Switching With Transistor

 

Saturation: In this case the emitter junction as well as the colleetor junction are forward biased. The collector current becomes independent of the base current. In such a cas e the transistor acts like a closed switch. It is called saturation region because now colleetor current no longer depends on input current (base current).

Cut off Operation: In this type of operation the emitter and collector junctions are rcwerse biased as shown in fig. The emitter do es not emit carriers into the base. There are no carriers to be collected by the collector. The collector current is thus zero. The transistor in this case acts like an open switch.