Zener regulator calculator

Calculate Zener output, load and diode currents, dropout and resistor dissipation.

Schematic

Loading CircuitSim schematic…

Results

Output voltage5.1 V

Output versus supply

Output

Zener current	15.81 mA
Load current	5.1 mA
Series resistor power	144.27 mW

Advanced results

Zener dissipation	80.63 mW
Ideal minimum supply	6.78 V
Supply current	20.91 mA

How zener regulator works

R1 limits supply current. The load takes part of that current, and the reverse-biased Zener takes the remainder. If the supply cannot provide enough current to reach breakdown, the diode turns off and R1/R2 behave as an ordinary divider.

V_{out}=\min\left(V_Z,\,V_{in}\frac{R_2}{R_1+R_2}\right)

The calculation uses a constant Zener voltage. The simulated diode has a soft breakdown knee; its voltage varies with current. Check real device current and power ratings separately.

Change the form inputs or click a component value on the schematic. Choose Try in CircuitSim to simulate the configured circuit.

Do the math

Selected input values
V1	12 V
R1	330 Ω
D1	5.1 V
R2	1 kΩ

Output voltage: $V_{out}=\min\left(V_Z,\,V_{in}\frac{R_2}{R_1+R_2}\right)$
$\min\left(5.1\,\mathrm{V},9.02\,\mathrm{V}\right)$
≈ 5.1 V
Supply current: $I_S=(V_1-V_{out})/R_1$
$\frac{6.9\,\mathrm{V}}{330\,\mathrm{\Omega}}$
≈ 20.91 mA
Zener current: $I_Z=I_S-V_{out}/R_2$
$20.91\,\mathrm{mA}-\frac{5.1\,\mathrm{V}}{1\,\mathrm{k\Omega}}$
≈ 15.81 mA
Resistor dissipation: $P_{R1}=(V_1-V_{out})I_S$
$6.9\,\mathrm{V}\times 20.91\,\mathrm{mA}$
≈ 144.27 mW

Zener regulator calculator

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Schematic

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How zener regulator works

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