Impact of Gate Turn-Off Voltage on Body Diode Loss of SiC MOSFET and a Scheme to Improve Light Load Efficiency of SiC Converters

SiC MOSFET’s body diode drop is typically 2-3 times more than Si-based PiN diode of similar rating. This leads to higher losses in the body diode of SiC MOSFET which reduces the converter’s efficiency. The reduction in efficiency becomes significant when the converter operates in discontinuous conduction mode (DCM) during the light load operation. Further, the body diode drop in SiC MOSFET is dependent on the gate turn-off voltage ($V_{EE}$) and it increases as $|V_{EE}|$ increases. Conventionally gate drivers for SiC MOSFET use a high value of $|V_{EE}|$ to prevent Miller turn-on. However, a high value of $|V_{EE}|$ increases the diode losses, which further reduces the efficiency. This manuscript investigates the impact of $V_{EE}$ on the body diode loss in a SiC MOSFET. Furthermore, it proposes a scheme to select an optimum $V_{EE}$ to reduce body diode loss while mitigating the possibility of Miller turn-on. To facilitate the development of the proposed scheme, this manuscript- (i) investigates the dependence of the body diode drop on $V_{EE}$ for SiC MOSFET using device physics-based analysis. Further, it validates the same using static characterisation of commercial SiC MOSFET. (ii) it presents a detailed mathematical analysis to estimate the overshoot in gate-source voltage due to the Miller effect. The proposed scheme is experimentally validated on a buck converter operating in DCM (10% of rated power). Operation with the optimal $V_{EE}$ obtained using the proposed scheme shows a 2.32% improvement in efficiency over conventional designs.