Working principle of Transister

PNP transistor:

When common base connection of a NPN transistor.In the forward bias connection of the first PN junction ,it causes the majority charge carrier(holes) in the P-type ,flow from emitter to the base region .This constitutes the emitter current (Ie) in the transistor.As these majority carrier (hole) cross in to N-type base .They are combine with the electron .Only the few hole (i.e less than 5%) combine with the electrons ,because the base of this transistor is lightly doped and very thin .Expects those holes ,all other i.e More than 95% cross in to the collector region.This constitutes collector current (Ic). In this process ,almost the whole emitter current (holes) flows into the collector region .So in this transistor ,current conduction in the circuit is by holes.

Ie=Ic+Ib
Where ,
Ie=emitter current,
Ic=collector current and
Ib=base current

NPN transistor:
When common base connection of a NPN transistor .In the forward bias connection of the NP junction,it causes the majority charge carrier(electrons)in the N-type ,flow from emitter to the base region.This constitutes the emitter current(Ie) in the transistor.As these majority carrier(electrons)cross in to the P-type base.They are combine with the holes.Only the few electrons(i.e less than 5%) combine with the holes ,because of this transistor is lightly doped and very thin.The remainder i.e more than 95% cross into the collector region.This constitutes collector current (Ic).In this way the whole emitter current (electrons)flows into the collector region .So in this transistor, current conduction in this circuit is by electrons.