NTE's series of Insulated Gate Bipolar Transistors (IGBTs) combine the high input impedance and high speed characteristics of MOSFETs and the high conduction (low saturation voltage) characteristics of bipolar transistors. Their structure looks very much like a MOSFET except that MOSFETs use an N+ - N- type substrate whereas IGBTs use a P+ - N- type substrate.
The thyristor fromed by PNP - NPN transistor coupling has its base and emitter shorted by aluminum patterning to disable it from operating and is therefore considered irrelevant to the basic operation of IGBTs. Consequently, the equivalent circuit and basic operating mechanism of IGBTs are the same as those of a MOS-input inverted Darlington transistor comprised of an N-channel enhancement MOSFET in its input stage and a PNP transistor on the output stage.
IGBTs are constructed in such a way that first, the gate voltage is applied to form a channel and then the base current of the PNP transistor is supplied, letting the circuit turn on eventually as an IGBT. Conversely, when turned off, the channel is eliminated to turn off the base current. Thus, IGBTs are driven in exactly the same way as MOSFETs, and IGBTs have high input impedance characteristics just like MOSFETs.