- 1. Cut-off Region - Both junctions are Reverse-biased, Base current is zero or very small resulting in zero Collector current flowing, the device is switched fully "OFF".
- 2. Saturation Region - 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".
Transistor Switching Circuit
Digital Logic Transistor Switch
Darlington Transistor Configurations
- Transistor switches can be used to switch and control lamps, relays or even motors.
- When using bipolar transistors as switches they must be fully "OFF" or fully "ON".
- Transistors that are fully "ON" are said to be in their Saturation region.
- Transistors that are fully "OFF" are said to be in their Cut-off region.
- In a transistor switch a small Base current controls a much larger Collector current.
- When using transistors to switch inductive relay loads a "Flywheel Diode" is required.
- When large currents or voltages need to be controlled, Darlington Transistors are used.