LDO Power Dissipation (with Iq)

Pd = (Vin − Vout)·Iout + Vin·Iq

Quick answer

This calculator solves Pd = (Vin − Vout) × Iout + Vin × Iq for Power Dissipation. With Input Voltage 12 V, Output Voltage 26.4 V, Output Current 20 mA, Quiescent Current 44 mA, the result is 0.24 W. It solves in 4 directions, so you can enter the values you have and get the one you need.

Calculator

Power Dissipation (W)
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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.

Symbols and units

Symbol Meaning Default unit Accepted units
Pd Power Dissipation 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
Iout Output Current mA pA, nA, µA, mA, A, kA
Iq Quiescent Current mA pA, nA, µA, mA, A, kA

Step by step

  1. 1. What you know: Input Voltage 12 V, Output Voltage 26.4 V, Output Current 20 mA, Quiescent Current 44 mA
  2. 2. The relation: Pd = (Vin − Vout) × Iout + Vin × Iq
  3. 3. Substitute: Vin = 12 V, Vout = 26.4 V, Iout = 20 mA, Iq = 44 mA
  4. 4. Result: Power Dissipation = 0.24 W

Related quantities from the same inputs

  • P = V × I = 0.24 W

Worked examples

Minimum range

Given: Input Voltage 0.33 V, Output Voltage 0.726 V, Output Current 100 µA, Quiescent Current 0.22 mA

Result: Power Dissipation = 33 µW

Low range

Given: Input Voltage 3.3 V, Output Voltage 7.26 V, Output Current 1 mA, Quiescent Current 2.2 mA

Result: Power Dissipation = 3.3 mW

Typical

Given: Input Voltage 12 V, Output Voltage 26.4 V, Output Current 20 mA, Quiescent Current 44 mA

Result: Power Dissipation = 0.24 W

High range

Given: Input Voltage 0.23 kV, Output Voltage 0.506 kV, Output Current 0.5 A, Quiescent Current 1.1 A

Result: Power Dissipation = 115 W

Maximum range

Given: Input Voltage 2.3 kV, Output Voltage 5.06 kV, Output Current 5 A, Quiescent Current 11 A

Result: Power Dissipation = 11.5 kW

Solving for each variable

Solve for Power Dissipation

Input Voltage 0.33 V, Output Voltage 0.726 V, Output Current 100 µA, Quiescent Current 0.22 mA → 33 µW

Solve for Quiescent Current

Power Dissipation 10 mW, Input Voltage 0.33 V, Output Voltage 0.726 V, Output Current 100 µA → 30.42 mA

Solve for Output Current

Power Dissipation 10 mW, Input Voltage 0.33 V, Output Voltage 0.726 V, Quiescent Current 0.22 mA → -25.07 mA

Solve for Output Voltage

Power Dissipation 10 mW, Input Voltage 0.33 V, Output Current 100 µA, Quiescent Current 0.22 mA → -98.94 V

How Power Dissipation changes with Input Voltage

Input Voltage (input) Power Dissipation (result)
9 V 48 mW
12 V 0.24 W
18 V 0.624 W
24 V 1.008 W
48 V 2.544 W
84 V 4.848 W
120 V 7.152 W

The same result in other units

Unit Value
µW 240000
mW 240
W 0.24
kW 0.00024

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Frequently asked questions

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

Use Pd = (Vin − Vout) × Iout + Vin × Iq. With Input Voltage 12 V, Output Voltage 26.4 V, Output Current 20 mA, Quiescent Current 44 mA, Power Dissipation works out to 0.24 W.

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

The formula is 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.

How do you find Quiescent Current when you know the other values?

Rearrange for Quiescent Current: with Power Dissipation 10 mW, Input Voltage 0.33 V, Output Voltage 0.726 V, Output Current 100 µA, Quiescent Current is 30.42 mA.

How do you find Output Current when you know the other values?

Rearrange for Output Current: with Power Dissipation 10 mW, Input Voltage 0.33 V, Output Voltage 0.726 V, Quiescent Current 0.22 mA, Output Current is -25.07 mA.

What units does LDO Power Dissipation (with Iq) use?

Power Dissipation is shown in µW, mW, W, kW. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

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