CHARACTERISTICS OF A TRANSISTOR-1

The study of variation in current with respect to voltage in a transistor is called its characteristic. For each configuration of transistor, there are two types of characteristics:

 (i)Input characteristics

 (ii)Output characteristics

 Common base configuration

 (i)Circuit diagram

(ii)Input characteristics

 (a)  Input characteristics are obtained by plotting the emitter current IE versus emitter-base voltage VEB at constant collector base potential VCB.

(b) IE is almost independent of VCB.

 (c)Due to very low input impedance, IE increases rapidly with small increase in VEB.

 (d)IE is finite at finite value of VCB even when VEB is zero. To reduce IE to zero, the emitter must be reverse biased.

CHARACTERISTICS OF A TRANSISTOR-2

            Output characteristics:

(a)The output characteristics are obtained by plotting the collector current (IC) versus collector-base voltage (VCB) at constant emitter current (IE).

(b)IC varies with VCB  only at very low voltage (< 1 V). Transistor is not operated in this region.

 (c)As VCB increases beyond 1 volt, IC becomes independent of VCB but depends only upon the emitter current IE.

 (d)Due to high output impedance, a very large change in VCB produces a very small change in IC.

 (e)For the region to the left of VCB = 0 and for IE > 0, both emitter and collector are forward biased and it is called saturation region.

 (f)For IE < 0, both emitter and collector are reverse biased and the region is called the cut-off region.

 (g)For central region VCB > 0, the curves are parallel and it is called active region. In this region emitter is forward biased and collector is reverse biased

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