Zener Regulator

The constant reverse voltage of the zener diode makes it a valuable component for the regulation of the output voltage against both variations in the input voltage from an unregulated power supply or variations in the load resistance. The current through the zener will change to keep the voltage at within the limits of the threshold of zener action and the maximum power it can dissipate.

Zener Regulator Design

One strategy for designing a Zener regulator circuit is to design for a maximum power dissipated in the zener diode when the regulator is open circuited.

For a zener voltage

= V and a maximum power of P = W,

the resistor

must limit the current to

= mA .

If the input voltage is

= volts,

then you will require a resistor

=

to protect the zener in open circuit.

This design with a load resistance

=

will give an output current

=

mA

and output power

= W

To do this, it will require input power

= W.

The logic of this design strategy is to protect the zener diode. The designed resistor limits the current so that you don't burn out the zener diode if the load resistor gets disconnected.

Calculation note: You may substitute values for the zener voltage, the maximum power, the input voltage, or the load resistor. The other parameters will be calculated. Default values will be entered for unspecified parameters used in the calculation.

If you experiment with the input values, you will discover some of the practical truths about zener-regulated power supplies. If you start with an unregulated power supply which is closer to, but not less than, the zener voltage, you will be able to get more regulated power out without open-circuit risk to the zener diode. The circuit will also be more efficient in power use.