Zener Regulator Calculator Formula
Understand the math behind the zener regulator calculator. Each variable explained with a worked example.
Formulas Used
Series Resistor
series_resistor = (input_voltage - zener_voltage) / total_current_aResistor Power
resistor_power_mw = (input_voltage - zener_voltage) * total_current_a * 1000Zener Power
zener_power_mw = zener_voltage * total_current_a * 1000Variables
| Variable | Description | Default |
|---|---|---|
input_voltage | Input Voltage(V) | 12 |
zener_voltage | Zener Voltage(V) | 5.1 |
load_current_ma | Load Current(mA) | 20 |
zener_min_current_ma | Zener Minimum Current(mA) | 5 |
total_current_a | Derived value= (load_current_ma + zener_min_current_ma) / 1000 | calculated |
How It Works
Zener Diode Voltage Regulator
A zener diode in reverse breakdown maintains a nearly constant voltage.
Formula
R_series = (V_in - V_zener) / (I_load + I_zener_min)
The resistor drops excess voltage. The zener must carry at least its minimum current for proper regulation even at full load.
Worked Example
Regulate 12 V down to 5.1 V for a 20 mA load. Zener needs 5 mA minimum.
- 01Total current = (20 + 5) / 1000 = 0.025 A
- 02R = (12 - 5.1) / 0.025 = 276 ohms
- 03Resistor power = 6.9 x 0.025 x 1000 = 172.5 mW
- 04Zener power = 5.1 x 0.025 x 1000 = 127.5 mW
Frequently Asked Questions
When should I use a zener regulator?
For low-current loads under 100 mA where simplicity matters more than efficiency. For higher currents use a linear or switching regulator.
Why does the zener need minimum current?
Below its minimum reverse current the zener does not maintain a stable breakdown voltage and regulation fails.
How do I choose the zener wattage?
Use at least 2x the calculated zener power for safety margin. Common ratings are 250 mW, 500 mW, and 1 W.
Ready to run the numbers?
Open Zener Regulator Calculator