An analysis of paralleled SiC bipolar devices

SiC semiconductor devices are becoming more common in high power applications. This is largely due to higher blocking voltages and faster switching speeds. The development of SiC devices, specifically thyristors and GTOs, is still an evolving process [1]. There is not yet a single device capable of handling the magnitude of current typically seen in transmission and distribution systems and as a result these devices must be paralleled into a single switching position. SiC thyristors were used to carry out a study on paralleled SiC bipolar devices. Si bipolar devices are much better matched than SiC devices, but they exhibit much slower turn-on times [2]. Thus, the most suitable method of inducing current sharing in these devices is through gate control. However, SiC devices exhibit fast turn-on times while being poorly matched. Using various methods of gate control for SiC bipolar devices in parallel does not significantly affect the current sharing. The best way to improve current sharing is obtained using series resistors. These resistors should be chosen so that the voltage drop and power losses are minimized. The effects of thermal runaway are observed as well. As a device rises in temperature relative to the other devices, it conducts more current due to its negative temperature coefficient of on-state resistance. In order to maintain proper heat sharing, a design for a package is presented that includes three thyristors in parallel on a common substrate.