Linear Regulator Power Dissipation Calculator
A linear voltage regulator works by burning off the excess voltage between its input and output as heat in a pass transistor. The wasted power equals the voltage it drops times the load current, plus a small amount from its own quiescent current. This determines how hot the part runs and whether a heatsink is needed. This calculator takes the input and output voltages, the load current, and the quiescent current, then returns the power dissipated, the useful output power, the total input power, and the conversion efficiency.
Regulator dissipation formula
Dissipation P = (Vin - Vout) * Iload + Vin * Iq
Output power = Vout * Iload
Input power = Vin * (Iload + Iq)
Efficiency = 100 * Output power / Input power
By conservation of energy, input power equals output power plus dissipated power. The pass element drops the voltage difference at the load current, and the regulator's quiescent current adds a small extra draw from the input.
Linear regulator facts
- Linear regulator efficiency is roughly Vout divided by Vin.
- All dropped voltage becomes heat in the pass transistor.
- Low-dropout (LDO) parts work with small Vin minus Vout headroom.
- Large voltage drops at high current call for a switching regulator instead.
- Junction temperature rise equals dissipation times thermal resistance.
Linear regulator dissipation: frequently asked questions
How much power does a linear regulator dissipate?
A linear regulator drops the difference between input and output voltage across the pass element while carrying the load current. The dissipation is (Vin - Vout) times the load current, plus a small term for the regulator's own quiescent current times the input voltage. All of this becomes heat.
Why are linear regulators inefficient at large voltage drops?
A linear regulator passes essentially the same current to the load as it draws from the input, so its efficiency is roughly Vout divided by Vin. Dropping 12 volts to 3.3 volts at 1 amp wastes about 8.7 watts as heat and is only about 28 percent efficient. Large drops favour a switching regulator.
What is quiescent current and does it matter?
Quiescent current is the current the regulator itself consumes to operate, separate from the load. It adds a small dissipation term Vin times Iq. For most power-delivery use it is tiny, but in low-power and battery applications it can dominate, so this calculator includes it as an editable input.
How do I know if the regulator will overheat?
Compare the dissipation to the regulator's thermal limit. The junction temperature rise equals dissipation times the junction-to-ambient thermal resistance. If the resulting junction temperature exceeds the rated maximum, you need a heatsink, lower input voltage, or a switching design.
Is efficiency the same as one minus the loss fraction?
Efficiency here is output power divided by input power: Vout times load current divided by (Vin times (load current plus quiescent current)). One minus this fraction is the proportion of input power lost as heat in the regulator.
Official sources
- NIST: Physical Measurement Laboratory: electrical power units.
- IEEE: IEEE standards for power electronics terminology.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.