Pulse and Digital Circuits

1.7 CC AMPLIFIER AS A POWER AMPLIFIER

We have seen that though an emitter follower has only unity voltage gain but its current gain is h_fc = |1 + h_fe|. This is the configuration having the largest current gain. Hence, an emitter follower can be used as a power amplifier. Consider the emitter follower using an n–p–n device, as shown in Fig. 1.47(a). There is an output only during the positive going half-cycle, i.e., during the period A.

Now consider an emitter follower using a p–n–p transistor, as shown in Fig. 1.47(b). There is an output only during the negative going half-cycle, i.e., during the period B. If n–p–n and p–n–p devices are used in an emitter follower, so that one device takes care of one half of the input cycle period and the other ...