Electrical & Electronics
MOSFET Loss & Gate Drive Calculator
Estimate DC or PWM conduction and switching losses, gate-drive power and charging current.
Your inputs
Your results
- Transistor dissipation estimate
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- Conduction loss
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- Switching loss estimate
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- Gate-drive power
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- Average gate supply current
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- Charging current estimate
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—Estimate MOSFET heat and gate-drive requirements separately
Estimate conduction and switching loss for a MOSFET carrying constant on-state current in DC or PWM operation. Add gate-charge data to estimate gate-drive power and current. The model applies a resistance factor you enter and a first-order hard-switching overlap calculation. It excludes body-diode loss, reverse recovery, output-capacitance loss, parasitic ringing and the actual current waveform in an inductive circuit.
Step by step
- Choose DC or PWM. Enter switched voltage VDS in V, on-state current in A, RDS(on) in mΩ and a positive resistance temperature factor. Use resistance appropriate to the actual gate voltage; the gate-drive voltage field does not automatically correct RDS(on).
- For PWM, enter duty percentage, frequency in kHz and rise and fall times in ns. Enter gate charge Qg in nC, gate-drive voltage VGS in V and target gate charging time in ns. Use compatible device and operating-condition data.
- Compare conduction loss, switching loss and their transistor dissipation total. Review gate-drive power and both current estimates separately. Use the existing thermal-calculator link to transfer transistor dissipation, then supply thermal resistances and ambient conditions for that device and assembly.
Settings and limits
- On-current and resistance factor
- Conduction loss is current squared times entered RDS(on), temperature factor and duty fraction. Current is the value during the on interval, not the PWM average. The factor multiplies resistance directly; the calculator does not determine it from temperature or iterate between electrical loss and junction temperature.
- Switching and PWM endpoints
- For continuously switching PWM, overlap loss is approximately half the switched voltage times on-current, the sum of rise and fall times and frequency. Rise time must fit inside the on interval and fall time inside the off interval. DC and duty endpoints of 0% or 100% have no continuous switching loss in this model.
- Gate power and charging current
- Gate-drive power is Qg × VGS × frequency and average gate supply current is Qg × frequency. Qg divided by target charging time estimates average current during charging, not a guaranteed peak driver current. Gate-drive power is shown separately and is not added to the transistor heat transferred by the link.
Worked example
Choose PWM with 12 V, 5 A on-current, 20 mΩ RDS(on), resistance factor 1.5, 50% duty and 20 kHz. Use 30 ns rise and fall times, Qg = 25 nC, VGS = 10 V and 100 ns charging time. Effective resistance is 30 mΩ.
| f | D | Pcond | Psw | PFET | Pgate |
|---|---|---|---|---|---|
| 20 kHz | 50% | 0.375 W | 0.036 W | 0.411 W | 0.005 W |
| 100 kHz | 50% | 0.375 W | 0.18 W | 0.555 W | 0.025 W |
| DC | 100% | 0.75 W | 0 W | 0.75 W | 0 W |
Conduction loss is 0.375 W and switching loss 0.036 W, giving transistor heat 0.411 W. Gate-drive power is 0.005 W, average gate supply current 0.5 mA and charging-current estimate 0.25 A. Increasing only frequency to 100 kHz raises transistor heat to 0.555 W and gate-drive power to 0.025 W; conduction loss is unchanged.
Questions and troubleshooting
Can I use average load current for the PWM current input?
The equation expects constant on-state current and applies duty separately. Entering duty-averaged current would reduce that current again through the model and underestimate conduction loss. Ripple or varying current requires an appropriate RMS-current or waveform-based calculation outside this tool.
Why is gate-drive power zero at full duty?
The model treats full duty as continuously on, with no repeated charging cycles, and zero duty as continuously off. Startup charging and leakage are not included. Transition-time validation applies only when duty lies strictly between the two endpoints.
Does a small loss result prove a MOSFET or driver is suitable?
Check voltage and current ratings, safe operating area, gate-voltage limits, driver capability and thermal conditions for the actual parts. The estimates depend on supplied resistance, gate charge and switching times; a low modeled loss does not validate those device-specific limits.