Common Collector Amplifier and Voltage Gain

In a common collector amplifier, also known as an emitter follower, the voltage gain is less than 1. This means that the output voltage is lower than the input voltage. Let's understand why this is the case.

Working Principle of Common Collector Amplifier

The common collector amplifier is a three-terminal device that consists of a transistor, a resistor, and a load impedance. The input signal is applied to the base of the transistor, and the output is taken from the emitter terminal. The emitter is connected to the load impedance, which determines the voltage gain of the amplifier.

Voltage Gain

The voltage gain of an amplifier is defined as the ratio of the output voltage to the input voltage. It indicates how much the input voltage is amplified by the amplifier. In the case of the common collector amplifier, the voltage gain is less than 1, which means that the output voltage is lower than the input voltage.

Reasons for Less than 1 Voltage Gain

There are several reasons why the voltage gain of a common collector amplifier is less than 1:

1. Voltage Divider Effect: The load impedance connected to the emitter forms a voltage divider with the internal resistance of the transistor. This divider reduces the output voltage compared to the input voltage.

2. Voltage Drop across the Base-Emitter Junction: The base-emitter junction of the transistor has a voltage drop of around 0.6 to 0.7 volts. This voltage drop reduces the output voltage.

3. Negative Feedback: The common collector amplifier has a negative feedback mechanism due to the connection between the emitter and the load impedance. This negative feedback reduces the voltage gain.

Effects of Input Voltage and Load Impedance

The voltage gain of a common collector amplifier can vary with changes in the input voltage and load impedance. These variations are due to the nonlinear characteristics of the transistor and the load impedance.

Conclusion

In conclusion, the voltage gain of a common collector amplifier is less than 1. This is due to the voltage divider effect, voltage drop across the base-emitter junction, and negative feedback. The voltage gain can also vary with changes in the input voltage and load impedance.