An IGBT (Insulated Gate Bipolar Transistor) is a power semiconductor switch that combines two older transistor technologies into one device, giving it the easy control of a MOSFET and the high-current muscle of a bipolar junction transistor (BJT). It has three terminals: a gate, a collector, and an emitter. You’ll find IGBTs inside electric vehicle inverters, solar power systems, industrial motor drives, and trains, essentially anywhere large amounts of electrical power need to be switched on and off efficiently.
How an IGBT Works
At its core, an IGBT is controlled by voltage, not current. When you apply a positive voltage to the gate terminal, electric charges build up between the insulated gate oxide layer and the semiconductor material beneath it. This creates what engineers call an “inverted channel,” a thin conductive path that allows current to flow from the collector to the emitter. The device is now “on.”
When the gate voltage drops to zero or goes negative, that channel disappears and current stops flowing. The IGBT is now “off.” This on/off switching is the fundamental job of the device, and it can happen thousands of times per second. The key advantage is that the gate draws almost no current itself. A tiny control signal can switch hundreds or even thousands of amps through the main circuit, which makes the IGBT extremely efficient to drive.
Internally, the IGBT pairs an N-channel MOSFET on the input side with a PNP bipolar transistor on the output side, connected in a Darlington-like configuration. The MOSFET handles the gate signal with high input impedance (meaning it barely loads the control circuit), while the bipolar transistor carries the heavy current with low voltage drop. This combination is what gives the IGBT its distinctive strengths.
Why IGBTs Exist Alongside MOSFETs
If MOSFETs already switch efficiently, why do IGBTs exist? The answer comes down to voltage and power levels. At higher voltages, a standalone MOSFET’s internal resistance climbs steeply, wasting more energy as heat. IGBTs sidestep this problem through something called conductivity modulation: the bipolar transistor portion floods the semiconductor with extra charge carriers, keeping the voltage drop low even at high voltages. This makes IGBTs far more efficient for high-voltage, high-current tasks.
The tradeoff is speed. MOSFETs can switch at 80 kHz and well beyond, making them ideal for compact power supplies, chargers, and smaller motor controllers. IGBTs typically operate below 80 kHz, with many high-power applications running at 20 kHz or less. At those frequencies, IGBTs handle far more power with lower losses than a MOSFET could manage at the same voltage.
In practice, the dividing line looks roughly like this:
- Below 20 kHz: IGBTs dominate. Trains, large EV motor controllers, grid-scale inverters, and large uninterruptible power supplies all sit here.
- 20 to 80 kHz: IGBTs are still common. Industrial robots, air conditioner inverters, and mid-size motor drives use them in this range.
- Above 80 kHz: MOSFETs take over. Laptop chargers, power tools, DC-DC converters, and small appliance motors are MOSFET territory.
Voltage and Current Ratings
Modern IGBTs span an enormous range of power levels. At the lower end, devices rated for 600 to 650 volts can handle currents up to 600 amps. Mid-range modules rated for 1,200 to 1,700 volts push that to 3,600 amps. For heavy industrial and grid applications, IGBTs rated at 3,300 volts handle 1,500 amps, 4,500-volt devices handle 1,200 amps, and 6,500-volt modules carry 750 amps. Devices rated above 10,000 volts are currently in testing.
To put those numbers in perspective, a typical household outlet delivers about 15 to 20 amps. A single high-end IGBT module can switch more than a hundred times that amount.
Where IGBTs Are Used
Electric vehicles are one of the biggest and fastest-growing markets for IGBTs. An EV’s battery stores energy as direct current (DC), but the electric motor runs on alternating current (AC). The inverter sitting between them uses IGBTs as its switching elements, rapidly toggling DC into a precisely shaped AC waveform that controls motor speed and torque. Renesas, one major semiconductor manufacturer, recently launched a new generation of IGBTs specifically targeting 400 to 800-volt EV inverters, reflecting how central these devices are to modern vehicle design.
Beyond EVs, IGBTs are workhorses across a long list of industries. Solar and wind power systems rely on IGBT-based inverters to convert generated DC power into grid-compatible AC. Industrial automation and robotics use them for precise motor control. Building automation systems, medical equipment, and even large home appliances like inverter-driven air conditioners depend on them. Trains have used IGBTs for decades to control traction motors, replacing older and less efficient thyristor-based systems.
The Three Terminals
If you’re looking at a circuit diagram, an IGBT symbol resembles a traditional transistor but with a distinctive insulated gate line. The three terminals are:
- Gate: The control input. A small voltage here turns the device on or off.
- Collector: Where the main current enters the device (in an N-channel IGBT, the most common type).
- Emitter: Where the main current exits.
The naming borrows “gate” from MOSFET terminology and “collector” and “emitter” from bipolar transistor terminology, reflecting the hybrid nature of the device. Most IGBTs you’ll encounter are N-channel types, though P-channel variants exist for specialized applications.
Thermal Management Matters
Because IGBTs handle such large amounts of power, heat is a constant engineering challenge. Every time the device switches on or off, and every moment it conducts current, some energy is lost as heat. At hundreds or thousands of amps, even a small voltage drop across the device translates into significant thermal output. That’s why IGBT modules in industrial and automotive settings are mounted on large heatsinks or liquid-cooling plates. The performance limits listed in datasheets assume adequate cooling. Without it, the device will overheat and fail.
This is also why switching frequency matters beyond just electrical performance. Higher switching frequencies mean more on/off transitions per second, and each transition generates heat. Designers choose the lowest switching frequency they can get away with for a given application, balancing smooth power delivery against thermal limits.