An IGBT, or Insulated Gate Bipolar Transistor, is a power semiconductor switch that combines the best traits of two older transistor types into one device. It uses a voltage-controlled input (like a MOSFET) paired with a high-power output stage (like a bipolar transistor), letting it handle both high voltage and high current with relatively simple control signals. IGBTs are the workhorse behind electric vehicle inverters, solar power systems, industrial motor drives, and many other applications where large amounts of electrical power need to be switched efficiently.
How an IGBT Works
To understand the IGBT, it helps to know the two devices it descends from. A MOSFET is easy to control because you just apply a small voltage to its gate terminal, but it struggles with high voltages. A bipolar junction transistor (BJT) handles high voltages well, but it requires a large continuous current to keep it switched on, which wastes energy and complicates the control circuit.
The IGBT solves this by using a MOSFET structure at the input and a bipolar structure at the output. You control it with a small voltage signal at the gate, just like a MOSFET, so it draws almost no power from the control circuit. But internally, the bipolar output stage lets current flow through the device at voltages that would overwhelm a standard MOSFET. The result is a switch that’s easy to drive and capable of handling serious power.
Like a MOSFET, the IGBT is a voltage-controlled device. Its three terminals are called the gate, collector, and emitter. Applying a voltage to the gate turns the device on, allowing current to flow from collector to emitter. Remove the gate voltage and current stops. This on/off switching, repeated thousands of times per second, is what allows IGBTs to convert and regulate electrical power.
How IGBTs Compare to MOSFETs and BJTs
The three transistor types each occupy a different sweet spot in power electronics. MOSFETs can switch extremely fast, up to 500 kHz, and carry hundreds of amps, but they’re typically limited to voltages well under 100 V. BJTs can block several hundred to over a thousand volts, but their need for large base drive currents limits practical switching speeds to around 100 kHz, and they’re lower current devices overall.
IGBTs were developed specifically to fill the gap. Modern high-power IGBTs can handle currents above 1,000 A while switching several thousand volts. The tradeoff is speed: practical switching frequencies for high-power IGBT designs rarely exceed 50 kHz. Manufacturers have nearly tripled IGBT switching speeds since the devices were first commercialized in the 1980s, but they still can’t match MOSFETs for rapid switching. This makes IGBTs ideal for applications where raw power matters more than switching frequency.
Voltage and Current Ratings
Commercially available IGBTs span a wide range of ratings. At the lower end, 600 V and 650 V devices handle currents up to 600 A. Mid-range modules rated at 1,200 V to 1,700 V can carry up to 3,600 A. For heavy industrial and grid-scale applications, devices rated at 3,300 V handle up to 1,500 A, 4,500 V devices handle 1,200 A, and 6,500 V devices handle 750 A. Devices rated above 10,000 V are still in the testing phase.
The general pattern: as voltage ratings go up, maximum current comes down. Designers choose the rating that fits their application’s specific voltage and current requirements, balancing power handling against cost and thermal constraints.
Where IGBTs Are Used
You’ll find IGBTs in nearly every system that needs to convert or control large amounts of electrical power. Electric vehicles rely on IGBT-based inverters to convert battery DC power into the AC power that drives the motors. Solar power systems use 1,200 V IGBT modules to convert the DC output of photovoltaic panels into grid-compatible AC electricity. Energy storage systems use similar modules to manage the flow of power in and out of battery banks.
Industrial motor drives are another major application. Variable-frequency drives, which control the speed of large motors in factories, elevators, and HVAC systems, depend on IGBTs to rapidly switch power at precise intervals. Train and subway propulsion systems, wind turbines, and uninterruptible power supplies all use IGBTs as their core switching element. The technology is particularly important for any system where blocking voltages exceed 600 V, which covers most grid-connected and high-power equipment.
Energy Loss and Heat
No switch is perfect, and IGBTs lose some energy as heat every time they operate. The two main sources of loss are conduction loss and switching loss. Conduction loss occurs while the IGBT is turned on and current is flowing through it. The device has a small internal resistance, so some energy is converted to heat, similar to how a wire gets warm when carrying current. Switching loss occurs during the brief transition periods when the IGBT turns on or off. During these transitions, voltage and current overlap momentarily, generating a burst of wasted energy.
Both types of loss increase as the device gets hotter, creating a feedback loop: losses generate heat, and heat increases losses. This is why thermal management, typically through heatsinks, fans, or liquid cooling, is critical in IGBT-based systems. Keeping the internal junction temperature within safe limits directly affects how long the device lasts and how efficiently it operates.
Driving and Protecting an IGBT
Although IGBTs are voltage-controlled and relatively simple to switch on and off, the gate driver circuit that controls them needs to include several layers of protection. The most common concern is a short circuit, where the IGBT suddenly has to carry far more current than intended. Gate drivers detect this by monitoring the voltage across the device. When that voltage rises above a threshold (indicating the IGBT is no longer in its normal operating region), the protection circuit kicks in.
Rather than shutting the device off instantly, which could cause dangerous voltage spikes, most protection systems use a “soft turn-off” approach. This gradually reduces the gate voltage using a small, controlled current, giving the magnetic components in the circuit time to absorb the energy safely. Some systems use a two-stage approach, first pulling the gate down to an intermediate voltage and pausing briefly before completing the turn-off. These techniques prevent damage to both the IGBT and the surrounding circuit.
Silicon Carbide as an Alternative
Silicon carbide (SiC) MOSFETs have emerged as a competitor to traditional silicon-based IGBTs, especially in applications where efficiency and size matter. SiC devices can switch faster and produce less heat, which means smaller heatsinks, smaller filtering components, and a more compact overall system. In wind turbine converters, for example, SiC-based designs have demonstrated meaningful reductions in the volume of passive components like capacitors and inductors compared to equivalent IGBT designs.
The catch is cost. SiC devices remain significantly more expensive than silicon IGBTs, and for many high-power applications, especially those operating at moderate switching frequencies, IGBTs still offer the best balance of performance, reliability, and price. The two technologies will likely coexist for years, with SiC gaining ground in applications where efficiency gains justify the premium and IGBTs continuing to dominate in cost-sensitive, high-power systems.