Dynamic Optical Turn-Off Control of a High-Voltage SiC MOSFET

This paper presents a novel self-contained optical turn-off control method for high-voltage SiC MOSFETs, used in the next generation high-power and high-frequency power-electronics applications. Turn-off control decreases the turn-off voltage overshoot and ringing caused by adverse current slope and controls turn-off dv/dt to reach the optimal or desired point in terms of electro-magnetic interference (EMI), switching losses, and device stress. In contrast to other works, the proposed control method dynamically and independently controls the turn-off dv/dt as well as turn-off voltage overshoot and ringing in different operating conditions using a single circuit. The moment of transition between dv/dt and voltage overshoot control is accurately initiated by a delay compensation circuit based on turn-off dv/dt. Another feature of the presented work is using a high-frequency laser driver, laser and optical link to send the control signal to a hybrid package consisting of a SiC MOSFET being triggered using two optically-trigged power transistors (OTPTs). The direct optical link precludes the possibility of signal corruption by external EMI. Further, optical (intensity) modulation of the OTPTs, which charge and discharge the SiC MOSFET's gate, enable variable charging and discharging response times for the SiC MOSFET. The proposed control circuit operation and advantages are presented and verified by experimental and numerical results.