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An IGBT combines a MOSFET gate with a bipolar output, so unlike a MOSFET it has a roughly fixed on-state voltage VCE(sat) instead of a resistance. Its total loss is conduction loss (VCE(sat)×IC, scaled by duty) plus switching loss, which datasheets give directly as switching energies Eon and Eoff in millijoules.
| Loss | Formula | Notes |
|---|---|---|
| Conduction | VCE(sat) × IC × D | fixed drop × current |
| Switching | (Eon+Eoff) × fsw | from datasheet energies |
| Junction temp | TA + Ptotal × θJA | use heat-sink temp for TA |
Because switching energy scales with bus voltage and current, use the second tab to adjust datasheet numbers to your actual operating point before computing Psw.
Conduction loss while the device is on (VCE(sat)×IC, scaled by duty cycle) and switching loss during turn-on and turn-off, given by the datasheet energies Eon and Eoff.
The collector-emitter voltage when the IGBT is fully on — typically 1.5–2.5 V. Unlike a MOSFET's resistance, it is roughly constant, so conduction loss is VCE(sat)×IC.
The energy dissipated during a single turn-on and turn-off event, in millijoules, from the datasheet at a stated test voltage and current. Multiply their sum by frequency to get switching loss.
IGBTs have a current "tail" at turn-off that adds significant Eoff. This makes their switching loss high, which is why they are usually run below ~20 kHz.
Eon/Eoff are quoted at specific test conditions. Switching energy scales roughly linearly with bus voltage and current, so adjust to your actual operating point (second tab) for a realistic estimate.
MOSFETs win at lower voltage, lower current, and higher frequency (resistive loss falls with current). IGBTs win at high voltage and high current where a fixed ~2 V drop beats I²R.
Most silicon IGBTs are rated to 150 °C or 175 °C. Design for a healthy margin (e.g. keep TJ below ~125 °C) for reliability.
For a module on a heat sink, use the heat-sink (case) temperature with θJC. If you only have θJA, use ambient. This calculator lets you enter whichever pair matches your data.
Lower VCE(sat) for conduction loss, reduce switching frequency or use faster/soft-switching for switching loss, and improve cooling to keep the junction temperature down.
Yes — in inductive-load bridges each IGBT needs a freewheeling diode. That diode has its own conduction and reverse-recovery loss, which a full design must also include.
Commonly 2–20 kHz. Above that, switching loss usually makes MOSFETs or wide-bandgap (SiC) devices a better choice.
It captures the two dominant loss mechanisms and is excellent for device and heat-sink selection. Full designs also include diode loss, temperature-dependent parameters, and the actual current waveform.
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