What is the difference between BJT and NPN transister?

Answer 1

Mainly there are two types of transistors. They are BJT (Bipolar Junction Transistors) and FET(Field Effect Transisters). In BJT, there are two types called PNP and NPN. Actually NPN means a BJT transister.

Answer 2

A BJT (bipolar junction transistor) is a general term that includes both NPN and PNP transistors. An NPN transistor has a layer of P-type semiconductor sandwiched between two N-type layers, allowing current to flow from the collector to the emitter when a small current is applied to the base.