Unclamped-inductive-switching Based Output Capacitance Loss Characterization with Extended Test Capability

Abstract

Output capacitance (COSS) loss (EDISS) is a power loss recently revealed in a power semiconductor device when its COSS is charged and discharged, which ideally should be a lossless process. Considerable EDISS has been reported in various power devices for high-frequency soft-switching operations. Up to now, a few methods have been proposed for EDISS measurements under distinct device operations; however, the relation of the test results from these methods remains unclear. In some methods, the device remains OFF, and its EDISS is measured similarly to that of a passive capacitor. In some other methods such as the unclamped inductive switching (UIS), the device switches ON and OFF in the steady state during the EDISS measurement. This work proposes a novel test scheme based on the UIS method to characterize the active power devices in both the always-OFF and active-switching conditions. Three devices, i.e., a Si superjunction FET, a SiC MOSFET, and a GaN HEMT, are tested. A nearly identical EDISS is found under the two conditions with the same switching current for all these devices. This suggests that EDISS is mainly determined by the OFF-state capacitive current instead of the ON-state conduction current. In addition, while the UIS method was only applied to transistors previously, this work demonstrates a new test scheme to characterize the EDISS of a power diode using the UIS method. These results showcase the wide capability and simple implementation of the UIS-based EDISS measurement, as well as provide new physical insights into the EDISS origins.