Gate drive power and gate resistance calculator
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KEY POINTS
Gate drive power is Pg = Qg × (V+ − V−) × fsw; it depends on gate charge, voltage swing and frequency, not on the gate resistor. The gate resistor is the knob that sets peak current and switching speed: smaller values cut loss but add surges and noise. SiC MOSFETs are commonly driven with a −2 to −5 V negative bias when off to prevent false turn-on.
Inputs
Gate capacitance depends strongly on voltage, so read Qg from the datasheet gate charge curve (Qg–Vgs) over the V+ and V− range you actually use. Transition times approximate Qgd being charged or discharged at a constant current during the plateau.
External gate resistance and switching speed
| Rg,ext | Peak current | Turn-on transition | Turn-off transition |
|---|---|---|---|
| 0 Ω | 7.33 A | 7.5 ns | 6.3 ns |
| 2 Ω | 4.40 A | 12.5 ns | 10.4 ns |
| 5 Ω | 2.75 A | 20.0 ns | 16.7 ns |
| 10 Ω | 1.69 A | 32.5 ns | 27.1 ns |
| 20 Ω | 0.96 A | 57.5 ns | 47.9 ns |
Choosing the gate resistance
The gate of a power MOSFET or IGBT is a capacitive load that takes in and gives back the charge Qg at every switching event. A smaller gate resistance raises gate current and speeds up switching, cutting switching loss, but larger dV/dt and dI/dt cause voltage surges, noise (EMI) and false turn-on. Gate resistance is the knob that trades loss against noise.
SiC MOSFETs have a low threshold voltage, and high dV/dt can lift the gate through the Miller capacitance and turn the device on falsely, so a negative bias of −2 to −5 V is commonly applied when off. GaN HEMTs have a low gate voltage rating (around +6 V) and very small Qg, so precise driver output voltage and low parasitic inductance in the gate loop become critical.
FAQ
Does the gate resistor change gate drive power?
No. Total gate drive power is Qg × voltage swing × frequency. The resistor only decides how that power is shared between the driver and the resistor and how fast the device switches.
Why use a negative gate voltage for SiC MOSFETs?
SiC MOSFETs have a low threshold voltage, and high dV/dt can couple through the Miller capacitance and turn the device on falsely. A negative off-state bias adds margin.
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Last updated: October 23, 2026