Zener diode as voltage regulator circuit diagram

A Zener diode is a special type of diode, designed to operate in the reverse breakdown region, which is beyond its normal reverse bias breakdown voltage. Zener diodes are primarily used as voltage regulators, specifically in applications where a stable and precise voltage output is required despite variations in the input voltage or load conditions. Let us analyze circuit diagram of zener diode as voltage regulator.

Once the diode has breakdown mode, very little change in voltage across zener diode will result into change in current through the diode. Hence zener diode having known breakdown voltage can be used as reference voltage in reverse biased mode. It is used to regulate the voltages.

Voltage regulation is a measure of ability of circuit to maintain constant voltage output under variation either in input voltage or load current.

Figure depicts voltage regulator circuit and zener diode equivalent circuit. As shown, resistor Rs is used to limit reverse current through the diode to safe value. Both Vs and Rs are selected such that diode operates in breakdown region.

The series resistor Rs absorbs output voltage fluctuations to maintain voltage across load to constant value.
Is = (Vs-Vz)/Rs
Where in Is = Iz + I_L

Zener diode maintains constant voltage across load as long as supply voltage is more than zener voltage.

Merits and demerits of zener diode as voltage regulator

It is preferred over other voltage regulator types, as they are lighter, smaller and have long life. Moreover they are cheaper and simple to develop.

Following are the demerits of zener diode voltage regulator :
• Efficiency is low for high load currents.
• Output voltage slightly varies due to zener impedance(rz).
• Output voltage depends on breakdown voltage of zener diode and can not be selected as separate voltage.

In summary, a Zener diode is designed to operate in the reverse breakdown region. It maintains stable voltage drop across its terminals when operated in this region. This controlled breakdown behavior of Zener diodes make it useful for voltage regulation and protection of various electronic circuits.

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