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MOSFET Power Loss

A switching FET loses power three ways: conduction (I²·R_ds(on)), switching (overlap of voltage and current during transitions) and gate drive (Q_g·V_gs·f). Conduction dominates at low frequency, switching at high.

RMS drain current (A)

Rds(on) (mΩ)

Switched voltage (V)

Switched current (A)

Rise time (ns)

Fall time (ns)

Gate charge Qg (nC)

Gate drive (V)

Switching frequency (kHz)

θ junction-ambient (°C/W)

Ambient (°C)

Conduction loss

—

Switching loss

—

Gate loss

—

Total loss

—

Junction temp

—

Rds(on) rises sharply with temperature (often 1.5–2× at 125 °C) — iterate, or use the hot value. Gate loss is burned in the driver, not the FET.

A helper, not a substitute for engineering judgment. Verify against the governing standard.