Common emitter configuration-1

In this configuration emitter is common to input and output circuits.

(i) Circuit diagram

(ii)Input characteristics

 (a)Input characteristics are obtained by plotting the base current (IB) versus base emitter voltage (VBE) for constant collector-emitter voltage (VCE).

(b)IB increases with increase in VBE, but less rapidly as compared to common base configuration, indicating that input resistance of common emitter configuration is greater than that of common base configuration.

 (c)These characteristics resemble with those of a forward biased junction diode indicating that the base-emitter section of a transistor is essentially a junction diode.

Common emitter configuration-2

Output characteristics:

 (a)The output characteristics are obtained by plotting collector current IC versus collector-emitter voltage (VCE) at constant value of base current (IB).

(b) IC increases with increase of VCE upto 1 volt and beyond 1 volt it becomes almost constant.

 (c)The value of VCE upto which IC increases is called the knee voltage. The transistor always operates above knee voltage.

 (d)Above knee voltage, IC  is almost constant.

 (e)The region for VCE < 1 volt is called saturation region as both emitter and collector are forward biased.

 (f)In the region IB £ 0, both emitter and collector are reverse biased and it is called the cut-ff region.

 (g)The central region, where the curves are uniformly spaced and sloped, is called the active region. In this region the emitter is forward biased and the collector is reverse biased.

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