MOSFET Gate Driver Resistor Calculator
Calculate gate resistor (Rg) for a target switching rise time. Find Ciss in your MOSFET datasheet under "Capacitances" at your operating Vds.
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Gate Resistor Design Explained
The gate resistor controls how fast the MOSFET turns on and off. A lower Rg means faster switching and lower switching losses, but higher dV/dt and dI/dt which can cause EMI, ringing, and voltage overshoot. Choosing the right Rg is a tradeoff between switching losses and EMI/overshoot.
Rise Time Formula
Rg = tr / (2.2 × Ciss)
This is the standard RC 10%–90% rise time formula. The factor 2.2 comes from ln(9) ≈ 2.197 for an RC charging circuit. Ciss is the input capacitance from the MOSFET datasheet (Cgs + Cgd with drain shorted to source). Note: the actual gate charge behavior is non-linear due to the Miller plateau, so treat this as a first-order estimate.
Gate Drive Power Loss
P_gate = Ciss × Vdrv² × f
This is the energy dissipated charging and discharging the gate capacitance each switching cycle. It is independent of Rg — Rg only determines where the loss occurs (in the resistor vs. the driver IC). A 1000pF gate, 12V drive, 500kHz switching dissipates approximately 72mW.
Where to Find Ciss in the Datasheet
Look for the "Capacitance vs. Drain-to-Source Voltage" curve in the MOSFET datasheet. Use the Ciss value at your actual operating Vds — capacitance drops significantly as Vds increases. Many designers use the Ciss at Vds = 0V (worst case) for conservative estimates.
Separate Turn-On and Turn-Off Resistors
In half-bridge and full-bridge designs, it is common to use separate gate resistors for turn-on (Rg_on) and turn-off (Rg_off) using a diode. A higher Rg_on slows the turn-on (reducing dI/dt and current ringing), while a lower Rg_off allows fast turn-off (reducing conduction losses in the body diode).
Frequently Asked Questions
What is a typical gate resistor value?
Values typically range from 2Ω to 33Ω. Low-voltage MOSFETs (<100V) often use 4.7–10Ω. High-voltage IGBTs and SiC MOSFETs often need 10–47Ω to prevent oscillation due to higher parasitic inductances in the package.
Can I use 0Ω for the gate resistor?
Rarely. Without any resistance, the gate current is limited only by the driver output impedance and PCB parasitic inductance, which can cause high-frequency oscillation and damage the gate driver. Most designs have at least 1–2Ω in series with the gate.