MOSFET Gate Charge Loss

Estimate gate-drive power from Qg, Vdrive, and fsw. Outputs energy-per-cycle, average gate current, and total gate-drive power.

How to Use

  1. Enter MOSFET total gate charge Qg from the datasheet (typically at a stated Vgs).
  2. Enter your gate-drive voltage Vdrive (e.g., 10V or 12V) and switching frequency fsw.
  3. Set how many MOSFET gates are being driven (total devices driven at that frequency).
  4. Check “Show Work” to verify units and see the exact equations used.
Gate Drive Lab View
Energy per cycle, average gate current, and power at your switching frequency.
E/cycle
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Iavg
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Pgate
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Total
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Flag: —
Gate Driver Vdrive fsw Rg MOSFET Qg (total) Gate capacitance equiv. Core: E = Qg × Vdrive, P = Qg × Vdrive × fsw
Inputs & Settings
Enter datasheet Qg, drive voltage, and switching frequency. Add device count for totals.
Use datasheet “Total Gate Charge” at a stated Vgs (often 10V). Typical: 5–300nC
Common: 5V, 8V, 10V, 12V, 15V (depends on MOSFET + driver)
Typical ranges: 20kHz (motor) • 100–500kHz (SMPS) • 1–5MHz (fast DC/DC)
Total gates driven at this fsw (e.g., half-bridge = 2 MOSFETs)
Optional: used for informational notes only (does not change ideal Qg loss equation)
Optional: included for context in notes (Qg loss is per switching event, not duty)
Show Work (step-by-step)
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Work is shown in base units (C, V, Hz, A, W) for clarity and consistency.

Gate Charge Loss Formulas

The ideal gate-drive energy per switching cycle is: E = Qg × Vdrive

  • Energy per cycle: E = Qg × Vdrive
  • Average gate current: Iavg = Qg × fsw
  • Gate-drive power (per device): Pgate = Qg × Vdrive × fsw
  • Total power (N devices): Ptotal = N × Pgate
Where Qg = coulombs (C), Vdrive = volts (V), fsw = hertz (Hz), E = joules (J), P = watts (W).

FAQ

Is gate charge loss “MOSFET loss” or “driver loss”?

It’s power drawn from the gate driver supply to charge and discharge the MOSFET gate each cycle. It mostly heats the driver/output stage and gate network (and some is dissipated in the MOSFET’s gate structure).

Does duty cycle change Qg loss?

In the ideal model, no — the gate is charged/discharged per switching event, so the main driver is switching frequency. Duty cycle matters more for conduction loss, not gate-charge power.

Which Qg should I use from the datasheet?

Use the Total Gate Charge (Qg) at the Vgs you’re actually driving (often 10V). If your driver voltage differs, Qg may differ too; datasheets usually include a Qg vs Vgs curve.

What about Miller plateau / Qgs / Qgd?

Total Qg already includes those regions. This tool uses total Qg for a clean first-order estimate. For edge timing, switching node dv/dt, and EMI, you’d model Qgd + gate resistor + driver current limits.

Tool Info

Last updated:

Updates may include additional unit presets, driver notes, and edge-case handling for extreme frequencies/charges.