Operation of BJT in Active, Saturation And Cutoff Region

C=β

The transistor can be used as a switch or as an amplifier by forward/reverse biasing the emitter to base and base to collector junctions. Based on biasing, the transistor can be operated in cut off, active and saturation region of the transfer characteristics of the transistor.In this post, we will discuss operation of BJT in Active, Saturation and Cutoff Region

TRANSISTOR AS A SWITCH :

CUT OFF REGION:

In cut off region, both emitter to base and base to collector junction is in the reverse bias and no current flows through the transistor. The transistor acts as an open switch. In the saturation region, both the junctions are in forwarding bias,and the transistor acts as a closed switch.

In cut off region the output of the transistor VCE, IC, IB and IE=0

SATURATION REGION:

In the saturation region, the B-E and B-C junction are forward biased and IC=IE

ACTIVE REGION:

TRANSISTOR AS AN AMPLIFIER:

In the active region, emitter to the base junction is forward biased and the base to collector junction is reverse biased. In the active region, the transistor acts as an amplifier. In the active state, the collector current is β times the base current, i.e.,

Where,
Ic = Collector current
Ib= Base Current
β = Current gain

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