Zener Diode Regulator Calculator: Series Resistor, Zener Current and Power, and Minimum Supply
Check a simple Zener shunt regulator.
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How this calculator works
Enter the supply, the Zener voltage and the series resistor.
Enter the load resistance and the Zener power rating.
The calculator gives the currents, the power and the checks.
Formulas used
- I_S = \frac{V_{in} - V_Z}{R_S}
- I_Z = I_S - I_L
- P_Z = V_ZI_Z
Worked example
With the default numbers in the calculator above:
- Current through the series resistor: 31.3636 mA
- Load current: 5.1 mA
- Current through the Zener diode: 26.2636 mA
- Power in the Zener diode: 133.945 mW
- Power in the series resistor: 0.216409 W
- Smallest supply voltage that keeps the output regulated: 6.222 V
Change the numbers in the calculator to see the full working, every step, for your own case.
Common questions
How do I choose the series resistor?
It must pass enough current for the load plus a minimum Zener current at the lowest supply voltage, and not so much that the Zener overheats at the highest supply and lightest load.
Why check the no-load case?
With the load removed, all the current goes through the Zener, so that is where it dissipates the most power.
Is a Zener regulator efficient?
No. The resistor and the diode waste power all the time, so it suits small loads. For more power use a linear or switching regulator.
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Got a question about this? Ask an engineering question and get a plain-language answer with references.
Further reading: Any electronics text (Zener diode voltage regulators).
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