MOSFET Gate Resistor
Compute the external gate resistor from drive voltage, gate charge, Miller charge, and target switching time; check peak drive current, drive power, and resistor dissipation.
Key points
MOSFET Gate Resistor: Compute the external gate resistor from drive voltage, gate charge, Miller charge, and target switching time; check peak drive current, drive power, and resistor dissipation. Formula: Rg_ext = Vdrive·t_sw/Qgd − Rg_int ｜ Ipk = Vdrive/(Rg_ext + Rg_int) ｜ P_drive = Qg·Vdrive·fsw. Enter parameters on the DD-CAT IDE online tool page to get results instantly, with a calculation-model diagram that updates with the inputs. A larger gate resistor slows switching and reduces EMI but increases loss. Use separate turn-on / turn-off resistors (with a Schottky diode) for asymmetric edges. Actual switching time is set by Qgd and drive current; Qg only estimates full charge time. Qgd is the more critical datasheet parameter.
Inputs
Rg_ext = Vdrive·t_sw/Qgd − Rg_int ｜ Ipk = Vdrive/(Rg_ext + Rg_int) ｜ P_drive = Qg·Vdrive·fswCalculation model (updates with parameters)
| Recommended external gate resistor Rg_ext | 22 Ω | ideal 23 Ω, by E12 nearest value |
| From Miller charge Qgd | 23 Ω | 决定Switch平台 / 实际沿Time |
| From total gate charge Qg | 4.667 Ω | 决定完整充DischargeTime |
| Peak gate current Ipk | 416.7 mA | Vdrive/(Rg_ext + Rg_int) |
| Average drive power | 30 mW | Qg·Vdrive·fsw |
| External resistor dissipation | 27.5 mW | 按驱动Power在 Rg_ext / (Rg_ext+Rg_int) 上的分压 |
| Estimated switching loss (on + off) | 480 mW | 0.5·Vds·Id·2t_sw·fsw（近似） |
| Actual switching edge time | 20 ns | 由 Rg_ext and Qgd 决定 |
Engineering notes
- A larger gate resistor slows switching and reduces EMI but increases loss. Use separate turn-on / turn-off resistors (with a Schottky diode) for asymmetric edges.
- Actual switching time is set by Qgd and drive current; Qg only estimates full charge time. Qgd is the more critical datasheet parameter.
- Keep the gate loop small and place Rg close to the gate. Add a totem-pole / dedicated gate driver when drive is insufficient; avoid driving a large MOSFET directly from an MCU pin.
FAQ
- What is MOSFET Gate Resistor for?
- Compute the external gate resistor from drive voltage, gate charge, Miller charge, and target switching time; check peak drive current, drive power, and resistor dissipation.
- What is the formula for MOSFET Gate Resistor?
- Core formula: Rg_ext = Vdrive·t_sw/Qgd − Rg_int ｜ Ipk = Vdrive/(Rg_ext + Rg_int) ｜ P_drive = Qg·Vdrive·fsw. The tool returns results instantly using this formula and the selected parameters.
- What engineering notes should I keep in mind when using MOSFET Gate Resistor?
- A larger gate resistor slows switching and reduces EMI but increases loss. Use separate turn-on / turn-off resistors (with a Schottky diode) for asymmetric edges. Actual switching time is set by Qgd and drive current; Qg only estimates full charge time. Qgd is the more critical datasheet parameter. Keep the gate loop small and place Rg close to the gate. Add a totem-pole / dedicated gate driver when drive is insufficient; avoid driving a large MOSFET directly from an MCU pin.