Linear Regulator Power Dissipation Calculator
Enter the input and output voltages, the load current and the thermal resistance.
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Linear Regulator Power Dissipation Calculator by TheCalcTools
How the Linear Regulator Power Dissipation Calculator works
A linear regulator burns off the voltage difference as heat: P = (Vin − Vout) × I, plus a little for its own quiescent current. Efficiency is roughly Vout ÷ Vin.
Junction temperature = ambient + power × thermal resistance. Most regulators shut down or fail around 125 to 150 °C, so keep a margin.
The formula
Worked example
Using the default values shown in the calculator:
| Input voltage (V) | 12 |
|---|---|
| Output voltage (V) | 5 |
| Load current (A) | 0.5 |
| Quiescent current (mA) | 5 |
| Thermal resistance junction to air (°C/W) | 50 |
| Ambient temperature (°C) | 25 |
- 12 V to 5 V at 0.5 A: 3.560 W of heat, efficiency 41.3%.
- At 50 °C/W the junction reaches 203.0 °C: Too hot: add a heatsink, lower the input voltage or use a switching regulator.
Result:
| Power dissipated (W) | 3.560 |
|---|---|
| Efficiency | 41.3% |
| Junction temperature (°C) | 203.0 |
| Thermal check | Too hot: add a heatsink, lower the input voltage or use a switching regulator |
Frequently asked questions
Why does my 7805 get so hot?
Dropping 12 V to 5 V at 0.5 A wastes 3.5 W; without a heatsink that is far too much for a TO-220 package.
Sources and further reading
- Wikipedia: Linear regulator
- Texas Instruments: Understanding thermal dissipation and design of a heatsink (SLVA462)
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.