This zener diode calculator sizes the series resistor for a zener voltage regulator and checks the zener power. Enter the input voltage, zener voltage, and current above.
Formulas
Series resistor Rs = (Vin − Vz) ÷ I Zener power Pz = Vz × Iz
Example
Vin = 12 V, Vz = 5.1 V, I = 20 mA: Rs = (12 − 5.1) ÷ 0.02 = 345 Ω, zener power = 5.1 × 0.02 = 0.10 W.
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Frequently Asked Questions
How do I size a zener resistor?
Subtract the zener voltage from the input voltage and divide by the current: Rs = (Vin – Vz) / I.
How much power does a zener dissipate?
Multiply the zener voltage by the current through it. Pick a diode rated above this power.
What is a zener diode used for?
It clamps a voltage to a fixed value, making a simple voltage reference or regulator.