Advanced Overcurrent Detection with Digital Controllable Blanking Time for Fast SiC-Switch Protection

Abstract:
Power semiconductors devices are sensitive to short circuit occurrences even in normal operation conditions. Si IGBTs have been designed to withstand short circuit at least 10 mus, which was detected by simply desaturation circuit. The desaturation circuit basically consist of high voltage diode, voltage comparator and RC filter for blanking time adjustment and noise suppression. Such a detection circuit doesn’t allow precise detection of overcurrent or short circuit event. The SiC MOSFETs generally can’t withstand short circuit longer than 1mus…3mus. However, it is possible to reduce detection time and to increase accuracy of desaturation detector. This paper presents fast overcurrent protection circuit based on SiC-MOSFET Miller-Plateau monitoring during turn-on period. Gate sense circuit monitors gate voltage and detects transition above adjustable voltage threshold, before triggering digitally programmable blanking time. Selected voltage threshold is set slightly above Miller Plateau voltage, signalizing the end of turn-on transition. Digitally programmable blanking time is selectable between 0ns and 700ns with 100ns steps. Both, gate sense monitoring and digital blanking time adjustment allow fast and precise overcurrent protection.