Zener Diode Resistor Calculator
Enter the supply voltage, Zener voltage and the load current.
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Zener Diode Resistor Calculator by TheCalcTools
How the Zener Diode Resistor Calculator works
The resistor drops the difference between the supply and the Zener voltage while passing the load current plus a minimum Zener current to keep it regulating: R = (Vin − Vz) ÷ (IL + Iz).
If the load is disconnected, all the current flows through the Zener, so pick a Zener rated well above that worst-case power. Choose the next standard resistor value below the result.
The formula
Worked example
Using the default values shown in the calculator:
| Supply voltage (V) | 12 |
|---|---|
| Zener voltage (V) | 5.1 |
| Load current (mA) | 20 |
| Minimum Zener current (mA) | 5 |
- 12 V to 5.1 V for 20 mA plus 5 mA: R = 276.0 Ω.
- The resistor dissipates 0.173 W; the Zener up to 0.128 W with no load.
Result:
| Series resistor (Ω) | 276.0 |
|---|---|
| Resistor power (W) | 0.173 |
| Zener power with no load (W) | 0.128 |
| Total current (mA) | 25.0 |
Frequently asked questions
Is a Zener a good regulator?
For small, steady loads. For more current or efficiency use a linear or switching regulator.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.