Zener Diode Resistor Calculator

This calculator works out the series resistor you need to build a simple Zener diode voltage regulator or reference circuit, along with the power each component must dissipate. A Zener diode holds a steady voltage across itself once enough current flows through it in reverse, but it relies on a series resistor to drop the remaining voltage and limit that current to a safe level; get the resistor wrong and you either starve the Zener of current or exceed its power rating. Enter your input voltage (Vin), the Zener's rated voltage (Vz), and the current you want flowing through the Zener (Iz), and the calculator returns the series resistor value in ohms using R = (Vin - Vz) / Iz, plus the power dissipated in the Zener (Vz x Iz) and in the resistor ((Vin - Vz) x Iz). Compare both figures against the actual wattage ratings of the parts you use, and choose components rated comfortably above the calculated dissipation. Remember this is a no-load calculation; if the regulated output also feeds a load, the resistor must supply the load current on top of Iz, so size it for the worst case. The results assume ideal components and are rounded for display, so treat them as a solid starting point for prototyping rather than a substitute for checking real datasheet tolerances.

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