What is the formula for LDO Power Dissipation (with Iq)?

The LDO Power Dissipation (with Iq) formula is Pd = (Vin − Vout) × Iout + Vin × Iq, where Pd—Total power dissipated in the LDO (W); Vin—Input voltage (V); Vout—Output voltage (V); Iout—Load current (A); Iq—Quiescent/ground current (A).

What does Pd mean in the LDO Power Dissipation (with Iq) formula?

Pd is Total power dissipated in the LDO (W).

LDO Power Dissipation (with Iq)

Q: How do you calculate LDO Power Dissipation (with Iq)?

Use the formula Pd = (Vin − Vout) × Iout + Vin × Iq. A linear regulator dissipates the voltage difference times the load current, plus the input voltage times its own quiescent (ground) current. Enter the values you know in the calculator above and it solves for the remaining variable.

Pd = (Vin − Vout)·Iout + Vin·Iq

Calculator

Power Dissipation

Input Voltage

Output Voltage

Output Current

Quiescent Current

Result

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Formula

Pd = (Vin − Vout) × Iout + Vin × Iq

Description

A linear regulator dissipates the voltage difference times the load current, plus the input voltage times its own quiescent (ground) current. The ground-current term is negligible at high load but dominates at very light load, where it sets the standby power. Including it gives a more accurate thermal estimate than the simple (Vin−Vout)·Iout figure.

Variables

Pd — Total power dissipated in the LDO (W)
Vin — Input voltage (V)
Vout — Output voltage (V)
Iout — Load current (A)
Iq — Quiescent/ground current (A)

Practical Notes

Use Pd with the junction-to-ambient thermal resistance to find die temperature. Low-Iq LDOs matter for always-on and battery standby rails where Iout is tiny.

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