Detecting power-device State-Of-Health (SOH) during converter operation can enhance system reliability by predicting imminent failure scenarios. While various aging indicators for GaN devices have been demonstrated in the literature, few are practically measurable in an active converter. This paper demonstrates that the large-signal device output capacitance (Coss) is a reliable indicator of short-circuit (SC) aging, and proposes an in-situ measurement technique to capture its value by leveraging the operational waveforms in soft-switching converters. Experimental results show a 5% decrease in the large-signal Coss after 5000 SC cycles, proving the usefulness of this parameter as an SOH indicator. The in-situ measurement technique is demonstrated in a synchronous buck converter operating in discontinuous conduction mode, successfully capturing the SC-aging-induced change in Coss. The presented results and proposed measurement technique pave the way for system-level monitoring of power-device SOH and self-calibrating operation.
