The zener diode can act as a voltage regulator and hold a parallel voltage constant while there may be variations in the load current.  Zener diodes are semiconductor diodes which have been manufactured to have their reverse breakdown occur at a specific, well-defined voltage (its “Zener voltage”), and that are designed such that they can be operated continuously in that breakdown mode.

This equation calculates three separate values for the Zener Voltage Regulator.  The User can choose to output the Resistance in ohms, the resistor size in watts, or the Zener diode size in Watts.

Notes

Zener Diode as Voltage Regulators

The function of a regulator is to provide a constant output voltage to a load connected in parallel with it in spite of the ripples in the supply voltage or the variation in the load current and the zener diode will continue to regulate the voltage until the diodes current falls below the minimum IZ(min) value in the reverse breakdown region.

A zener diode of break down voltage Vz is reverse connected to an input voltage source Vi across a load resistance RL and a series resistor RS. The voltage across the zener will remain steady at its break down voltage VZ for all the values of zener current IZ as long as the current remains in the break down region. Hence a regulated DC output voltage V0 = VZ is obtained across RL, whenever the input voltage remains within a minimum and maximum voltage.