Zener Diode Voltage Regulator

Zener Diode Voltage Regulator- When the zener diode is operated in the breakdown or zener region, the voltage across it's mainly constant for a large change of current through it. 

This characteristic permits it to be used as a voltage regulator.

Fig-1 shows the circuit of a zener diode controller.

As long as input voltage V_in is
Lesser than zener voltage V_Z, the zener operates in the breakdown region and maintains constant voltage across the load.

The series limiting resistance R_S limits the input current Operation.

Operation

The zener will maintain constant voltage across the cargo inspite of changes in cargo
current or input voltage.

As the load current increases, the zener current diminishments so that current through resistance R_S is constant.

As affair voltage = V_in –IR_S, and I is constant, thus, affair voltage remains unchanged.

The reverse would be true should the load current drop.

The circuit will also correct for the changes in input voltages.

Should the input voltage V_in increase, more current will flow through
the zener, the voltage drop across R_S will increase but cargo voltage would remain constant.

The rear would be true should the input voltage drop.

Limitations

A zener diode controller has the following Downsides-

(i) It has low effectiveness for heavy load currents.

It's because if the load current is large, there will be considerable power loss in the series limiting resistance.

(ii) The affair voltage slightly changes due to zener impedance as V_out = V_Z+I_Z Z_Z.

Changes in load current Yield changes in zener current.

Accordingly, the affair voltage also changes.

Thus, the use of this circuit is limit to only similar operations where variations in cargo current and input voltage are small.

Conditions for Proper Operation of Zener Regulator

When a zener diode is connect in a circuit for voltage regulation, the following conditions must be satisfied :

(i) The zener must operate in the breakdown region or regulating region i.e. between I_{Z (max)} and I_{Z (min)}.

The current I_{Z (min)} (generally 10 mA) is the minimum zener current to put the zener diode in the ON state i.e. regulating region.

The current I_{Z (max)} is the maximum zener current that zener diode can conduct without getting destroy due to excessive heat.

(ii) The zener should not be allow to exceed maximum dissipation power otherwise it will be destroy due to excessive heat.

If maximum power dissipation of a zener is P_{Z (max)}and zener voltage is V_Z, then,
P_{Z (max)} = V_Z I_{Z (max)}

(iii) There is a minimum value of RL to ensure that zener diode will remain in the regulating region i.e. breakdown region.

f the value of R_L falls below this minimum value, the proper voltage will not be available across the zener to drive it into the breakdown region.