Power Electronics

MOSFET Loss & Thermal Calculator

Accurately estimating MOSFET losses requires understanding two distinct phases: Conduction ($I^2R$ losses) and Switching (VI overlap losses).

Use Direct Input if you know your RMS and Switching currents. Use the Topology Wizard to automatically derive these values for standard Buck or Boost converters.

MOSFET Datasheet

Specs
mΩ
ns
ns
°C/W
°C

Switching Conditions

Circuit
V
kHz
A
A
A

Loss Breakdown

Analysis
Total Power Loss
— W
Cond: — Switching: —
Estimated Junction Temp
— °C
Enter parameters
Switching Overlap
Vds Id Turn On Turn Off

Formulas Explained

Conduction Loss

Pcond = Irms2 × RDS(on)

Note: The calculator applies a 1.5x multiplier to RDS if “Simulate Hot” is checked.

Switching Loss

Psw = 0.5 × VDS × fsw × (Iontr + Iofftf)

Energy lost during the rise/fall transition overlap.

Buck RMS Current

Irms ≈ Iout × √D

Approximation used in the Wizard for High-Side switches.

Boost RMS Current

Irms ≈ (Iout / (1-D)) × √D

Approximation used in the Wizard for Low-Side switches.

How to Use

Two ways to use this tool:

A

Option 1: Direct Input

If you already have your circuit simulation values, simply enter RDS(on), Irms, and switching times. This works for any topology.

B

Option 2: Topology Wizard

Click “Topology Wizard”. Select Buck or Boost, enter your voltage/load, and click Apply. We will calculate the RMS currents for you.

3

Check Temperature

Review the Junction Temp. If it’s red (>125°C), you need a better MOSFET, a heatsink, or a lower switching frequency.