Operation of a PNP Bipolar Junction Transistor (BJT)

OPERATION OF A PNP BIPOLAR JUNCTION TRANSISTOR

The operation of a PNP transistor is similar to that of an NPN transistor. However, the current with in a PNP transistor is due to the movement of holes, whereas in an NPN transistor it is due to the movement of free electrons.

The fig.3.42 shows the PNP transistor with its emitter-base junction is forward- biased and collector base junction as reverse biased. The forward bias on the emitter base junction causes the holes in the emitter region to flow towards the base region. This constitutes the emitter current (IE). The holes after reaching in the base region, tend to combine with the electrons. If these holes combine with the electrons in the base, they constitute base current (IB). The base region is small so the most of the holes diffuse to the collector regions and constitute collector current (IC). This collector current is called injected current because this current is produced due to the holes injected from the emitter region.