MOSFET Gate Drive Power

Formula

Description

Every switching cycle, the MOSFET gate capacitance must be charged to Vgs and then discharged back to zero. The energy per cycle is Qg × Vgs, and multiplying by the switching frequency gives the average power dissipated in the gate driver circuit. This power is independent of the drain current and is dissipated entirely in the gate driver (not in the MOSFET itself). At high switching frequencies with large MOSFETs (high Qg), gate drive losses can become significant and must be included in the total loss budget.

Variables

• Pd — Average gate drive power loss (W)
• Qg — Total gate charge per switching cycle (C)
• Vgs — Gate drive voltage (V)
• f — Switching frequency (Hz)

Practical Notes

Typical Qg values: small signal MOSFET 1-10 nC, medium power 10-50 nC, high power 50-500 nC. Gate drive power comes from the gate driver supply, not the power stage. Half-bridge gate drivers need bootstrap capacitors for the high-side gate. GaN transistors have much lower Qg than silicon for the same Rds(on), enabling higher switching frequencies.