IGBT

The newest member of the power semiconductor stable is the insulated gate bipolar transistor (IGBT). In power electronics there is a constant demand for compact, lightweight, and efficient power supplies, but these demands are not fully satisfied by power bipolars and power MOSFETs. High current and high voltage bipolars are available, but their switching speeds are poor. Power MOSFETs have high speed switching, but high voltage and high current modules arc hard to achieve.

The IGBT is a power semiconductor device introduced to overcome these limitations. It reduces the high on-state losses of the MOSFET while maintaining its simple gate drive requirements. It is controlled by the gate voltage as is the power MOSFET. But the output current characteristic is that of a bipolar transistor. These devices combine some desirable features of both the bipolar transistor and of the MOSFET.

In searching for the ideal power device, designers have considered many potential design concepts that combine the voltage control of the MOSFET gate with the superior conduction characteristics of the bipolar device. Of the many candidates there is only one that has become widely commercially available, the insulated gale bipolar transistor (IGBT). There is much research and development work in hand to implement improved versions of the IGBT, for example incorporating Trench Gates and making use of accumulation layer emitter effects, however this falls out­side the scope of this chapter where we will focus on the commercially available DMOS IGBT.

The IGBT employs injected-charge modulation in the base region and, due to the need for this charge to be extracted or extinguished at turn-off, has higher switching losses compared to the MOSFET. But as it can be realized at much higher power ratings it has become the power device of choice for a wide range of medium to high power electronic applica­tions. The main advantages of the IGBT arc the simplicity with which it can be driven (which is comparable to a power MOSFET), its lower on-state conduction losses and the capability of switching high voltages. These characteristics, together with the ability of IGBT to survive a wide reverse bias safe operating area (RBSOA) make it superior to the power MOSFET in high-voltage applications. Typically, IGBTs are used for switching circuits requiring high voltage (up to 3300 V) and high current (up to 3000 A), with a switching frequency of the order of 1-40 kHz.

Questionnaire:

• What is IGBT? Explain