IGBT – a Darlington configuration consisting of an FET and bipolar transistor

When voltages and currents were connected with bipolar transistors in the past, there were two options: you could connect low currents with low control currents or large currents with large control currents. If you needed to switch large currents using small control currents, the solution would be a transistor cascade, also known as a Darlington configuration. Here, the first transistor acts as an amplifier for the control signal, thus activating the switching of large currents using small control currents.

Developed at a later point in time, field effect transistors no longer need any currents to control – they are opened by connecting a voltage and by the electric field generated as a result. 

Combining a FET and a bipolar transistor united the advantages of both worlds, giving rise to the IGBT.