MOSFET Switching Loss Calculator
Estimate MOSFET turn-on energy, turn-off energy, total energy per cycle, and average switching power from drain voltage, current, transition times, and switching frequency.
This first-order overlap model supports early power-stage and thermal design before waveform measurements or detailed device simulation are available.
Engineering tool
MOSFET Switching Loss Calculator
Estimate turn-on and turn-off energy, switching power, and heat load from voltage-current overlap.
Voltage across the MOSFET immediately before the transition.
Load current during the switching transition.
Effective turn-on voltage-current overlap duration.
Effective turn-off voltage-current overlap duration.
Number of complete switching cycles per second.
Correction factor for nonideal overlap; use 1 for the triangular estimate.
Result console
- Turn-on switching energy (Eon)
- 12µJ
- Turn-off switching energy (Eoff)
- 12µJ
- Total switching energy per cycle
- 24µJ
- Switching power loss
- 2.4W
- Estimated heat load
- 2.4W
Engineering recommendation
Thermal Verification Required
Include this switching loss with conduction, gate-drive, reverse-recovery, and leakage losses, then verify package and PCB junction temperature at worst-case conditions.
Formula reference
MOSFET Switching Loss Formulas
The equations approximate hard-switching overlap. Reverse recovery, output capacitance, gate-drive loss, ringing, and nonlinear waveforms require separate analysis.
Turn-on energy: Eon = 0.5 × VDS × ID × tr × factorTurn-off energy: Eoff = 0.5 × VDS × ID × tf × factorTotal energy per cycle: Etotal = Eon + EoffSwitching power: Pswitching = Etotal × fswVariable definitions
- VDS
- drain-source voltage during the transition
- ID
- drain current during the switching event
- tr and tf
- effective voltage-current overlap times
- factor
- correction applied to the ideal triangular overlap
Worked Example
VDS = 48 V, ID = 10 A, tr = 50 ns, tf = 50 ns, fsw = 100 kHz, and overlap factor = 1.
Eon = 0.5 × 48 × 10 × 50 ns = 12 µJ
Eoff = 0.5 × 48 × 10 × 50 ns = 12 µJ
Etotal = 12 + 12 = 24 µJ per cycle
Pswitching = 24 µJ × 100 kHz = 2.4 W
Engineering Notes
Frequency scaling
Switching loss increases linearly with switching frequency.
Voltage and current
Switching energy increases with both drain voltage and drain current.
Speed and EMI
Faster switching reduces overlap loss but can increase EMI, ringing, and overshoot.
Datasheet conditions
Datasheet switching energy depends on gate resistance, driver voltage, load, and test layout.
Hard-switching limits
Hard-switching loss can dominate total device loss at high voltage or high frequency.
Support reference
FAQ
How do you calculate MOSFET switching loss?
Estimate turn-on and turn-off energy from the voltage-current overlap during each transition, add the energies, and multiply by switching frequency: Psw = (Eon + Eoff) × fsw.
What is turn-on energy?
Turn-on energy is the energy dissipated while drain current rises and drain-source voltage falls. The triangular overlap estimate is Eon = 0.5 × VDS × ID × tr.
What is turn-off energy?
Turn-off energy is the energy dissipated while drain current falls and drain-source voltage rises. It is estimated from the turn-off overlap duration tf.
Why does switching frequency increase loss?
Each cycle dissipates switching energy. Increasing the number of cycles per second raises average switching power in direct proportion to frequency.
How can MOSFET switching loss be reduced?
Use an appropriate gate driver and gate resistance, reduce transition time where EMI allows, choose a lower-charge device, optimize layout and snubbing, reduce frequency, or use a soft-switching topology.
Documentation
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Design notes, guides, and engineering articles linked to this tool.
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