A bipolar junction transistor (BJT) is a three-terminal semiconductor device used for amplifying and switching electronic signals.
A BJT consists of two p–n junctions combined together
and uses both electrons and holes as charge carriers, which is where its “bipolar” name comes from.
The three terminals are the emitter, base, and collector,
It is a current controlling device, a small current at the base controls a much larger current flowing between the collector and emitter.
There are two Type of BJT, named based on their semiconductor layer configuration.
- NPN: Two n-type regions with a p-type region in between.
- PNP: Two p-type regions with an n-type region in between.