MOSFET Switching Loss

Formula

Description

During each switching transition, the MOSFET passes through its linear region where both significant voltage and current exist simultaneously, causing power dissipation. The energy lost per transition is approximated as a triangle with peak power V × I and duration equal to the rise or fall time. Total switching loss scales linearly with frequency, making it the dominant loss mechanism at high switching frequencies. Gate driver strength and MOSFET gate charge directly determine the transition times and thus the switching losses.

Variables

• P — Average switching power loss (W)
• V — Drain-source voltage being switched (V)
• I — Drain current being switched (A)
• tr — Turn-on rise time (s)
• tf — Turn-off fall time (s)
• f — Switching frequency (Hz)

Practical Notes

This simplified model does not account for reverse recovery of the body diode, output capacitance losses (Coss), or gate charge losses. For hard-switched applications, total MOSFET loss = conduction loss + switching loss + gate drive loss. Soft-switching topologies (ZVS/ZCS) can nearly eliminate switching losses.