Why are conduction loss and switching loss shown separately instead of one total?

They come from different physics and respond to different design changes. Conduction loss scales with Rds(on) and duty cycle; switching loss scales with voltage, current, transition time, and frequency. Blending them into one number hides which lever actually reduces heat.

What is the conduction loss formula used here?

Conduction loss = I^2 x Rds(on) x duty cycle, where I is drain current in amps, Rds(on) is on-resistance in ohms, and duty cycle is the on-time fraction (0 to 1).

What is the switching loss formula used here?

Switching loss = 0.5 x V x I x (tr + tf) x switching frequency, where V is the blocking voltage, I is drain current, tr and tf are rise and fall time, and frequency is in hertz. This is the standard linear-transition approximation.

Where do I find Rds(on), rise time, and fall time?

All three are in the MOSFET datasheet, usually under electrical characteristics. Rds(on) depends on gate voltage and temperature, so use the value at your actual drive voltage and expected junction temperature, not the 25C minimum.

Does this include gate drive loss or reverse recovery loss?

No. This calculator covers conduction loss and turn-on/turn-off switching loss only. Gate charge loss, diode reverse recovery, and output capacitance (Coss) loss are separate terms not included here.

Why does switching loss grow faster than conduction loss at high frequency?

Conduction loss does not depend on frequency at all, only on RMS current and duty cycle. Switching loss is directly proportional to frequency, since every extra switching cycle adds another turn-on and turn-off transition.

MOSFET Power Dissipation Calculator

Name: MOSFET Power Dissipation Calculator
Availability: InStock
Author: Nham Vu

Enter drain current, Rds(on), duty cycle, voltage, switching times and frequency to split MOSFET losses into conduction and switching, plus the total.

MOSFET Operating Parameters

Drain Current (A)

Rds(on) (milliohms)

Duty Cycle (%)

Supply Voltage (V)

Rise Time (ns)

Fall Time (ns)

Switching Frequency (kHz)

Power Dissipation Breakdown

Conduction Loss

0.00 W

I² × Rds(on) × duty cycle

Switching Loss

0.00 W

0.5 × V × I × (tr+tf) × f

Total Power Dissipation

0.00 W

Conduction Switching

Summary

Enter drain current, Rds(on), duty cycle, voltage, switching times and frequency to split MOSFET losses into conduction and switching, plus the total.

How it works

Enter the drain current the MOSFET carries while conducting.
Enter Rds(on) from the datasheet at the expected junction temperature.
Enter the duty cycle, the fraction of each switching period the MOSFET is on.
Enter the supply (drain) voltage the MOSFET blocks when off.
Enter rise time and fall time from the datasheet or a scope measurement.
Enter the switching frequency; the calculator computes conduction loss, switching loss, and their sum.

Use cases

Sizing a heatsink for a buck or boost converter MOSFET.
Comparing two MOSFETs with different Rds(on) and switching-time tradeoffs.
Checking whether a design is conduction-limited or switching-limited before changing frequency.
Estimating losses when raising switching frequency to shrink an inductor.
Verifying a MOSFET selection against a thermal budget before a board spin.
Teaching the difference between conduction and switching loss in a power electronics course.

Frequently Asked Questions

Last updated: 2026-07-21 · Reviewed by Nham Vu