Transistor as a Switch Summary

Then to summarise when using a Transistor as a Switch.

• Transistor switches can be used to switch and control lamps, relays or even motors.
• When using the bipolar transistor as a switch they must be either “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.
• When using the transistor as a switch, a small Base current controls a much larger Collector load current.
• When using transistors to switch inductive loads such as relays and solenoids, a “Flywheel Diode” is used.
• When large currents or voltages need to be controlled, Darlington Transistors can be used.

In the next tutorial about Transistors, we will look at the operation of the junction field effect transistor known commonly as an JFET. We will also plot the output characteristics curves commonly associated with JFET amplifier circuits as a function of Source voltage to Gate voltage.