Zener Diode Resistor Calculator

A Zener diode shunt regulator requires a series resistor to limit current. This tool calculates resistor value and power ratings for no-load and loaded circuits.

Formulas

R = (Vs − Vz) / (Iz + IL)

P_R = (Vs − Vz) × (Iz + IL)

P_Z = Vz × Iz

Common Zener Diodes

Part No.	Vz	Rating
1N4728A	3.3 V	1 W
1N4733A	5.1 V	1 W
1N4739A	9.1 V	1 W
1N4742A	12 V	1 W
BZX55C5V1	5.1 V	0.5 W

Design Tips

Set Iz at 25–50% of the rated max current for stability.
For high-current loads, use an LDO regulator for better efficiency.
Always derate component power ratings by 2×.

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