Transient overvoltage induced failure of MOS-controlled thyristor under ultra-high di/dt condition

Abstract

In this paper, the transient overvoltage induced failure during high di/dt discharge is studied based on a cathode-short MOS controlled thyristor (CS-MCT). The intrinsic reason of this failure is that the pulse current with high di/dt flowing though the inherent parasitic cathode inductance, produces a high transient overvoltage that makes breakage of the gate oxide. The mechanism of the transient overvoltage is theoretically detailed. A simple solution is proposed by adding a second emitter lead, which is called the Kelvin connection. The Kelvin emitter greatly clamps the overvoltage at high di/dt condition, preventing gate oxide from being broken down. The advantage of Kelvin connection against the normal connection was experimentally demonstrated and validated.