A zener diode voltage regulator uses the diode's reverse breakdown characteristic to clamp a voltage at a fixed level. The series resistor sets the current through the zener, and both components dissipate power as heat. This calculator finds the correct resistor value and power ratings.
Circuit Parameters
Common values: 2.4V, 3.3V, 5.1V, 6.2V, 9.1V, 12V
Typical: 5–20 mA. Must exceed Iz_min from datasheet.
Enter circuit values and click Calculate
How to Use the Zener Diode Calculator
This zener diode calculator designs a simple shunt voltage regulator circuit. Enter your supply voltage, desired output voltage (zener voltage), zener operating current, and load current to find the series resistor value and power ratings.
Design Formula
The series resistor: Rs = (Vs − Vz) / (Iz + IL). At maximum load removal (IL = 0), all current flows through the zener: Iz_max = (Vs − Vz) / Rs. Choose the zener's power rating to exceed Vz × Iz_max with a 2× safety margin. Choose the resistor's power rating to exceed (Vs − Vz)² / Rs with a 2× safety margin.
Choosing Zener Diodes
Common zener voltages: 2.4V, 3.3V, 4.3V, 5.1V, 5.6V, 6.2V, 6.8V, 7.5V, 8.2V, 9.1V, 10V, 12V, 15V. Power ratings: 0.5W (small signal), 1W, 2W, 5W. Always operate the zener above its minimum current (Iz_min, typically 5mA) to maintain regulation. Always stay below its maximum current rating.
FAQ
Is this zener diode calculator free?
Yes, completely free. Calculate series resistor and power dissipation without any account or payment.
Is my data private?
All calculations run in your browser. No data is sent to any server.
What is a zener diode?
A zener diode is a special diode designed to operate in reverse breakdown mode. Unlike regular diodes, it maintains a nearly constant voltage (the zener voltage) across its terminals when reverse voltage exceeds its rated value. This makes it ideal for voltage regulation.
How do I calculate the series resistor for a zener circuit?
The series resistor formula is Rs = (Vs - Vz) / (Iz + IL), where Vs is supply voltage, Vz is zener voltage, Iz is the desired zener current (5-20mA typical), and IL is load current. The resistor must dissipate P = (Vs - Vz)² / Rs watts.
What wattage zener diode do I need?
Zener power dissipation is Pz = Vz × Iz_max, where Iz_max occurs when the load is disconnected and all current flows through the zener. Choose a zener with a power rating at least 2× the calculated dissipation (e.g., 1W zener for 500mW dissipation).
What is the minimum zener current?
Zener diodes need a minimum current (typically 5mA) to maintain regulation. Below this, the voltage becomes unstable. The circuit must ensure at least minimum current flows through the zener even at maximum load.
When should I use a zener regulator vs a linear regulator IC?
Use a zener regulator for simple low-current references (under 50mA) and when you need minimal components. Use a linear IC (LM317, 7805) for higher current loads, better regulation accuracy, and when efficiency matters more. Zener regulators waste power in the resistor.