6.1 Introduction
The Insulated Gate Bipolar Transistor, or IGBT, is a power semiconductor that first became available to the commercial market during the 1980s. Initial devices had certain performance issues but these problems largely have been taken care of with subsequent generations. Today, the IGBT is in wide use, competing with power BJTs and power E-MOSFETs across a range of applications. The IGBT is designed to be used as a high voltage/high current switch and typically is not used for linear applications such as an audio class B power amplifier. The IGBT has also overtaken the older thyristor devices (e.g., SCR) in many areas due to its speed and the relative simplicity of the driving circuits used to control it.
The IGBT offers a mix of performance characteristics of both the power BJT and the power E-MOSFET. Like the BJT, the IGBT offers low on-state power loss and the ability to handle large currents and voltages. Like the power E-MOSFET, it is relatively easy to drive, being a voltage-controlled device rather than a current-controlled device. On the down-side, it is not as fast as the current generation of power E-MOSFETs and tends to be more costly than both the power BJT and power E-MOSFET. Consequently, the choice of which of these three devices should be used for a given power switching application will depend on the specifics of the design. For example, a medium to high power design that focuses on lowest cost may favor the BJT, a low to medium power application that requires very high switching speeds may be best solved with a power E-MOSFET, while an IGBT might be ideal for a very high power application utilizing low to medium speed clocking. This chapter will examine a number of power switching applications, and while they will all revolve around using the IGBT, please bear in mind that, depending on the specifics, power BJTs and E-MOSFETs might also be used.
The IGBT is available in two variants: the punch through, or PT; and the non-punch through, or NPT, versions. We shall look at both.
