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MOSFET Power Dissipation Calculator

Work out mosfet power dissipation instantly with clear inputs, formula shown and shareable results.

About MOSFET Power Dissipation Calculator

MOSFET loss has two parts: conduction loss I squared times Rds(on), and switching loss equal to the energy lost per transition times the switching frequency. Low frequency designs are dominated by conduction, high frequency ones by switching, and the balance decides whether to pick a low-Rds or low-charge device.

Formula

MOSFET losses

P = Id^2 x Rds(on) + Esw x fsw

Worked example

With the default values below, MOSFET Power Dissipation Calculator returns Total power dissipation of 3.40. Change any input above and every figure here is recalculated in your browser.

Inputs used

Drain current
8 A
On resistance
25 mΩ
Switching energy per cycle
18 µJ
Switching frequency
100 kHz

Results

Total power dissipation
3.40 W
Conduction loss
1.60 W
Switching loss
1.80 W
Switching share of loss
52.9% %

Step by step

  1. 1Values used
  2. 2MOSFET losses
  3. 3Total power dissipation= 3.40 W
  4. 4Conduction loss= 1.60 W
  5. 5Switching loss= 1.80 W
  6. 6Switching share of loss= 52.9 %

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or fees or charges into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

Frequently Asked Questions

Why does Rds(on) matter less at high frequency?

Because switching loss grows linearly with frequency while conduction loss does not change, so gate charge and transition speed dominate above a few hundred kilohertz.

Should I use hot or cold Rds(on)?

Hot. Rds(on) typically rises 30-80% from 25 to 100 degrees C, so use the datasheet value at the expected junction temperature.

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