Electronic Circuits for Switching-time Reduction of Bipolar Semiconductor Devices

Bipolar semiconductor devices are often used as switches in very high power electronic circuits and systems. They have replaced the old conventional gas filled tubes and vacuum devices in many applications. This is mainly due to the fact that solid-state devices are more efficient, smaller in size, cheaper and more reliable. In addition, solid-state devices are considered environmental friendly, since they do not contain nasty gases and toxic materials used in old devices.

The power level requirements and switching frequency are continually increasing in the power electronic industry, and this demands larger and faster switching devices. As a result, both bipolar and unipolar semiconductor devices have undergone continued improvement in current and voltage ratings, and switching speed. The main advantage of bipolar devices is their low conduction losses due to conductivity modulation, but their main disadvantage is the high switching losses which is due to minority carrier injection.

The Insulated Gate Bipolar Transistor (IGBT) combines the advantages of both unipolar and bipolar devices. It has a simple gate drive circuit like that of the MOSFET, with high current and low saturation voltage capability of bipolar transistor. The main problem remains with the relatively long tail turn-off current. To reduce the turn-off time of the IGBT and other bipolar devices, different lifetime control techniques and structural changes have been developed and used. Details of these and new techniques developed by using auxiliary electronic circuits for reducing the turn-off time and increasing the switching speed of bipolar semiconductor devices are presented in this paper.