What is an IGBT?

IGBT stands for insulated-gate bipolar transistor. Figure (a) shows the symbol of an IGBT. It is a power transistor that combines an input MOS and an output bipolar transistor. Figure (b) shows an example of the IGBT structure. A P region is formed on the drain side of the MOSFET. The resistivity of the high-resistance N^- drift region decreases when holes are injected from this P region at turn-on. This phenomenon is called conductivity modulation. Consequently, an IGBT is a switching transistor with low ON voltage even at high breakdown voltage.

Although its internal equivalent circuit is complicated, it can be simplified as consisting of an N-channel  MOSFET with variable on-resistance and a diode connected in series as shown in Figure (c).

The IGBT is a transistor ideal for high-voltage, high-current applications. Available with a voltage rating ranging from 400 V to 2000 V and a current rating ranging from 5 A to 1000 A^(*1), the IGBT is widely used for industrial applications such as inverter systems and uninterruptible power supplies (UPS), consumer applications such as air conditioners and induction cookers, and automotive applications such as electric vehicle (EV) motor controllers.

^(*1) IGBTs with up to 6 kV and up to 4500 A are also available for railway, high-voltage direct-current (HVDC) transmission, and other large applications.