A Bipolar junction transistor, shortly termed as BJT is called so as it has two PN junctions for its function. This BJT is nothing but a normal transistor. It has got two types of configurations NPN and PNP. Usually NPN transistor is preferred for the sake of convenience. The following image shows how a practical BJT looks like.

The types of BJT are NPN and PNP transistors. The NPN transistor is made by placing a ptype material between two n-type materials. The PNP transistor is made by placing an ntype material between two p-type materials.

BJT is a current controlled device. A normal transistor which we had discussed in the previous chapters come under this category. The functionality, configurations and applications are all the same.