonlinearity, lower voltage rating and a more limited range. Background material on varactors can be found in the Reference.</div><div style="font-family: 'Times New Roman', serif; font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div style="font-family: 'Times New Roman', serif; font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">Any PN junction has a junction capacitance that is a function of the voltage across the junction, as discussed in any account of PN junctions. The electric field in the depletion layer that is set up by the ionized donors and acceptors is responsible for the voltage difference that balances the applied voltage. A higher reverse bias widens the depletion layer, uncovering more fixed charge and raising the junction potential. The capacitance of the junction is C = Q(V)/V, and the <i>incremental capacitance</i> is c = dQ(V)/dV. The capacitance to be used in the formula for the resonant frequency is the incremental capacitance, where it is assumed that the voltage excursions dV are small compared to V. Finite voltages give rise to nonlinearities. Efforts may be made to reduce these nonlinearities in some cases.</div><div style="font-family: 'Times New Roman', serif; font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><br />
</div><div style="font-family: 'Times New Roman', serif; font-size: 11pt; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">The capacitance decreases as the reverse bias increases, according to the relation C = C<sub>o</sub>/(1 + V/V<sub>o</sub>)<sup>n</sup>, where C<sub>o</sub> and V<sub>o</sub> are constants. V<sub>o</sub> is approximately the forward voltage of the diode. The exponent n depends on how the doping density of the semiconductors depend on distance away from the junction. For a graded junction (linear variation), n = 0.33. For an abrupt junction (constant doping density), n = 0.5. If the density jumps abruptly at the junction, then decreases (called hyperabrupt), n can be made as high as n = 2. I expect that the doping on one side of the junction is heavy, and the depletion layer is predominately on one side, but this is a constructional detail.</div></span></div><div><br />
</div><div>---------------------------------------------------------------------------------------</div><div><br />
</div><div><br />
</div><div><div>Varactor Theory</div><div><br />
</div><div>A varactor is also known as a variable capacitance diode or a varicap. It provides an electrically controllable capacitance, which can be used in tuned circuits. It is small and inexpensive, which makes its use advantageous in many applications. Its disadvantages compared to a manually controlled variable capacitor are a lower Q, nonlinearity, lower voltage rating and a more limited range. Background material on varactors can be found in the Reference.</div><div><br />
</div><div>Any PN junction has a junction capacitance that is a function of the voltage across the junction, as discussed in any account of PN junctions. The electric field in the depletion layer that is set up by the ionized donors and acceptors is responsible for the voltage difference that balances the applied voltage. A higher reverse bias widens the depletion layer, uncovering more fixed charge and raising the junction potential. The capacitance of the junction is C = Q(V)/V, and the incremental capacitance is c = dQ(V)/dV. The capacitance to be used in the formula for the resonant frequency is the incremental capacitance, where it is assumed that the voltage excursions dV are small compared to V. Finite voltages give rise to nonlinearities. Efforts may be made to reduce these nonlinearities in some cases.</div><div><br />
</div><div>The capacitance decreases as the reverse bias increases, according to the relation C = Co/(1 + V/Vo)n, where Co and Vo are constants. Vo is approximately the forward voltage of the diode. The exponent n depends on how the doping density of the semiconductors depend on distance away from the junction. For a graded junction (linear variation), n = 0.33. For an abrupt junction (constant doping density), n = 0.5. If the density jumps abruptly at the junction, then decreases (called hyperabrupt), n can be made as high as n = 2. I expect that the doping on one side of the junction is heavy, and the depletion layer is predominately on one side, but this is a constructional detail.</div></div><div><br />
</div><div><br />
</div><div><br />
</div><div>---------------------------------------------------------------------------------------------------------------------------------------------</div><div><br />
</div><div><br />
</div><div><span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><span style="font-family: 'Courier New'; font-size: small;">Varactor Devices</span></div><div><span style="font-family: 'Courier New'; font-size: small;"><br />
</span></div><div><br />
</div><div><span style="font-family: 'Courier New'; font-size: small;"></span><br />
<span style="font-family: 'Courier New'; font-size: small;"></span><br />
<span style="font-family: 'Courier New'; font-size: small;"><div style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">The VARACTOR is another of the active two-terminal diodes that operates in the microwave range. Since the basic theory of varactor operation was presented in NEETS, Module 7, <i>Introduction to Solid-State Devices and Power Supplies, Chapter 3, only a brief review of the basic principles is presented here.</i></div><div style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><i><br />
</i></div><i></i><br />
<br />
<div style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">The varactor is a semiconductor diode with the properties of a voltage-dependent capacitor. Specifically, it is a variable-capacitance, pn-junction diode that makes good use of the voltage dependency of the depletion-area capacitance of the diode.</div><div style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;">In figure 2-42, view (A), two materials are brought together to form a pn-junction diode. The different energy levels in the two materials cause a diffusion of the holes and electrons through both materials which tends to balance their energy levels. When this diffusion process stops, the diode is left with a small area on either side of the junction, called the depletion area, which contains no free electrons or holes. The movement of electrons through the materials creates an electric field across the depletion area that is described as a barrier potential and has the electrical characteristics of a charged capacitor.</div></span></div></span></div><div><br />
</div><div><br />
</div><div>-------------------------------------------------------------------------------</div><div><br />
</div><div><br />
</div><div><span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><span style="font-size: small;"><span class="Apple-style-span" style="font-family: 'times new roman', serif;">Varactor Devices</span></span></div><div><span style="font-size: small;"><span class="Apple-style-span" style="font-family: 'times new roman', serif;"><br />
</span></span></div><div><span class="Apple-style-span" style="font-family: 'times new roman', serif;"><br />
</span></div><div><span style="font-family: 'Courier New'; font-size: small;"></span><br />
<span style="font-family: 'Courier New'; font-size: small;"></span><br />
<span style="font-family: 'Courier New'; font-size: small;"><div style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: 'times new roman', serif;">The VARACTOR is another of the active two-terminal diodes that operates in the microwave range. Since the basic theory of varactor operation was presented in NEETS, Module 7, </span><i><span class="Apple-style-span" style="font-family: 'times new roman', serif;">Introduction to Solid-State Devices and Power Supplies, Chapter 3, only a brief review of the basic principles is presented here.</span></i></div><div style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><i><span class="Apple-style-span" style="font-family: 'times new roman', serif;"><br />
</span></i></div><span class="Apple-style-span" style="font-family: 'times new roman', serif;"><i></i></span><br />
<br />
<div style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: 'times new roman', serif;">The varactor is a semiconductor diode with the properties of a voltage-dependent capacitor. Specifically, it is a variable-capacitance, pn-junction diode that makes good use of the voltage dependency of the depletion-area capacitance of the diode.</span></div><div style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: 'times new roman', serif;">In figure 2-42, view (A), two materials are brought together to form a pn-junction diode. The different energy levels in the two materials cause a diffusion of the holes and electrons through both materials which tends to balance their energy levels. When this diffusion process stops, the diode is left with a small area on either side of the junction, called the depletion area, which contains no free electrons or holes. The movement of electrons through the materials creates an electric field across the depletion area that is described as a barrier potential and has the electrical characteristics of a charged capacitor.</span></div></span></div></span></div><div><br />
</div><div><br />
</div><div><br />
</div><div>---------------------------------------------------------------------------------------------------</div><div><br />
</div><div><br />
</div><div><span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"></span><br />
<span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: 13px;"><div><span style="font-size: small;"><span class="Apple-style-span" style="font-family: georgia, serif;">Varactor Devices</span></span></div><div><span style="font-size: small;"><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></span></div><div><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></div><div><span style="font-family: 'Courier New'; font-size: small;"></span><br />
<span style="font-family: 'Courier New'; font-size: small;"></span><br />
<span style="font-family: 'Courier New'; font-size: small;"><div style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The VARACTOR is another of the active two-terminal diodes that operates in the microwave range. Since the basic theory of varactor operation was presented in NEETS, Module 7, </span><i><span class="Apple-style-span" style="font-family: georgia, serif;">Introduction to Solid-State Devices and Power Supplies, Chapter 3, only a brief review of the basic principles is presented here.</span></i></div><div style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><i><span class="Apple-style-span" style="font-family: georgia, serif;"><br />
</span></i></div><span class="Apple-style-span" style="font-family: georgia, serif;"><i></i></span><br />
<br />
<div style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">The varactor is a semiconductor diode with the properties of a voltage-dependent capacitor. Specifically, it is a variable-capacitance, pn-junction diode that makes good use of the voltage dependency of the depletion-area capacitance of the diode.</span></div><div style="margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><span class="Apple-style-span" style="font-family: georgia, serif;">In figure 2-42, view (A), two materials are brought together to form a pn-junction diode. The different energy levels in the two materials cause a diffusion of the holes and electrons through both materials which tends to balance their energy levels. When this diffusion process stops, the diode is left with a small area on either side of the junction, called the depletion area, which contains no free electrons or holes. The movement of electrons through the materials creates an electric field across the depletion area that is described as a barrier potential and has the electrical characteristics of a charged capacitor.</span></div></span></div></span></div><div><br />
</div><div><br />
</div><div><br />
</div><div><span class="Apple-style-span" style="font-family: 'Times New Roman'; font-size: medium;"><img height="342" src="http://www.wenzel.com/graphics/mout5711.gif" style="border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-style: initial; border-top-width: 0px;" width="471" /></span></div><div><br />
</div><div><br />
</div><div><br />
</div><div style="text-align: center;"><span class="Apple-style-span" style="font-family: 'Times New Roman'; font-size: medium;"><img height="146" src="http://www.wenzel.com/graphics/mout5711.gif" style="border-bottom-width: 0px; border-color: initial; border-left-width: 0px; border-right-width: 0px; border-style: initial; border-top-width: 0px;" width="200" /></span></div><div><br />
</div><div><br />
</div><div><br />
</div><div><br />
</div><div><br />
</div><div><span class="Apple-style-span" style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span><br />
<span class="Apple-style-span" style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"></span><br />
<span class="Apple-style-span" style="color: #000040; font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><table align="center" bgcolor="#fafafa" border="0" cellpadding="0" cellspacing="0" style="font-size: inherit; width: 360px;"><tbody>
<tr align="center"><td style="font-family: arial, sans-serif; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px;"><img alt="N and P-Channel JFET Symbols" border="0" height="187" src="http://www.electronics-tutorials.ws/transistor/tran17.gif" style="border-bottom-color: rgb(0, 0, 0); border-bottom-width: 0px; border-color: initial; border-color: initial; border-left-color: rgb(0, 0, 0); border-left-width: 0px; border-right-color: rgb(0, 0, 0); border-right-width: 0px; border-style: initial; border-style: initial; border-top-color: rgb(0, 0, 0); border-top-width: 0px;" width="339" /><br />
<br />
</td></tr>
</tbody></table></span></div><div><br />
</div><div><br />
</div>Tecnología en Telecomunicaciones - conocimientos.com.vehttp://www.blogger.com/profile/13517798918797491823noreply@blogger.com0