Question

Explain the working principle of npn transistor

Answer 1

Forward biased causes the electron in the n-type emitter to flow toward the base. This constitutes the emitter current Ie. As these electrons flow through the p-type base, these electrons tend to combine with the holes. As the base is lightly doped and very thin,therefore,only few electrons (less than 5%) combine with holes to constitute the base current Ib. The remainder(more than 95) cross over into the collector region to constitute collector current Ic. In this way, almost the entire current flows in the collector circuit. it is clear that emitter current is the sum of the collector current and base currents. i.e.

Ie=Ib+Ic