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MOSFET Switching Loss Calculator

Enter the voltage, current, switching times and frequency to get the switching loss.

How it is calculated

The tool uses the linear-overlap approximation P = 0.5 × Vds × Id × (t_on + t_off) × fsw. Vds is the drain-source voltage in volts, Id the drain current in amperes, t_on and t_off the turn-on and turn-off times in nanoseconds, and fsw the switching frequency in kilohertz. The engine converts the times (×10-9) and frequency (×103) to seconds and hertz, then prints watts with four decimals. Negative or missing values give no result. It models only switching loss; conduction loss (Id² × Rds(on)), gate-drive loss and diode recovery are not included, so add them for a full thermal budget.

Worked example

Take Vds = 48 V, Id = 10 A, t_on = 20 ns, t_off = 30 ns and fsw = 100 kHz. The transition time is 20 + 30 = 50 ns = 5 × 10-8 s, and the frequency is 100 000 Hz. Energy per cycle: 0.5 × 48 × 10 × 5 × 10-8 = 1.2 × 10-5 J. Multiply by 100 000 cycles per second and the switching loss is 1.2000 W.

Try this example →

Common mistakes

  • Entering times in microseconds or seconds: the fields expect nanoseconds, so 0.05 for 50 ns makes the loss a thousand times too small.
  • Entering the frequency in hertz (100000) instead of kilohertz (100), which inflates the loss by a factor of 1000.
  • Using the supply voltage and the average current rather than the voltage and current actually present across and through the device at the switching instant.
  • Treating the result as the total MOSFET dissipation, when conduction loss and gate-drive loss still have to be added.
  • Entering only one transition time, or the datasheet rise/fall time instead of the real voltage-current overlap time in the circuit.

About this calculator

A MOSFET doesn't switch on or off instantaneously — during the brief turn-on and turn-off transition times (t_on, t_off), it's simultaneously carrying significant current and dropping significant voltage, dissipating energy as heat. The switching power loss is approximated as P = 0.5 · Vds · Id · (t_on + t_off) · fsw, where Vds and Id are the blocking voltage and conducted current, and fsw is the switching frequency — meaning loss scales linearly with how fast you switch the device.

Power electronics engineers calculate this when designing switch-mode power supplies, motor drives, and DC-DC converters, since switching loss (together with conduction loss) determines how much heatsinking a MOSFET needs and sets a practical ceiling on how high the switching frequency can go before efficiency and thermal limits are exceeded.

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