Zener Regulation Resistor
R = (Vin − Vz) / (Iz + Iload)
Quick answer
This calculator solves R = (Vin - Vz) / (Iz + Iload) for Resistance. With Input Voltage 120 V, Zener Voltage 56.4 V, Zener Current 0.2 A, Load Current 94 mA, the result is 0.2163 kΩ. It solves in 5 directions, so you can enter the values you have and get the one you need.
Calculator
Formula
Description
A Zener diode regulator uses a series resistor to drop the excess voltage between the input supply and the Zener voltage. The resistor must carry both the Zener current (needed to keep the diode in its breakdown region) and the load current. The Zener current should be at least 5-10mA for stable regulation. When the load current increases, the Zener current decreases by the same amount, maintaining a roughly constant voltage. This simple regulator is suitable only for low-current, low-precision applications due to its poor efficiency and load regulation.
Variables
- R — Series resistor value (Ω)
- Vin — Input supply voltage (V)
- Vz — Zener breakdown voltage (V)
- Iz — Minimum Zener current for regulation (A)
- Iload — Maximum expected load current (A)
Practical Notes
Check that the resistor power rating exceeds (Vin - Vz)² / R, and that the Zener power rating exceeds Vz × (Iz + Iload). For better regulation, use a Zener-fed transistor regulator or an IC voltage regulator. Zener voltage has a temperature coefficient that can be positive or negative depending on the voltage rating.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| R | Resistance | Ω | mΩ, Ω, kΩ, MΩ |
| Vin | Input Voltage | V | pV, nV, µV, mV, V, kV |
| Vz | Zener Voltage | V | pV, nV, µV, mV, V, kV |
| Iz | Zener Current | mA | pA, nA, µA, mA, A, kA |
| Iload | Load Current | mA | pA, nA, µA, mA, A, kA |
Step by step
- 1. What you know: Input Voltage 120 V, Zener Voltage 56.4 V, Zener Current 0.2 A, Load Current 94 mA
- 2. The relation: R = (Vin - Vz) / (Iz + Iload)
- 3. Substitute: Vin = 120 V, Vz = 56.4 V, Iz = 0.2 A, Iload = 94 mA
- 4. Result: Resistance = 0.2163 kΩ
Related quantities from the same inputs
- P = V × I = 24 W
Nearest standard component values
| Series | Nearest value | Error |
|---|---|---|
| E12 | 0.22 kΩ | 1.7% |
| E24 | 0.22 kΩ | 1.7% |
Worked examples
Minimum range
Given: Input Voltage 3.3 V, Zener Voltage 1.55 V, Zener Current 1 mA, Load Current 0.47 mA
Result: Resistance = 1.19 kΩ
Low range
Given: Input Voltage 33 V, Zener Voltage 15.5 V, Zener Current 10 mA, Load Current 4.7 mA
Result: Resistance = 1.19 kΩ
Typical
Given: Input Voltage 120 V, Zener Voltage 56.4 V, Zener Current 0.2 A, Load Current 94 mA
Result: Resistance = 0.2163 kΩ
High range
Given: Input Voltage 2.3 kV, Zener Voltage 1.08 kV, Zener Current 5 A, Load Current 2.35 A
Result: Resistance = 0.166 kΩ
Maximum range
Given: Input Voltage 23 kV, Zener Voltage 10.8 kV, Zener Current 50 A, Load Current 23.5 A
Result: Resistance = 0.166 kΩ
Solving for each variable
Solve for Resistance
Input Voltage 3.3 V, Zener Voltage 1.55 V, Zener Current 1 mA, Load Current 0.47 mA → 1.19 kΩ
Solve for Input Voltage
Resistance 1 Ω, Zener Voltage 0.726 V, Zener Current 100 µA, Load Current 0.22 mA → 0.7263 V
Solve for Zener Voltage
Resistance 1 Ω, Input Voltage 0.33 V, Zener Current 100 µA, Load Current 0.22 mA → 0.3297 V
Solve for Zener Current
Resistance 1 Ω, Input Voltage 0.33 V, Zener Voltage 0.726 V, Load Current 0.22 mA → -0.3962 A
Solve for Load Current
Resistance 1 Ω, Input Voltage 0.33 V, Zener Voltage 0.726 V, Zener Current 100 µA → -0.3961 A
How Resistance changes with Input Voltage
| Input Voltage (input) | Resistance (result) |
|---|---|
| 0.48 kV | 0.3375 kΩ |
| 0.84 kV | 0.9 kΩ |
| 1.2 kV | 1.463 kΩ |
The same result in other units
| Unit | Value |
|---|---|
| mΩ | 216300 |
| Ω | 216.3 |
| kΩ | 0.2163 |
| MΩ | 0.0002163 |
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<p><a href="https://vbatpower.com/formulas/zener-resistor/">Zener Regulation Resistor</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Zener Regulation Resistor?
Use R = (Vin - Vz) / (Iz + Iload). With Input Voltage 120 V, Zener Voltage 56.4 V, Zener Current 0.2 A, Load Current 94 mA, Resistance works out to 0.2163 kΩ.
What is the formula for Zener Regulation Resistor?
The formula is R = (Vin - Vz) / (Iz + Iload). A Zener diode regulator uses a series resistor to drop the excess voltage between the input supply and the Zener voltage.
How do you find Input Voltage when you know the other values?
Rearrange for Input Voltage: with Resistance 1 Ω, Zener Voltage 0.726 V, Zener Current 100 µA, Load Current 0.22 mA, Input Voltage is 0.7263 V.
How do you find Zener Voltage when you know the other values?
Rearrange for Zener Voltage: with Resistance 1 Ω, Input Voltage 0.33 V, Zener Current 100 µA, Load Current 0.22 mA, Zener Voltage is 0.3297 V.
What units does Zener Regulation Resistor use?
Resistance is shown in mΩ, Ω, kΩ, MΩ. Values are held in SI base units internally, so you can mix prefixes without converting by hand.
Related Concepts
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