Q. Give applications of emitter follower

The emitter follower has the following principal applications:

1. To provide current amplification with no voltage gain

2. Impedence matching

Current amplification without voltage gain : Emitter follower is a current amplifier that has no voltage gain. There are many instances where an increase in current is required but no increase in voltage is needed. In such a situation, an emitter follower can be used. Consider the two stage amplifier. Suppose this two stage amplifier has the desired voltage gain but current gain of this multistage amplifier is insufficient. In that case, we can use an emitter follower to increase the current gain without increasing the voltage gain.

Impedance matching: An emitter follower has high input impedance and low output impedance. This makes the emitter follower an ideal circuit for impedance matching. Consider an impedance matching by an emitter follower. Suppose the output impedance of the source is 120 N? while that of load is 20 ? .Emitter follower has an input impedance of 120? and output impedance of 22 ?..it is connected between high impedance source and low impedance load. The net result of this arrangement is that the maximum power is transferred from the original source to the original load. When an emitter follower is used for this purpose it is called a buffer amplifier. it may also be noted that the job of impedance matching can also be accomplished by a transformer. However the emitter follower is preferred for this purpose. it is because emitter follower is not only more convenient than a transformer but it also has much better frequency response ie.,it works well over a large frequency range.