Bipolar Junction Transistor

• A BJT is a device with three terminals: collector, base, and emitter.
• In an npn-BJT, collector and emitter are made of n-type material and the base is made of p-type material.
• If the base-emitter diode becomes conducting, then a significant current can flow from collector to emitter.
• In other words, by adjusting the base-emitter voltage, the collector-emitter current can be controlled.
• This behaviour can be used to construct an amplifier.
• Also, it can be exploited to build an electrically controlled switch.