BJT

Bipolar Junction Transistor (BJT)

Current controlled

Two types NPN and PNP

both have three doped Semiconductor Regions (Base, Collector and Emitter)

BJT-symbols

You don't need to understand how semiconductors work to use them but it is helpful to understand some of their important characteristics:

• • power limits (how hot they can get)

  • gain (how much they can amplify from a input to the output, called hFE)

  • voltage limits (how high a voltage can they be used without destroying them)

  • Current limits (the amount of electron flow measured in amps be used without destroying them)

  • frequency response (what the highest speed they can go)

All the above items can be found out using manufactures data sheets on their part numbers.

Transistor (BJT) as a Switch

common transistor-packages

AC amplification

NPN transistor amp

surface mount