Half-Bridge Dead Time

Formula

Description

In a half-bridge or full-bridge circuit, dead time is the mandatory delay between turning off one MOSFET and turning on the other to prevent shoot-through (both transistors on simultaneously, creating a short circuit from supply to ground). The minimum dead time must exceed the turn-off time of the MOSFET, which is dominated by the Miller plateau where the gate driver must remove the gate-drain charge Qgd. The actual dead time should include safety margin (typically 2-3x the calculated minimum) to account for component variation and temperature effects.

Variables

• t_dead — Minimum dead time (s)
• Q_gd — MOSFET gate-drain (Miller) charge (C)
• I_gate — Gate driver sink current (A)

Practical Notes

Typical dead times: 50-200 ns for silicon MOSFETs, 20-50 ns for GaN FETs. During dead time, the inductor current flows through the body diode (or reverse channel in GaN), causing conduction loss and reverse recovery loss. Excessive dead time increases body diode loss and distorts the output waveform. Adaptive dead time control in modern gate drivers optimizes this trade-off automatically.