Transistors

Part 2: PNP Transistors

The PNP transistor is formed by sandwiching a layer of N-type semiconductor between two layers of P-type semiconductor.

PNP Transistor Diagram

A PNP Transistor operates in much the same fashion as an NPN transistor, but because the layers are reversed, the voltage relationships must also be reversed. Thus, both the base and collector terminals must be negative in relation to the emitter for the device to be turned on.

PNP Transistor On

 

PNP Transistor Symbol

Biasing

The base-emitter junction in both PNP and NPN transistors must be forward-biased to turn the transistor on - that is, the voltage on the P layer must be at least 0.7 volts higher than the voltage on the N layer.