What is an IGBT?

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Editorial Team - everything PE

Sep 12, 2021

IGBT or Insulated Gate Bipolar Transistor is a voltage-controlled semiconductor device that is designed for fast switching applications. It consists of three terminals – gate, collector, and emitter. An IGBT is a hybrid of BJT and MOSFET as its input side represents a MOSFET with a gate terminal and the output side represents a BJT with collector and emitter terminals. 

IGBTs are ideal for low to medium power applications such as traction inverters for HEV/EV, auxiliary DC/AC converters, switched-mode power supplies, refrigerators, industrial motors, automotive main motor controllers to improve their efficiency traction motor control, induction heating, and power train systems requiring fast switching.

Key features of IGBT:

  • Low on-state voltage as compared to the BJT (bipolar junction transistor).
  • Lower switching losses.
  • Lower conduction losses.
  • Ease of gate drive.
  • Peak current capability.
  • Ruggedness.
  • Faster switching than BJT.

IGBTs can be classified into the following:

PT (Punch Through) – Punch-through IGBTs are those that have an n+ buffer layer. These IGBTs are used in inverter and chopper circuits and have symmetrical voltage blocking capabilities.

NPT (Non-Punch Through) – Non-punch through IGBTs are those that don’t have an n+ buffer layer. They are used in rectifier applications and have symmetric voltage blocking capabilities.

Symmetrical IGBTs - These IGBTs have equal forward and reverse breakdown voltage and are mostly used in AC circuits.

Asymmetrical IGBTs – These IGBTs have a reverse breakdown voltage less than the forward breakdown voltage. They are commonly used in DC circuits.

Key Specifications of IGBT:

Collector-Emitter Voltage: It represents the voltage drop that occurs between the collector and the emitter terminals and is expressed in volts (V).

Saturated Collector-Emitter Voltage: It represents the maximum voltage drop that occurs between the collector and emitter terminals and is expressed in volts (V).

Gate Emitter Voltage: It represents the voltage drop that occurs between the gate and emitter terminals and is expressed in volts (V).

DC collector Current: It represents the amplified output current that flows through the collector terminal of an IGBT and is expressed in Ampere (A).

Peak Collector Current: It represents the maximum collector current that can be handled by the IGBT and is expressed in Ampere (A).

DC Forward Current: It represents the current that the diode part inside an IGBT requires to conduct at room temperature conditions. It is expressed in Ampere (A).

Peak Forward Current: It represents the maximum peak current that the diode inside an IGBT requires to conduct. It is expressed in Ampere (A).

Gate Emitter Leakage Current: It refers to the leakage current that occurs due to the voltage drop between the gate and emitter terminals.

Power dissipation (W): It represents power dissipated by the IGBT. It is equivalent to the product of collector current and collector-emitter voltage and is measured in Watts (W).