IGBT vs MOSFET: How IGBTs Work and How to Select Them

Choosing between an IGBT and a MOSFET starts with the converter’s current and switching events. An insulated gate bipolar transistor combines a voltage-controlled insulated gate with bipolar conduction in its power path. It can be useful in power converters and motor drives, but its turn-off behavior, gate drive and associated diode must fit the circuit. An IGBT vs MOSFET comparison based only on voltage class misses those operating details.

Read the three terminals and the complete circuit symbol

An ordinary IGBT has gate, collector and emitter terminals. The driver controls gate-to-emitter voltage; load current flows through the collector–emitter path in the supported direction. The gate draws transient current when its capacitances charge or discharge, even though the insulated gate does not need continuous base current like a conventional bipolar transistor.

Check the exact pinout, including any Kelvin emitter terminal or exposed metal connection. A package drawing tells you physical connections; a circuit symbol tells you whether a diode is included. Many converter applications need a reverse-current path, but that path is not an inherent MOSFET-style body diode in a conventional IGBT. It may be provided by a co-packaged diode, a reverse-conducting product architecture or a separate device.

That distinction matters in an inverter leg where current can reverse while the commanded output voltage has another polarity. Establish the entire current path before comparing headline transistor ratings. Infineon’s discrete IGBT datasheet explanation is a useful primary reference for reading the terminal and parameter information.

Understand conduction and the turn-off tail

Carrier injection in an IGBT’s power structure can reduce on-state voltage for its intended operating range. Stored carriers also have to be removed during turn-off. The resulting current tail can contribute to turn-off energy while significant collector–emitter voltage is present. Its size depends on device construction and the electrical and thermal conditions; it is not a fixed penalty shared by every IGBT.

A power MOSFET is normally assessed for on-state loss using its supported drain–source resistance at the actual gate voltage and temperature. An IGBT is normally assessed using its collector–emitter saturation characteristic at the relevant current and gate conditions. Treating the IGBT’s on-state path as a single room-temperature resistance obscures the comparison.

The Infineon IGBT characterization note explains the connection between device characteristics and switching behavior. These mechanisms suggest what to compare; they do not provide a universal crossover voltage, current or switching frequency.

Compare IGBT vs MOSFET at the same operating point

Use the same bus voltage, current waveform, junction temperature, switching frequency and topology. Define the gate conditions for each candidate rather than giving both an arbitrary drive that suits only one. Include the diode or reverse-conduction path and any differences in commutation. Otherwise, a comparison can favor a part simply because one loss term has been left out.

An IGBT can be attractive where its conduction characteristic and permitted switching duty meet the design’s thermal budget. A MOSFET may offer a different balance of conduction, switching and control behavior. Silicon carbide MOSFETs introduce another set of electrical and drive considerations. Circuit architecture, cooling and cost all influence the final result.

Comparison item	IGBT assessment	MOSFET assessment
On-state loss	VCE versus current, gate drive and temperature	RDS(on) versus gate drive and temperature
Switching loss	Turn-on and turn-off energy under matching conditions	Switching overlap, output charge and commutation effects
Reverse current	Identify included or external diode path	Evaluate body diode or controlled reverse conduction
Fault operation	Supported short-circuit and safe operating conditions	Supported SOA, pulse and avalanche conditions

Calculate a first loss budget without overclaiming

For a simplified example, assume an IGBT carries a constant 20 A for half of each switching cycle at an on-state voltage of 1.7 V. Approximate conduction loss is 1.7 × 20 × 0.5 = 17 W. Assume its combined turn-on and turn-off energy is 1.2 mJ at the relevant conditions, with one turn-on and one turn-off per cycle. At 20 kHz, switching loss is 0.0012 × 20,000 = 24 W, giving a 41 W subtotal.

At 5 kHz with those same assumed event energies and conduction duty, switching loss would be 6 W and the subtotal 23 W. These are illustrative inputs, not measured product performance. The estimate excludes the companion diode, driver supply, auxiliary circuits and any other relevant losses. Actual energy changes with voltage, current, temperature and switching conditions.

This example explains why changing frequency can alter the loss balance. It does not show that 5 kHz is better for the system: magnetic size, acoustic behavior, output quality and control requirements can change too. Compare a complete feasible converter, rather than optimizing one transistor in isolation.

Read switching-energy test conditions carefully

Turn-on and turn-off energy entries are linked to a test circuit and specified conditions. Collector current, voltage, gate resistance, gate supply and temperature all affect the result. The diode used in the switching test can influence turn-on energy. Comparing values from different test arrangements without adjustment can create a false ranking.

Typical curves help develop an estimate, but they are not a guaranteed maximum at every operating point. Keep any extrapolation explicit. If supported information does not cover a critical condition, obtain relevant manufacturer guidance or validate that condition in the actual design. Do not extend a curve beyond its shown domain merely to complete a spreadsheet.

For a PWM inverter, device current varies through the fundamental cycle. One constant-current point is a useful teaching calculation but an incomplete model of the operating duty. Integrate or sample the relevant conduction and switching states. Count events per device: system switching frequency alone does not identify how often every junction switches.

Design the driver around the selected IGBT

Gate drive must establish the supported on and off states, supply transient gate current and remain stable during switching. Gate threshold is not the voltage required for low-loss rated-current operation. Driver peak-current capability also does not mean that the same current flows throughout the complete transition. Gate charge, resistance and the surrounding inductance determine the waveform.

Use the device’s recommended gate conditions and absolute limits. Negative off-state bias, a Miller clamp or separate turn-on and turn-off resistances may be useful in particular designs, but none is a universal requirement for every IGBT. The Kelvin emitter, when provided and correctly routed, helps separate the gate return from the power-current path.

TI’s gate-driver fundamentals provides context for charge and driver behavior. For an introductory explanation of the stage itself, see the high-speed gate driver guide. Select the driver and switch as an interacting circuit, including startup and supply-failure states.

Coordinate fault detection and turn-off

Some IGBTs specify short-circuit withstand under particular gate voltage, bus voltage and starting temperature conditions. That information cannot be assumed for an unrelated part or treated as a repetitive operating allowance. Fault detection and current interruption must complete within a defensible window, including propagation delay, blanking and turn-off behavior.

Desaturation detection is one possible method. For example, the TI ISO5851 driver includes desaturation-related protection features. The feature name alone does not establish the complete protection time: the external network, thresholds and system design still matter. A very abrupt fault turn-off can create damaging voltage overshoot through loop inductance.

Record the current and voltage reached during the defined fault, the driver’s response and the switch’s stress. Include the diode path and stored energy elsewhere in the converter. Normal-load efficiency tests cannot substitute for fault-response evidence, and an acceptable gate waveform in steady operation cannot establish a safe startup sequence.

Evaluate the freewheel diode as part of the choice

In inductive loads, current needs a path when the commanded switch turns off. A co-packaged diode may simplify assembly, but its recovery, voltage drop and thermal interaction remain part of the design. Sharing a package can also couple the junction temperatures. Check how the datasheet defines the transistor and diode ratings and thermal paths.

During commutation, recovery current may increase the stress and energy in the opposite switch. A diode with different behavior can change ringing and electromagnetic interference. This is why substituting an IGBT with a seemingly better Eoff number can still worsen the complete leg if the associated diode or switching conditions differ.

The fast recovery diode guide explains the recovery quantities. For an IGBT comparison, bring those quantities back into the actual leg: dead time, load current direction, loop inductance and temperature determine which devices conduct and what happens when the next switch turns on.

Choose discrete packages or modules from the assembly needs

Discrete IGBTs give the designer control over placement, cooling and circuit arrangement. Modules can integrate multiple switches, diodes and connections in a coordinated package. Neither format has a universal power boundary at which it becomes mandatory. Assembly complexity, insulation, heat spreading, service requirements and the number of current paths can matter as much as output power.

Assess the complete heat path with the intended interface and mounting method. Transient thermal information is needed for changing load, not just a steady-state junction-to-case number. Consider current sharing and gate-loop differences if multiple devices operate in parallel. A positive temperature coefficient in part of an operating range does not establish balanced dynamic sharing by itself.

Check the actual mechanical envelope and terminal connections before sourcing an alternate. A module outline or discrete package name is not an electrical compatibility statement. Preserve mounting instructions and any approved interface materials with the design record.

Use sourcing evidence rather than market forecasts

An IGBT purchasing decision benefits from exact product status, ordering codes, qualification scope and documented alternates. Broad claims about a growing market do not establish availability of your chosen part or the suitability of a replacement. Infineon’s IGBT product portfolio is one primary place to inspect current offerings; distributor stock should be checked at the time of purchase.

Keep lifecycle information and manufacturer change notices with the approved bill of materials. Verify the supply channel and lot identification appropriate to the application. If the alternate changes die behavior, diode construction or package thermal performance, determine which validation results need reopening. Similar voltage and current ratings do not settle that question.

The useful final decision is a matched comparison: losses at the operating duty, gate and fault behavior, heat removal, mechanical compatibility and supported supply. That record makes an IGBT choice understandable and repeatable without relying on a universal frequency rule or an unsupported market prediction.

Continue through this engineering topic

For the complete selection, design, verification, and troubleshooting path, explore the MOSFET IGBT and Transistor Hub.

• Practical guide: High Voltage MOSFETs: Ratings, Losses and Circuit Design Checks
• Practical guide: Gate, Drain, Source: The Three Pins of a MOSFET Explained With a Water Analogy
• Practical guide: Transistors for Power and Signal Design: Types and Selection
• Ask Good-Ark technical support about this application