Linear Regulator Dissipation
P = (Vin − Vout) × I
Quick answer
This calculator solves P = (Vin - Vout) × Iload for Power. With Input Voltage 120 V, Output Voltage 56.4 V, Load Current 20 A, the result is 1.272 kW. It solves in 4 directions, so you can enter the values you have and get the one you need.
Calculator
Formula
Description
Linear voltage regulators work by dropping the excess voltage between input and output as heat. The power dissipated is simply the voltage difference multiplied by the load current. This heat must be managed through proper heatsinking or the regulator will enter thermal shutdown or suffer permanent damage. Linear regulators are simple and produce clean output with low noise, but their efficiency drops as the input-output voltage differential increases. For example, regulating 12V down to 3.3V at 500mA wastes 4.35W as heat while delivering only 1.65W to the load.
Variables
- P — Power dissipated as heat (W)
- Vin — Input voltage (V)
- Vout — Regulated output voltage (V)
- Iload — Load current (A)
Practical Notes
Always check that the regulator's maximum junction temperature is not exceeded. The dropout voltage is the minimum Vin-Vout differential for proper regulation, typically 1-2V for standard regulators and 0.1-0.5V for LDOs (Low Dropout Regulators). When efficiency matters and the voltage differential is large, consider a switching regulator instead.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| P | Power | W | µW, mW, W, kW |
| Vin | Input Voltage | V | pV, nV, µV, mV, V, kV |
| Vout | Output Voltage | V | pV, nV, µV, mV, V, kV |
| I | Load Current | A | pA, nA, µA, mA, A, kA |
Step by step
- 1. What you know: Input Voltage 120 V, Output Voltage 56.4 V, Load Current 20 A
- 2. The relation: P = (Vin - Vout) × Iload
- 3. Substitute: Vin = 120 V, Vout = 56.4 V, I = 20 A
- 4. Result: Power = 1.272 kW
Related quantities from the same inputs
- P = V × I = 2.4 kW
Worked examples
Minimum range
Given: Input Voltage 3.3 V, Output Voltage 1.55 V, Load Current 20 mA
Result: Power = 35 mW
Low range
Given: Input Voltage 33 V, Output Voltage 15.5 V, Load Current 0.2 A
Result: Power = 3.5 W
Typical
Given: Input Voltage 120 V, Output Voltage 56.4 V, Load Current 20 A
Result: Power = 1.272 kW
High range
Given: Input Voltage 2.3 kV, Output Voltage 1.08 kV, Load Current 1 kA
Result: Power = 1220 kW
Maximum range
Given: Input Voltage 23 kV, Output Voltage 10.8 kV, Load Current 10 kA
Result: Power = 122000 kW
Solving for each variable
Solve for Power
Input Voltage 3.3 V, Output Voltage 1.55 V, Load Current 20 mA → 35 mW
Solve for Input Voltage
Power 10 mW, Output Voltage 0.726 V, Load Current 2 mA → 5.726 V
Solve for Output Voltage
Power 10 mW, Input Voltage 0.33 V, Load Current 2 mA → -4.67 V
Solve for Load Current
Power 10 mW, Input Voltage 0.33 V, Output Voltage 0.726 V → -25.25 mA
How Power changes with Input Voltage
| Input Voltage (input) | Power (result) |
|---|---|
| 0.48 kV | 4.32 kW |
| 0.84 kV | 11.52 kW |
| 1.2 kV | 18.72 kW |
The same result in other units
| Unit | Value |
|---|---|
| mW | 1272000 |
| W | 1272 |
| kW | 1.272 |
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<p><a href="https://vbatpower.com/formulas/regulator-dissipation/">Linear Regulator Dissipation</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Linear Regulator Dissipation?
Use P = (Vin - Vout) × Iload. With Input Voltage 120 V, Output Voltage 56.4 V, Load Current 20 A, Power works out to 1.272 kW.
What is the formula for Linear Regulator Dissipation?
The formula is P = (Vin - Vout) × Iload. Linear voltage regulators work by dropping the excess voltage between input and output as heat.
How do you find Input Voltage when you know the other values?
Rearrange for Input Voltage: with Power 10 mW, Output Voltage 0.726 V, Load Current 2 mA, Input Voltage is 5.726 V.
How do you find Output Voltage when you know the other values?
Rearrange for Output Voltage: with Power 10 mW, Input Voltage 0.33 V, Load Current 2 mA, Output Voltage is -4.67 V.
What units does Linear Regulator Dissipation use?
Power is shown in mW, W, kW. Values are held in SI base units internally, so you can mix prefixes without converting by hand.
Related Concepts
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