MOSFET Power Loss Calculator

Calculate MOSFET conduction loss, switching loss, gate drive loss, total heat and junction temperature for PWM drivers, buck converters, motor drivers and power switching circuits.

⚡ Maker Rule: MOSFET heat is usually a mix of I²R conduction loss and switching loss. Low Rds(on) helps conduction, but slow switching can still make the MOSFET hot. Use this with the MOSFET Gate Resistor Calculator, Regulator Heat Sink Calculator, Buck Inductor Calculator and PCB Trace Width Calculator.

🔥 MOSFET Loss Path — Current + Switching + Heat

Drain Current

Rds(on)

Duty Cycle

MOSFET Temperature Factor

Drain-Source Voltage During Switching

Rise Time

Fall Time

Switching Frequency

Gate Charge Qg

Gate Drive Voltage

Thermal Resistance θJA / θTotal

Ambient Temperature

Conduction loss uses hot Rds(on): I² × Rds × duty. Switching loss uses 0.5 × V × I × (tr + tf) × frequency.

Presets:low-side 12Vbuck MOSFETmotor PWM

Total MOSFET Power Loss

Thermal Resistance

Ambient Temperature

Max Junction Temperature

Use this when you already know MOSFET total dissipation and want to estimate junction temperature.

Drain Current

Allowed Conduction Loss

Duty Cycle

Hot Rds Factor

This estimates the maximum room-temperature Rds(on) you should select for a target conduction loss.

📐 Formula Reference

Conduction Loss

Pcond = I² × Rds(on) × duty

Switching Loss

Psw ≈ 0.5 × VDS × ID × (tr + tf) × f

Gate Drive Loss

Pgate = Qg × Vdrive × f

Junction Temperature

Tj = Tamb + Ploss × θJA

📋 Quick Reference

Loss Type

DC / low frequencyconduction

High PWMswitching

Gate driverQg loss

Reduce Heat

Lower Rds(on)cooler

Faster switchingless Psw

Better PCB copperlower θ

Check Datasheet

Rds vs tempimportant

SOApulse

Thermal resistancepackage

📚 Engineering Notes

Rds(on) increases when hotDatasheet Rds(on) is often given at 25°C. In real circuits, hot Rds(on) can be significantly higher.

Switching loss matters at high frequencyAt high PWM frequency, switching loss can dominate even when conduction loss looks small.

Gate resistor affects switching lossUse the MOSFET Gate Resistor Calculator to estimate switching speed and gate current.

PCB copper is the heatsinkFor SMD MOSFETs, PCB copper and airflow strongly affect junction temperature. Check trace width and thermal copper area.

What is a MOSFET Power Loss Calculator?

A MOSFET power loss calculator estimates how much heat a MOSFET dissipates during conduction and switching. It helps select MOSFETs, gate drivers, PCB copper and heatsinking for power circuits.

How MOSFET conduction loss is calculated

Conduction loss is calculated using current squared multiplied by Rds(on) and duty cycle. Hot Rds(on) should be considered because MOSFET resistance increases with temperature.

How MOSFET switching loss is calculated

Switching loss is estimated from drain-source voltage, drain current, rise time, fall time and switching frequency. Faster switching reduces switching loss, but may increase ringing and EMI.

Important limitation

This calculator gives a practical estimate. Final design should use MOSFET datasheet curves, gate driver capability, PCB layout, safe operating area, measured switching waveforms, thermal testing and heatsink/PCB thermal design.

❓ Frequently Asked Questions

A MOSFET gets hot due to conduction loss from Rds(on), switching loss during transitions, gate drive loss and sometimes body diode or reverse recovery losses.

Lower Rds(on) reduces conduction loss, but MOSFETs with very low Rds(on) may have higher gate charge, which can increase switching and gate drive requirements.

It depends on total power loss and thermal resistance. SMD MOSFETs often use PCB copper as the heatsink.