Common Collector Characteristics of BJT:
In the Common Collector Characteristics of BJT circuit arrangement of Fig. 4-31, the collector terminal is common to both input CB voltage and output CE voltage. Using this circuit, the common-collector input, output, and current gain characteristics can be determined. The output and current gain characteristics are shown in Fig. 4-32.
The common-collector output characteristics are IE plotted versus VCE for several fixed values of IB. The common-collector current gain characteristics are IE plotted versus IB for several fixed values of VCE.
It will be recalled that the common-emitter output characteristics are IE plotted against VCE, and that the common-emitter current gain characteristics are IE plotted against IB. Because IC is approximately equal to IE, the common-collector output and current gain characteristics are practically identical to those of the common-emitter circuit.
The common-collector input characteristics shown in Fig. 4-33 are quite different from either common-base or common-emitter input characteristics. The difference is due to the fact that the input voltage (VBC) is largely determined by the VEC level.
Referring to Fig. 4-31,
Increasing the level of (input voltage) VBC with VEC held constant, reduces the level of VEB, and thus reduces IB.