Before the development of Insulated Gate Bipolar Transistors power electronics engineers relied mainly on two types of devices for fast and high frequency switching namely the Bipolar Junction Transistor and the Metal Oxide Semiconductor Field Effect Transistor. Both BJTs and MOSFETs were capable of switching at higher frequencies compared to thyristors or SCRs. However each technology had its own limitations.
MOSFETs offered very high switching speeds which made them suitable for high frequency operation. However designs intended for high voltage and high current applications were relatively costly and less efficient. BJTs on the other hand were available in high voltage and high current configurations but generally suffered from lower switching speeds compared to MOSFETs.
Insulated Gate Bipolar Transistors or IGBTs were developed to combine the strengths of both technologies. An IGBT can be considered as an insulated gate N channel MOSFET coupled with a PNP Bipolar Junction Transistor. This structure allows the IGBT to deliver high voltage and high current capability similar to a BJT while retaining the voltage controlled gate characteristics of a MOSFET. This combination enables efficient operation at higher switching frequencies.
An IGBT is a three terminal switching device consisting of the Emitter the Gate and the Collector. Current conduction occurs between the Collector and the Emitter. Similar to a thyristor the IGBT allows controlled current flow when a signal is applied to the Gate. However unlike a thyristor which is current controlled and latches on once triggered the IGBT is voltage controlled. It conducts when a positive voltage is applied to the Gate and switches off only when the Gate voltage is reduced to zero or driven negative.
The output current and voltage characteristics of an IGBT are similar to those of a BJT. However the voltage controlled gate inherited from the MOSFET simplifies the drive circuitry and improves switching performance. One major advantage of the IGBT over a conventional MOSFET is its lower on state voltage. The conduction channel resistance in an IGBT is significantly lower which allows much higher current ratings compared to a similarly rated power MOSFET.
IGBTs are therefore an excellent choice for switching high currents and high voltages in power electronics systems. They are typically used in power applications above 1kW where standard MOSFETs and BJTs begin to reach their practical limits. IGBTs commonly operate at switching frequencies ranging from 1kHz to 20kHz.
Low voltage applications below 600V are usually high volume and consumer oriented. Examples include motor drive control in household appliances such as washing machines. Higher voltage applications are more common in industrial and transportation sectors. Typical operating voltages include 1200V and 1700V which are standard ratings for many industrial IGBT devices.
Key application areas for IGBTs include electric vehicles rail traction systems industrial motor drives renewable energy systems and power conversion equipment. In many of these applications IGBTs are not used as single discrete devices. Instead they are assembled into IGBT modules which integrate multiple devices to form complete power control circuits. This modular approach improves power density simplifies system design and enhances overall reliability.
