MOSFET Body Diode Loss

Formula

Description

The MOSFET body diode conducts during dead time in half-bridge and full-bridge circuits when the inductor current forces through the antiparallel diode before the complementary switch turns on. The loss depends on the diode forward voltage drop (typically 0.7-1.2 V for silicon MOSFETs), the current magnitude, and the fraction of the switching period spent in diode conduction (approximately 1 − D for the low-side switch, or proportional to dead time). Body diode losses are significant in synchronous rectifiers and motor drives, especially at low duty cycles.

Variables

• P — Body diode conduction loss (W)
• V_f — Body diode forward voltage (V)
• I_f — Current through the body diode (A)
• D — Duty cycle of the MOSFET channel conduction (0 to 1)

Practical Notes

GaN FETs do not have a true body diode but have a reverse conduction mode with higher voltage drop (2-3 V) and zero reverse recovery charge. Schottky diodes placed in parallel with the body diode can reduce the forward voltage and eliminate reverse recovery loss in silicon MOSFETs. In synchronous buck converters, the body diode conducts only during dead time (typically < 1% of the period), so this loss is usually small.