With the aid of a circuit diagram, describe the operation of a zener diode voltage regulator.

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A zener diode is like an ordinary diode but it is suitably doped so as to have a sharp breakdown voltage. It is always connected in a reverse biased state and it has a sharp breakdown volatage called zener volatge Vz. A zener diode is used as a voltage regulator to provide a constant voltage from the source whose voltage may vary over sufficient range.

When the circuit is properly designed, the load voltage Eo becomes equal to Vz even if the input voltage Ei and load resistance RL vary.

When the input voltage increases, the ouput voltage remains constant at Vz = Eo and the excess voltage is dropped across the series resistance R. This causes an increase in the total current I and as a result the zener will conduct the increase of current in I while the load current remains constant. Hence the output voltage Eo remains constant even if the input voltage Ei changes.

When the input voltage becomes constant and the load resistance RL decreases this causes an increase in load current hence additional load current will come from a decrease in zener current Iz.

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