Calculate MOSFET gate resistor value, gate driver current, switching time, gate power and approximate switching loss for low-side switches, PWM drivers, buck converters and motor drivers.
Gate current is approximately Qg / switching time. Gate resistor is estimated from drive voltage divided by gate current, minus driver and MOSFET internal resistance.
Presets:logic MOSFETpower MOSFETfast PWM
Gate Drive Voltage
Gate Charge Qg
External Gate Resistor
Driver Resistance
Internal Gate Resistance
This estimates switching time from total gate resistance and gate charge. Real switching depends on Miller plateau, driver strength and circuit layout.
Drain-Source Voltage
Drain Current
Rise Time
Fall Time
Switching Frequency
Gate Charge Qg
Gate Drive Voltage
This gives a rough switching-loss estimate. Use the MOSFET datasheet and real waveforms for final design.
Gate charge matters more than gate capacitanceFor switching calculations, MOSFET total gate charge Qg is often more practical than capacitance alone.
Gate resistor is a tuning partStart with a calculated value, then verify ringing, EMI and temperature on the real circuit.
Switching speed affects heatSlower switching can reduce ringing but increases switching loss. Use the MOSFET Power Loss Calculator next.
Use a real gate driver for power MOSFETsMicrocontroller pins may not provide enough current for large MOSFETs at high PWM frequency.
What is a MOSFET Gate Resistor Calculator?
A MOSFET gate resistor calculator estimates the external gate resistor needed to achieve a desired switching time from gate charge and drive voltage. It also estimates gate current, switching time, gate drive power and rough switching loss.
Why MOSFETs need a gate resistor
The gate resistor controls the charging and discharging speed of the MOSFET gate. It helps reduce ringing, overshoot and EMI, but a value that is too high can make switching slow and increase heat.
How gate resistor value is calculated
The calculator estimates gate current from Qg divided by desired switching time. It then estimates total resistance from gate drive voltage divided by gate current and subtracts driver output resistance and MOSFET internal gate resistance.
Important limitation
This calculator is a practical starting point. Final gate resistor value should be verified with oscilloscope measurements, MOSFET datasheet curves, gate driver capability, PCB layout, load type, snubbers and thermal testing.
â Frequently Asked Questions
The MOSFET switches faster, but it can cause ringing, overshoot, EMI and stress on the gate driver.
The MOSFET switches slower, which can increase switching loss and heat, especially in PWM applications.
For small low-frequency loads it may work, but power MOSFETs at high PWM frequency usually need a dedicated gate driver.