Zener Diode Regulator Calculator

About this tool

Size the series resistor for a basic zener diode shunt voltage regulator from the input voltage, zener voltage, target zener current, and optional load current — plus the power each part needs to dissipate, so you can pick resistor and zener wattage ratings that won't overheat.

Frequently asked questions

What's the formula for the series resistor?

R = (Vin − Vz) / (Iz + IL) — the resistor must drop the difference between input and zener voltage while carrying both the zener's own current and whatever the load draws.

Why include load current if it's optional?

With no load, all the resistor's current flows through the zener, which is the worst case for zener power dissipation. Adding expected load current gives a more realistic (usually lower) zener current and a resistor sized for real operating conditions.

Is a zener shunt regulator efficient?

Not particularly — the series resistor and zener continuously dissipate power even when the load draws little current, which is why zener regulators are mainly used for low-power reference/bias circuits rather than as a main power supply.