MOSFET Conduction Loss Calculator
Estimate MOSFET conduction loss using drain current, on-state resistance, PWM duty cycle, hot resistance multiplier, and the number of parallel devices.
The tool reports effective hot RDS(on), ideal current sharing, per-device RMS current, and both per-device and total conduction loss for preliminary power-stage design.
Engineering tool
MOSFET Conduction Loss Calculator
Estimate hot RDS(on), per-device RMS current, and MOSFET conduction loss with duty cycle and parallel-device sharing.
Total on-state current shared by the parallel MOSFETs.
Datasheet on-resistance at the selected gate voltage and reference temperature.
Fraction of each cycle during which the MOSFET conducts.
Multiplier taken from normalized RDS(on) versus temperature data.
Ideal equal-current-sharing device count; enter a whole number.
Result console
- Effective hot RDS(on)
- 15mΩ
- Current per MOSFET
- 10A
- RMS current per MOSFET
- 7.071068A
- Conduction loss per MOSFET
- 0.75W
- Total conduction loss
- 0.75W
Engineering recommendation
Low Calculated Loss
The calculated conduction loss is relatively low, but still verify hot RDS(on), current sharing, switching loss, package thermal resistance, and junction temperature.
Formula reference
MOSFET Conduction Loss Formulas
The calculation treats the entered current as the on-state current and assumes equal sharing between parallel MOSFETs.
Current per MOSFET: Idevice = Id / NHot on-resistance: Rhot = RDS(on) × temperature multiplierRMS current per MOSFET: Irms = Idevice × √DPer-device loss: Pdevice = Idevice² × Rhot × DTotal conduction loss: Ptotal = Pdevice × NVariable definitions
- Id
- total on-state drain current
- N
- number of ideally sharing parallel MOSFETs
- D
- duty-cycle ratio from 0 to 1
- Rhot
- temperature-adjusted on-resistance
Worked Example
Id = 10 A, RDS(on) = 10 mΩ, duty cycle = 50%, temperature multiplier = 1.5, and one MOSFET.
Rhot = 10 mΩ × 1.5 = 15 mΩ
Irms = 10 × √0.5 ≈ 7.071 A
Pdevice = 10² × 0.015 × 0.5 = 0.75 W
Ptotal = 0.75 × 1 = 0.75 W
Engineering Notes
Current-squared loss
MOSFET conduction loss depends on the square of drain current.
Hot resistance
RDS(on) increases with junction temperature and should be adjusted for worst-case operation.
Gate-drive dependence
Datasheet RDS(on) depends on gate-source voltage as well as temperature.
Parallel layout
Parallel MOSFETs can reduce loss, but require symmetric source, drain, gate, and thermal layout.
Use RMS current
RMS current should be used for pulsed, PWM, or time-varying conduction waveforms.
Support reference
FAQ
How do you calculate MOSFET conduction loss?
Use the RMS drain current and hot on-resistance: Pcond = Irms² × RDS(on). For an on-state current with PWM duty cycle D, Irms = Id × √D.
Why does RDS(on) increase when hot?
The channel resistance of a silicon power MOSFET normally has a positive temperature coefficient. Use the datasheet normalized RDS(on) curve to estimate the multiplier at the expected junction temperature.
Why does current have a squared effect?
Resistive loss follows P = I²R. Doubling current while resistance remains constant therefore increases conduction loss by a factor of four.
Does duty cycle reduce conduction loss?
Yes. If current is present only during part of each cycle, average conduction loss scales with duty cycle. The calculation assumes the entered current is the on-state current.
Can I reduce loss by paralleling MOSFETs?
Ideal parallel MOSFETs divide current and reduce total conduction loss, but real sharing depends on symmetric PCB resistance, gate drive, thermal coupling, and device variation.
Documentation
Related Engineering Guides
Design notes, guides, and engineering articles linked to this tool.
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