MOSFET Efficiency Calculator
Estimate MOSFET power-stage efficiency by combining on-state conduction loss, voltage-current switching overlap, and gate-drive power.
Use the loss breakdown to compare device and operating choices, then account separately for inductors, diodes, drivers, PCB resistance, control circuitry, and other system losses.
Engineering tool
MOSFET Efficiency Calculator
Combine conduction, switching, and gate-drive loss to estimate MOSFET-stage efficiency and heat load.
Measured or expected system input power.
Power delivered by the modeled power stage.
RMS or representative on-state current.
Use the worst-case hot value at the applied VGS.
Fraction of the cycle with conduction loss.
Voltage involved in switching overlap.
Effective turn-on overlap time.
Effective turn-off overlap time.
Switching cycles per second.
Datasheet charge at relevant operating conditions.
Gate voltage swing delivered by the driver.
Result console
- Estimated efficiency
- 97.134531%
- Total MOSFET loss
- 2.95W
- Loss percentage
- 2.865469%
- Heat load
- 2.95W
Loss Breakdown
Conduction loss
0.5 W
Switching loss
2.4 W
Gate-drive loss
50 mW
Efficiency status
Good
The modeled MOSFET efficiency is suitable for many power stages. Compare conduction and switching loss to target the most effective optimization. The entered Pin is reasonably consistent with Pout plus the modeled MOSFET losses.
Formula reference
MOSFET Efficiency Formulas
All inputs are converted to SI units. Switching loss uses a first-order triangular overlap model, and efficiency uses output power plus modeled MOSFET losses.
Conduction loss: Pcond = ID² × RDS(on) × DutyTurn-on energy: Eon = 0.5 × VDS × ID × trTurn-off energy: Eoff = 0.5 × VDS × ID × tfSwitching loss: Pswitch = (Eon + Eoff) × fswGate-drive loss: Pgate = Qg × VGS × fswTotal loss: Ploss = Pcond + Pswitch + PgateEfficiency: η = Pout / (Pout + Ploss) × 100%Loss percentage = Ploss / (Pout + Ploss) × 100%Variable definitions
- ID
- drain current
- RDS(on)
- on-state resistance
- tr and tf
- switching overlap times
- Qg
- total gate charge
- Pout
- output power
- Ploss
- modeled MOSFET loss and heat load
Worked Example
Pout = 100 W, ID = 10 A, RDS(on) = 10 mΩ, duty = 50%, VDS = 48 V, tr = tf = 50 ns, fsw = 100 kHz, Qg = 50 nC, and VGS = 10 V.
Pcond = 10² × 0.01 × 0.5 = 0.5 W
Pswitch = [0.5 × 48 × 10 × (50 ns + 50 ns)] × 100 kHz = 2.4 W
Pgate = 50 nC × 10 V × 100 kHz = 0.05 W
Ploss = 2.95 W; η = 100 / 102.95 × 100% ≈ 97.13%; loss percentage ≈ 2.87%.
Engineering Notes
Output and loss
Efficiency depends on both useful output power and the modeled MOSFET losses.
High current
Conduction loss often dominates at high current because it increases with current squared.
High frequency or voltage
Switching loss often dominates at high switching frequency, high VDS, or long transition times.
Gate-drive demand
Gate-drive loss grows linearly with total gate charge, drive voltage, and switching frequency.
System boundary
Complete system efficiency also includes inductor, diode, driver, PCB, capacitor, magnetic, and control losses.
Support reference
FAQ
How do you calculate MOSFET efficiency?
Estimate conduction, switching, and gate-drive loss, add them to output power to obtain modeled input power, then calculate efficiency as Pout / (Pout + Ploss) × 100%.
What MOSFET loss affects efficiency most?
The dominant loss depends on operating conditions. Conduction loss often dominates at high current, while switching loss can dominate at high voltage, frequency, or transition time.
Why does switching frequency reduce efficiency?
Turn-on and turn-off energy is dissipated every switching cycle. Increasing frequency repeats that energy loss more often and also increases gate-drive power.
Does lower RDS(on) always improve efficiency?
Lower RDS(on) reduces conduction loss, but devices optimized for very low resistance may have higher gate charge or capacitance. The best choice balances conduction, switching, drive, cost, and thermal requirements.
Is gate drive power included in efficiency?
Yes. This model includes Qg × VGS × fsw as gate-drive loss. Driver quiescent current and other controller losses are outside the MOSFET-only estimate.
Documentation
Related Engineering Guides
Design notes, guides, and engineering articles linked to this tool.
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