Zener Diode Calculator

What is a Zener Diode?

A Zener diode is a special type of diode designed to conduct in reverse bias once the voltage reaches the Zener breakdown voltage (Vz). This makes it ideal for voltage regulation — holding the output at a constant voltage even as the input and load current vary.

The Basic Zener Regulator Formula

R_series = (V_in − V_z) / I_z

Where I_z is the total Zener current, which must be enough to keep the Zener in regulation even at maximum load current.

To calculate the Zener current at a given operating point: I_z = (V_in − V_z) / R_series − I_load

How to Use This Calculator

Enter the input voltage, Zener voltage, series resistor value, and load current. The calculator returns Zener current, power dissipated in the Zener and resistor, and whether the circuit is in regulation.

Practical Examples

Example 1: 12V input, 5.1V Zener, 470Ω series resistor, 10mA load. I_total = (12 − 5.1) / 470 = 14.7mA. I_z = 14.7 − 10 = 4.7mA. ✓ In regulation. Zener power = 5.1 × 0.0047 = 24mW.

Example 2: 9V input, 6.8V Zener (1W), 100Ω series resistor. I_total = (9 − 6.8) / 100 = 22mA. Zener power = 6.8 × 0.022 = 150mW. Well within 1W rating.

Limitations

Zener regulators are simple but inefficient — excess voltage is wasted as heat. For higher currents or better regulation, use a linear regulator IC (LM7805, LDO) or switching regulator.