Write briefly, how a Zener diode acts as voltage regulator.

Explanation

For the proper functioning of Zener diode, it must be reverse biased. Zener diode as a voltage regulator:
A zener diode can be used as voltage regulator or voltage stabilizer to provide a constant voltage. The circuit diagram showing Zener diode as voltage stabilizer is shown in the Figure. The Zener diode is connected across the fluctuating voltage (input) through a resistance R. When the input voltage increases, resistance of the Zener diode decreases and current through diode increases. As a result the voltage drop occurs across R. Hence, the output voltage is maintained to the desired value. When the input voltage decreases, current through diodes also decreases. So small voltage drop occurs across R and the desired output is maintained.