MOSFET Gate Resistor Calculator

Total gate charge, Qg (nC)

Use the datasheet total gate charge at your chosen Vgs.

Driver voltage, Vdrv (V)

This is the applied gate drive amplitude.

Driver output resistance, Rdrv (Ω)

Use the driver’s typical source/sink resistance, if known.

Internal gate resistance, Rg,int (Ω)

From MOSFET datasheet, or leave as 0.

Target turn-on time, tON (ns)

Approximate rise-time or turn-on edge target.

Target turn-off time, tOFF (ns)

Approximate fall-time or turn-off edge target.

Max turn-on peak current, Ipk,ON (A)

Optional. Limits gate current to reduce stress and ringing.

Max turn-off peak current, Ipk,OFF (A)

Optional. Often higher sink current is acceptable.

Calculate Reset

Tip: If you use separate on/off resistors with a diode, apply the computed external values per edge.

This calculator uses a charge-based approximation for MOSFET gate drive.

• Gate current from charge and time: I ≈ Qg / t
• Total series resistance: Rtotal ≈ Vdrv / I
• Time-based resistance: Rtime ≈ Vdrv · t / Qg
• Current-limit resistance: Rcurrent ≈ Vdrv / Ipk,max
• External resistor: Rg,ext = max(0, Rtotal − Rdrv − Rg,int)

The model is intentionally simple for early sizing. Final tuning should be verified with real waveforms.

1. Enter MOSFET total gate charge Qg from the datasheet.
2. Enter gate drive voltage Vdrv your driver applies.
3. Add driver output resistance Rdrv if known.
4. Add internal gate resistance Rg,int, or leave zero.
5. Set target tON and tOFF to shape switching.
6. Optionally set peak current limits for gentler edges.
7. Press Calculate and review the recommended resistors.
8. Export results using the CSV and PDF buttons.

For EMI control, start higher, then reduce while monitoring ringing and temperature.

Values are illustrative. Validate with your exact parts and layout.

1) Why the gate resistor matters

The MOSFET gate is a capacitive node that needs current every cycle. A gate resistor sets that current, controlling dv/dt and di/dt, which impacts EMI, ringing, and overshoot. It also reduces driver stress and helps protect the gate oxide during fast transitions.

2) Using Qg as the key datasheet input

Datasheets list total gate charge Qg (nC) for specific test conditions. Qg estimates how much charge must be moved to reach the intended gate state. Larger Qg requires more drive effort, especially at high switching frequency where charge is transferred repeatedly.

3) Relating charge, time, and current

A practical sizing step is I ≈ Qg / t. For example, 80 nC over 50 ns implies about 1.6 A. Waveforms are not perfectly rectangular, but this estimate is useful for first-pass resistance selection and for checking whether a driver is strong enough.

4) Converting current to resistance

With driver voltage Vdrv, approximate series resistance is R ≈ Vdrv / I. Remember the driver output resistance and MOSFET internal gate resistance are already in series. The external part is Rg,ext = max(0, Rtotal − Rdrv − Rg,int), which is your tuning knob.

5) Different values for turn-on and turn-off

Turn-on and turn-off often benefit from different speeds. Slower turn-on can reduce drain ringing and emissions, while faster turn-off can cut shoot-through and improve fault response. A diode plus two resistors is commonly used to independently tune each edge without changing the driver.

6) Peak current limits and feasibility

Low resistance can produce large peak gate current, causing ground bounce and ringing. Adding a peak-current limit helps robustness and driver reliability. If the current limit demands more resistance than your time target allows, relax the target, accept a slower edge, or choose a stronger driver.

7) Miller plateau and measured behavior

During the Miller plateau, gate charge mainly moves the drain voltage rather than raising Vgs, so measured timing can differ from simple estimates. Treat the calculated resistor as a starting point, then verify with scope probes on Vgs and Vds while monitoring overshoot and ringing.

8) Practical ranges and refinement workflow

Many designs start with external gate resistors around 1–10 Ω, increasing for very fast drivers or longer gate traces. Begin conservatively, then adjust in small steps while checking temperature, switching loss, and emissions. Place the resistor near the gate pin and keep the return loop tight.

1) Which Qg value should I use?

Use the datasheet total gate charge at the closest Vgs and operating current. If multiple curves exist, pick the worst-case or the curve nearest your drain current and Vds conditions.

2) What if I only know the driver peak current rating?

Enter that rating as the peak current limit. The calculator will size resistance to keep peak gate current at or below that value, then it estimates the resulting edge time.

3) Why do I get “infeasible” for a target time?

It means your current limit demands a resistance that would make the edge slower than the requested time. Relax the time target, raise the allowed current, or select a stronger driver and lower total series resistance.

4) Do I need different resistors for turn-on and turn-off?

Not always, but separate values can improve EMI and reduce ringing while keeping good fault response. A diode plus two resistors is common when turn-off must be faster than turn-on.

5) Where should the gate resistor be placed?

Place the external resistor as close as possible to the MOSFET gate pin. This minimizes the loop inductance and improves damping of ringing caused by trace and package parasitics.

6) Can a gate resistor reduce switching loss?

Usually, higher resistance increases switching loss by slowing transitions. However, proper damping can reduce ringing and overshoot, which sometimes improves overall efficiency and reliability in noisy layouts.

7) What resistor power rating is needed?

Gate resistors typically dissipate little average power, but check switching frequency and gate charge. Estimate energy per cycle as Qg·Vdrv, then multiply by frequency to approximate driver-related power.