A MOS-controlled high-voltage thyristor with low switching losses

A high-voltage phase-controlled symmetrical thyristor with MOS control was developed called the QCT. The QCT consists of two thyristor parts integrated on the same wafer; one MOS-controlled thyristor (MCT) with low conducting losses and a parallel conventional phase-controlled thyristor (PCT) with low switching losses. During the on-state both thyristor parts conduct the current. At commutation, the MCT-part is turned off, forcing the current over to the PCT. Thereby the QCT, even with high-voltage blocking capability, can have both low on-state losses and low switching losses, An experimental QCT for 5-10 kV has been designed and processed, having a diameter of 45 mm with a segmented MCT-part of 9-cm² area with high carrier lifetime to achieve low conduction losses and a 1.5-cm² PCT with low carrier lifetime to achieve low switching losses. The QCT has a conventional amplifying thyristor gate for turn-on and separate MOS-gates for turning off the MCT-part. The QCT was designed for a current handling capability of 400 A. It was shown that the reverse recovery charge could be reduced three to five times as compared to a device without this MOS-control