bipolar junction transistor

These components have three pins: base, collector and emitter. A little current flowing between the base and the emitter causes a larger current to flow between the collecter and the emitter. This means they can be used to amplify a signal, or as switches (cutoff and saturation states). These can be combined with resistor to create logic circuits.

Types

Bipolar junction transistors come in two flavours:

NPN transistors

In NPN transistors, the current flows from the base to the emitter.

PNP transistors

In PNP transistors, the current flows from emitter to base.

Ressources

• Transistors 101 on Adafruit