Zener diode is a silicon semiconductor with a p-n junction diode which operates under reverse biased condition. It is used as a voltage regulator in d.c. circuit. The primary objective of the zener diode as a voltage regulator is to maintain a constant voltage. Let us say, if zener voltage of 5 V is used then, the voltage becomes constant at 5 V, and it does not change.
Zener Diode as a Voltage Regulator
There is a series resistor connected to the circuit in order to limit the current into the diode. It is connected to the positive terminal of the d.c. It works in such a way the reverse biased can also work in breakdown condition. We do not use ordinary junction diode because the low power rating diode can get damaged when we apply reverse bias above its breakdown voltage. When minimum input voltage and a maximum load current is applied, the zener diode current should always be minimum.
Since the input voltage and the required output voltage is known, it is easier to choose a zener diode with a voltage approximately equal to the load voltage, i.e. VZ = VL.
The circuit diagram of a voltage regulator using a zener diode is shown:
Current through the diode increases when the voltage across the diode tends to increase which results in voltage drop across the resistor. Similarly, current through the diode decreases when the voltage across the diode tends to decrease. Here, the voltage drop across the resistor is very less, and the output voltage results normally.
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