Table of Contents

## Why zener diode as voltage regulator

Because a Zener diode is used as a **voltage stabiliser** or **voltage regulator** to provides a constant voltage from a source whose voltage may fluctuate over a wide range. The circuit diagram of a **Zener diode as a voltage stabiliser** is shown in Fig.

This is the “**circuit diagram of zener diode as voltage regulator experiment**“.

## Derivation of how to use zener diode as voltage regulator

The source voltage V_{i} and series resistance R_{s} are chosen in such a way that the diode operates in the breakdown region.

When V_{i} is less than V_{z}, then the zener diode does not conduct and current through the diode is zero. In this case, **I = I _{L}**. Therefore, current

**I**is given by

Output Voltage,

When V_{i} increases, the output voltage will increase as output voltage becomes equal to V_{Z}, the zener diode begins to conduct and voltage across it becomes constant. In this case,

Hence,

This is the minimum value of input voltage below which voltage regulation is not done by the zener regulator circuit.

When V_{i} becomes greater than the value given by egn. (2), voltage across output becomes constant and equal to V_{Z}. Therefore, the current through load resistance is given by

The excess input voltage is dropped across R_{s} so that the sum of the **voltage drop** across R_{s} and across zener diode is equal to the supply voltage V_{i}

Since

Since

The voltage V_{z} is constant and therefore the load current I_{L} is also constant. Therefore, when supply voltage V_{i} increases, the current I_{z} increases and the voltage drop across the series resistor R_{s} increases but the voltage across R_{L} is maintained constant.

The power dissipated across zener diode is given by

Thus, power dissipated across zener diode as I_{z} increases.

Maximum power dissipated is given by

Put this value in eqn. (3), we get the maximum permitted supply voltage upto which **zener diode can act as a voltage stabilizer** safely,

This is the eqn. that shows how to use zener diode as voltage regulator.

## FAQ on How to use zener diode as voltage regulator

### Why zener diode as voltage regulator?

Zener diode is used as a **voltage stabiliser** or **voltage regulator** to provides a constant voltage from a source whose voltage may fluctuate over a wide range.