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 I_E plotted versus V_CE for several fixed values of I_B. The common-collector current gain characteristics are I_E plotted versus I_B for several fixed values of V_CE.

It will be recalled that the common-emitter output characteristics are I_E plotted against V_CE, and that the common-emitter current gain characteristics are I_E plotted against I_B. Because I_C is approximately equal to I_E, 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 (V_BC) is largely determined by the V_EC level.

Referring to Fig. 4-31,

Increasing the level of (input voltage) V_BC with V_EC held constant, reduces the level of V_EB, and thus reduces I_B.