Linear Regulator Dissipation
P = (Vin − Vout) × I
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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.
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