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This means that the I 2R drop across the bipolar output structure for a given switching current is much lower. But as the IGBT combines the low conduction loss of a BJT with the high switching speed of a power MOSFET an optimal solid state switch exists which is ideal for use in power electronics applications.Īlso, the IGBT has a much lower “on-state” resistance, R ON than an equivalent MOSFET.

The Insulated Gate Bipolar Transistor can be used in small signal amplifier circuits in much the same way as the BJT or MOSFET type transistors. Then we can treat the IGBT as a power BJT whose base current is provided by a MOSFET. Therefore, an FET’s gain is equal to the ratio of output current change to input voltage change, making it a transconductance device and this is also true of the IGBT. For a conventional bipolar junction transistor, (BJT) the amount of gain is approximately equal to the ratio of the output current to the input current, called Beta.įor a metal oxide semiconductor field effect transistor or MOSFET, there is no input current as the gate is isolated from the main current carrying channel.

The amount of amplification achieved by the insulated gate bipolar transistor is a ratio between its output signal and its input signal. Two of its terminals ( C-E) are associated with the conductance path which passes current, while its third terminal ( G) controls the device. We can see that the insulated gate bipolar transistor is a three terminal, transconductance device that combines an insulated gate N-channel MOSFET input with a PNP bipolar transistor output connected in a type of Darlington configuration.Īs a result the terminals are labelled as: Collector, Emitter and Gate. In effect it is an FET integrated with a bipolar transistor in a form of Darlington type configuration as shown. The advantage gained by the insulated gate bipolar transistor device over a BJT or MOSFET is that it offers greater power gain than the standard bipolar type transistor combined with the higher voltage operation and lower input losses of the MOSFET.

High-current and high-voltage bipolars are available, but their switching speeds are slow, while power MOSFETs may have higher switching speeds, but high-voltage and high-current devices are expensive and hard to achieve. IGBTs are mainly used in power electronics applications, such as inverters, converters and power supplies, were the demands of the solid state switching device are not fully met by power bipolars and power MOSFETs. The result of this hybrid combination is that the “IGBT Transistor” has the output switching and conduction characteristics of a bipolar transistor but is voltage-controlled like a MOSFET. The Insulated Gate Bipolar Transistor, (IGBT) combines the insulated gate (hence the first part of its name) technology of the MOSFET with the output performance characteristics of a conventional bipolar transistor, (hence the second part of its name).