MOSFET vs IGBT: Structure, Switching Behavior, and How to Choose

Quick answer

A silicon power MOSFET is usually the first device to evaluate when switching frequency is high, bus voltage is low or moderate, and low-current efficiency matters. An IGBT is often competitive when blocking voltage and current are high, switching frequency is moderate, and its lower high-current conduction drop offsets its turn-off energy. At higher bus voltages, a SiC MOSFET can move the crossover again by combining high-voltage blocking with fast switching.

There is no reliable universal cutoff such as "below this voltage use a MOSFET" or "above this current use an IGBT." Select candidate parts with adequate voltage and current margin, then compare hot-condition conduction loss, switching energy, diode behavior, gate-drive requirements, fault response, package thermal performance, and system cost. The device with the lowest headline resistance or saturation voltage is not necessarily the device with the lowest converter loss.

MOSFET vs. IGBT: Core Differences

These are device-family tendencies, not guaranteed crossover points. Toshiba's comparison shows that the MOSFET can have the lower on-voltage at low current while the IGBT can cross below it at higher current, and that the result changes with temperature.^[1] The comparison must therefore use real candidate parts at the intended operating point.

Why MOSFET and IGBT Behavior Differs

Both devices use an insulated gate, so neither requires continuous gate current in the way a bipolar transistor requires base drive. The gate driver still has to charge and discharge capacitance during every switching event, but the steady-state control interface is voltage driven.

A power MOSFET and an IGBT share a MOS-gated input, but the IGBT adds collector-side carrier injection.

Power MOSFET: majority-carrier switching

In an n-channel power MOSFET, gate voltage creates a channel that connects the source region to the drift region. Electrons carry the current, so there is no stored minority charge in the drift region to remove at turn-off. This is the physical reason a MOSFET can switch quickly.

The drift region supports the off-state voltage. In a silicon MOSFET, raising the voltage rating generally requires a thicker, more lightly doped drift region, increasing its contribution to RDS(on). Superjunction structures improve this tradeoff, but they do not remove the need to compare on-resistance, capacitance, switching energy, and body-diode behavior for the exact part.

IGBT: conductivity modulation

An IGBT adds a p-type collector-side layer that injects holes into the drift region. The resulting electron and hole population increases drift-region conductivity. This conductivity modulation makes high-voltage, high-current conduction attractive, but the stored charge must recombine or be removed when the device turns off.^[1]

The remaining current during turn-off is the IGBT tail current. It overlaps with collector-emitter voltage and adds energy loss. Modern field-stop and trench IGBTs have improved this behavior, but the data-sheet Eoff curve, not a generic statement about IGBTs, determines the actual penalty.

How to Compare MOSFET and IGBT Power Loss

Start with the current waveform and the fraction of the switching period for which each device conducts. Perform the comparison at the expected hot junction temperature. Room-temperature headline values can understate loss, especially when a MOSFET's on-resistance rises substantially with temperature.

MOSFET conduction loss

If IRMS,device is the RMS current through the MOSFET over the complete switching period, a first-pass estimate is:

Pcond,MOSFET approximately equals IRMS,device2 x RDS(on)(TJ)

Use the data-sheet temperature relationship or normalized curve to estimate hot RDS(on). Include package and interconnect resistance when they are material. If the RMS current is calculated only during the conduction interval, the duty factor must be handled consistently.

IGBT conduction loss

An IGBT is not accurately represented by one resistance. A coarse screening estimate is:

Pcond,IGBT approximately equals VCE(sat)(I,TJ) x Iavg,device

For a better result, integrate the data-sheet on-state voltage curve over the actual current waveform. The Renesas loss note uses the same separation between conduction loss and switching loss and emphasizes that the selected voltage and current terms must match the application waveform.^[3]

Switching loss

When the data sheet provides switching-energy curves under relevant conditions, average switching loss can be estimated as:

Psw approximately equals fs x (Eon + Eoff)

Switching energy depends on bus voltage, current, junction temperature, gate resistance, gate voltage, commutation inductance, and the diode used in the test circuit. Do not copy an Eon or Eoff value into a different operating point without using the manufacturer's curves or calculation tool. For IGBTs, Eoff includes tail-current energy; Eon can also include diode reverse-recovery interaction.^[3]

The IGBT's stored charge produces a turn-off tail that adds switching energy.

Losses that should not be omitted

• Gate-drive loss: a useful driver-supply estimate is Pgate approximately equals Qg x Vdrive x fs per switch.

• Output-capacitance loss: check Eoss or the manufacturer's nonlinear capacitance model, particularly in hard-switched MOSFET stages.

• Reverse-recovery loss: include the MOSFET body diode or the IGBT's antiparallel diode under the actual commutation conditions.

• Dead-time loss: reverse current can flow through a diode or third-quadrant channel during dead time.

• Parasitic and snubber loss: ringing control, stray inductance, and clamp networks can materially change total dissipation.

The final thermal check is TJ, not efficiency alone. Combine total semiconductor loss with the package, interface, heatsink or cold plate, PCB copper, coolant or airflow, and worst-case ambient or coolant temperature.

Reverse Conduction and Freewheeling

A silicon power MOSFET contains an intrinsic body diode. That does not make every MOSFET body diode an ideal freewheeling element. Its forward drop, reverse-recovery charge, recovery time, recovered energy, and dynamic ruggedness must match the topology. ST's body-diode application note shows why reverse recovery can add current stress and loss in bridge converters.^[5]

During synchronous operation, reverse current may flow through the MOSFET channel after the device is turned on, reducing the time spent in the diode. Dead time, control timing, and third-quadrant characteristics therefore affect both loss and reliability.

A standard IGBT does not have the same intrinsic body-diode path. Bridge and inverter applications normally use an antiparallel diode, either as a separate device or co-packaged in an IGBT/module. Its current rating, forward drop, reverse recovery, temperature range, and switching match are part of the switch selection. A part number that omits the diode cannot be substituted for a co-packaged version without reviewing the complete commutation path.

Application Starting Points

Toshiba presents MOSFETs as the higher-frequency option and IGBTs as a common high-output-power option, while also showing an overlap region where either may be used.^[2] Treat this as a starting map, not a substitute for a loss calculation.

Eight-Step MOSFET vs. IGBT Selection Workflow

1. Define the topology and waveforms. Record DC-link range, hard- or soft-switching behavior, switching frequency, duty cycle, dead time, RMS current, peak current, overload profile, and reverse-current intervals.

2. Set voltage margin from real transients. Select blocking voltage from the maximum steady bus plus overshoot and abnormal events. Do not use nominal bus voltage as the device rating.

3. Screen current and safe operating area. Check continuous current only after reviewing pulsed current, current density, SOA, repetitive avalanche where applicable, and package terminal limits.

4. Calculate hot conduction loss. Use MOSFET RDS(on) at temperature or the IGBT VCE(sat) curve at current and temperature. Compare across the actual load profile, not only at rated power.

5. Calculate switching and commutation loss. Scale Eon, Eoff, output-capacitance energy, and diode recovery using manufacturer curves or tools that match voltage, current, gate resistance, and temperature.

6. Design the gate drive and layout together. Verify gate voltage limits, source and sink current, Miller immunity, isolation, common-mode transient immunity, negative turn-off requirements, gate resistance, loop inductance, and acceptable dv/dt and di/dt.

7. Check fault behavior. Confirm short-circuit withstand time if the application requires it, plus DESAT or overcurrent detection delay, soft turn-off, shoot-through prevention, and the energy absorbed during a fault. Never assume every IGBT or SiC MOSFET has the same short-circuit capability.

8. Close the thermal and economic model. Calculate junction temperature over worst-case load and ambient conditions, then compare package, heatsink or cold plate, gate driver, diode, snubber, EMI filter, magnetics, assembly, qualification, availability, and lifecycle cost.

Voltage, current, frequency, thermal limits, reverse conduction, protection, and system cost all affect the final choice.

How SiC Changes the MOSFET vs. IGBT Decision

A SiC MOSFET is a majority-carrier device, so it can switch quickly without IGBT tail current while supporting high blocking voltage. This makes SiC a serious candidate in voltage classes and power levels that were historically served by silicon IGBTs. Infineon identifies EV traction, solar, and industrial motor drive among the applications served by high-voltage SiC MOSFETs.^[6]

SiC is not an automatic upgrade. Its faster edges can increase ringing, common-mode current, insulation stress, and EMI. Layout inductance and driver common-mode immunity become more important, and the protection circuit may need to react faster than an IGBT-oriented design. Compare system-level gains such as lower switching loss, smaller magnetics, reduced cooling, or a higher switching frequency against device, driver, EMI, and manufacturing cost.

GaN devices also extend high-frequency switching, especially in lower- and medium-power conversion, but their voltage classes, reverse-conduction behavior, packaging, drive requirements, and application space differ from both SiC MOSFETs and IGBTs. They should be evaluated as a separate technology rather than treated as a generic MOSFET replacement.

Frequently Asked Questions

Which is better, a MOSFET or an IGBT?

Neither is universally better. A silicon MOSFET often has the advantage at high switching frequency and low current, while an IGBT may have lower conduction loss at high voltage and high current. A SiC MOSFET can compete with the IGBT in many high-voltage applications. Calculate total loss and junction temperature for actual candidate parts.

Is there a fixed voltage where I should change from a MOSFET to an IGBT?

No. Voltage rating changes the available device technologies, but the crossover also depends on current, switching frequency, temperature, topology, reverse recovery, package, and cost. Use voltage as a screening constraint, not as the final decision.

Why can an IGBT be more efficient at high current?

Minority-carrier injection produces conductivity modulation in the IGBT drift region. At high voltage and current, this can produce a lower conduction drop than a comparable silicon MOSFET. The benefit must be weighed against turn-on and turn-off energy, including tail-current loss.

Why does a MOSFET normally switch faster?

A MOSFET is a majority-carrier device and does not store minority charge in the drift region. It still has gate charge and nonlinear capacitances, so switching is not lossless, but it avoids the IGBT's minority-carrier tail.

Can I use a MOSFET body diode as the freewheeling diode?

Only after checking the exact device and topology. Review forward drop, reverse-recovery charge, recovery energy, dead time, current, temperature, and dynamic ruggedness. Some hard-switched bridges benefit from a fast-recovery MOSFET technology, SiC MOSFET, or a separate diode strategy.

Does every IGBT include an antiparallel diode?

No. Many IGBTs and modules are sold with a co-packaged diode, while others are not. Confirm the circuit symbol, ordering code, and diode specifications in the data sheet.

Can a SiC MOSFET directly replace an IGBT?

Do not assume a drop-in replacement. Voltage class, current, package pinout, gate voltage, driver strength, negative turn-off, short-circuit protection, switching speed, EMI, isolation stress, cooling, and control timing may all require redesign and validation.

Conclusion

The practical MOSFET-versus-IGBT decision is a total-loss and system-design exercise. A MOSFET rewards higher frequency and low-current operation; an IGBT can reward high-voltage, high-current conduction; and a SiC MOSFET can move the high-voltage boundary toward faster switching. Build a short list from voltage, current, topology, and fault requirements, then compare conduction, switching, diode, drive, and thermal performance at the real operating conditions.

Manufacturer data sheets, loss curves, SPICE models, evaluation hardware, and thermal measurements remain the final authority. Family-level rules are useful for screening, but they cannot prove that one specific part is safe, efficient, or interchangeable with another.

Sources and References

1. Toshiba Electronic Devices and Storage: What is the difference between MOSFETs and IGBTs? Device structure, conductivity modulation, tail current, and conduction crossover.

2. Toshiba Electronic Devices and Storage: For what applications should MOSFETs and IGBTs be used? General power and switching-frequency application map.

3. Renesas: IGBT Loss Calculation Conduction, switching, diode, and inverter loss calculations.

4. Texas Instruments: Power Loss in Switching Power Supplies Conduction, switching, dead-time, and reverse-recovery loss mechanisms.

5. STMicroelectronics AN2626: MOSFET Body Diode Recovery Body-diode conduction and reverse-recovery behavior.

6. Infineon: What is a SiC MOSFET? High-voltage SiC applications and design considerations.