Zener Regulator Calculator Formula

Understand the math behind the zener regulator calculator. Each variable explained with a worked example.

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Formulas Used

Series Resistor

series_resistor = (input_voltage - zener_voltage) / total_current_a

Resistor Power

resistor_power_mw = (input_voltage - zener_voltage) * total_current_a * 1000

Zener Power

zener_power_mw = zener_voltage * total_current_a * 1000

Variables

VariableDescriptionDefault
input_voltageInput Voltage(V)12
zener_voltageZener Voltage(V)5.1
load_current_maLoad Current(mA)20
zener_min_current_maZener Minimum Current(mA)5
total_current_aDerived value= (load_current_ma + zener_min_current_ma) / 1000calculated

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.

input_voltage = 12zener_voltage = 5.1load_current_ma = 20zener_min_current_ma = 5
  1. 01Total current = (20 + 5) / 1000 = 0.025 A
  2. 02R = (12 - 5.1) / 0.025 = 276 ohms
  3. 03Resistor power = 6.9 x 0.025 x 1000 = 172.5 mW
  4. 04Zener power = 5.1 x 0.025 x 1000 = 127.5 mW

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