What is voltage regulation? Explain the working of Zener diode as a voltage regulator.

Answer:

Voltage regulation: Keeping the output (load) voltage of a power supply constant in spite of changes in the input voltage or in the load current is called voltage regulation.

[Figure: unregulated d.c. input \(V_{in}\) connected through a series resistance \(R_S\) to a Zener diode which is reverse biased (cathode to the positive side). The load resistance \(R_L\) is connected in parallel with the Zener diode; the output \(V_0 = V_Z\) is taken across \(R_L\). Currents: \(I\) through \(R_S\), \(I_Z\) through the Zener, \(I_L\) through the load, with \(I = I_Z + I_L\).]

Working: The Zener diode is chosen with breakdown voltage \(V_Z\) equal to the required output, and \(V_{in} \gt V_Z\). In the breakdown region the voltage across the Zener remains practically constant at \(V_Z\) for a wide range of current. \(V_{in} = IR_S + V_Z\).

• If the input voltage increases, the current \(I\) through \(R_S\) increases. The extra current flows through the Zener (\(I_Z\) increases), so the extra voltage drops across \(R_S\) and the output stays at \(V_Z\).
• If the input voltage decreases, \(I\) and \(I_Z\) decrease, the drop across \(R_S\) decreases, and the output again stays at \(V_Z\).
• If the load current changes, \(I_Z\) adjusts in the opposite way so that \(I\) and the drop across \(R_S\) remain nearly constant.

Thus the output voltage remains constant at \(V_Z\) and the Zener diode works as a voltage regulator.