Semiconductors
Model class: Datasheet-driven estimate
MOSFET total-loss and temperature estimate
Estimate MOSFET conduction and switching loss, identify the dominant term, and form a first-pass junction-temperature estimate.
Interactive engine
Start with the stated conditions.
Values stay in this browser. Choose a representative scenario, then calculate deliberately.
Example ready
Calculate to inspect the result.
The result will identify the direct answer, assumptions, and any warning that changes the next decision.
Assumptions to check
- RDS(on) and switching energy match the actual conditions.
- Loss terms are independent first-pass estimates.
- The thermal metric matches its temperature reference.
Keep data-sheet conditions attached
MOSFET loss is the sum of several mechanisms, and each data-sheet value has conditions. This engine combines a duty-weighted RMS conduction estimate with entered switching energy times frequency, then applies a stated thermal path.
The result identifies the larger term. That is useful for deciding whether lower resistance, lower switching energy, lower frequency, stronger drive, or a different topology is most likely to matter.
Temperature is a feedback path
RDS(on) usually rises with junction temperature, and thermal resistance depends on the package, board, airflow, and reference definition. Treat this as a screening estimate, then compare a selected part at matched conditions and validate the real switching waveform.
Use the loss split to choose the next improvement
Conduction loss is proportional to current squared, on-resistance, and duty cycle, while the entered switching energy rises directly with switching frequency. That contrast helps identify a useful next experiment. If conduction loss dominates, check the hot RDS(on), current waveform, package, and parallel-current sharing. If switching loss dominates, check gate drive, voltage and current overlap, switching frequency, layout inductance, and the data-sheet test circuit behind the energy number.
The temperature result is intentionally one-way. A real MOSFET warms, RDS(on) changes, switching energy can change, and the board thermal path may differ greatly from a reference layout. Use maximum input, output, frequency, ambient, and tolerance corners for screening. Then use the selected device’s safe-operating-area information, thermal data, waveform measurement, and a board-aware thermal check before treating the result as a reliable operating limit. Record which input corner produced the worst estimated loss.
Common mistakes
- Mixing switching-energy conditions.
- Using room-temperature RDS(on) at a hot junction.
- Treating RθJA as a portable package property.
Model limit and handoff
Use the selected MOSFET data sheet, thermal model, switching waveform, and SOA limits before a critical decision.
FAQs
Why is switching loss so large?
At high frequency, even small energy per event is multiplied by many events per second.