What is the need for Dual Power Supply in Differential Amplifier? Compare working with Single & Dual Power Supply

The differential amplifier works good, on dual power supply only. However, if it is connected with single power supply, then it’s working becomes unstable. So its comparative points of its working for dual and single power supply are given below.

Important Links: Watch this video to learn detailed working of differential amplifier. Also read the four types of modes of differential amplifier.

Using Single Power Supply

Suppose single power supply is used for circuit, i.e. ground terminal is common to all the circuit.

The resistors R₁, R₂, R₃ and R₄ form potential dividers. Now the base of each transistor is at +6V.

So each transistor goes in saturation region. When input signal is connected, the transistors cannot amplify the signals because they are already in saturation and so effective amplification is not possible.

Thus, overall working is not stable, due to single supply.

Using Dual Power Supply                                                 

Suppose dual power supply is used, i.e. ground terminal is common ground to input signals only.

The resistors R₁, R₂, R₃ and R₄ form potential dividers. Their values of R₂ and R₄ are so selected to keep base voltage at 0.6V, i.e. each transistor remains in active region. Practically this can be done by keeping the values of R₂ and R₄ slightly greater than R₁ and R₃. So it can amplify input signals effectively.

So distortion at the output becomes zero and overall working is stable with dual power supply.