Emitter Follower Circuit | Operation | Characteristics | New Topic [2023]

In this note, We are discussing the Emitter Follower Circuit and also discussing about operation of Emitter Follower and Characteristics. Welcome to Poly Notes Hub, a leading destination for polytechnic notes.

Author Name: Arun Paul.

Introduction of Emitter Follower Circuit

It is a negative current feedback circuit. The emitter follower is a current amplifier that has no voltage gain. Its most important characteristics it that it has high input impedance and low output impedance. This makes it an ideal circuit for impedance matching.

Circuit Details

Circuit details Fig shows the circuit of an emitter follower. As you can see, it differs from the circuitry of a conventional CE amplifier in the absence of a collector load and emitter bypass capacitor. The emitter resistance RE itself acts as the load and AC output voltage (Vout) is taken across RE. The biasing is generally provided by the voltage-divider or the base resistor methods.

The following points are worth noting about the emitter follower:

1. There is neither a collector resistor in the circuit nor an emitter capacitor. These are the two circuit recognition features of this circuit.
2. Since the collector is at AC ground, this circuit is known as a common collector (CC) amplifier.

Operation of Emitter Follower

The input voltage is applied between the base and emitter and the resulting AC emitter current produces an output voltage i.e. RE across the emitter resistance. This voltage opposes the input voltage, thus providing negative feedback. It is a negative current feedback circuit since the voltage feedback is proportional to the emitter current i.e., the output current. It is called an emitter follower because the output voltage follows the input voltage.

Characteristics

The major characteristics of this circuit are:

1. No voltage gain. In fact, the voltage gain of this circuit is close to 1.
2. Relatively high current gain and power gain.
3. High input impedance and low output impedance.
4. Input and output ac voltage are in phase.

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