Time and Frequency Domain Characterization of Switching Losses in GaN FETs Power Converters

This work presents a methodology for the time-frequency characterization of the switching losses in Gallium Nitride Field Effect Transistors used in power electronics applications, particularly in DC-DC converters. Typically, switching losses are measured in the time-domain through the integration of the instantaneous power, that is, the product of the voltage multiplied by the current, during the turn-on and turn-off transients. Nonetheless, as novel power transistors allow for switching times in the nanosecond range, the accuracy of such measurements is compromised by the limitations of the probe-oscilloscope systems in terms of bandwidth and dynamic range. Here, we analyze the time-domain switching loss measurement method, and then, through a complementary setup it is demonstrated how to validate the results in the frequency domain. A DC-DC half-bridge buck converter circuit based in the EPC2001C was used as representative test sample. Less than 1% of difference in critical parameters such as rise-time, pulse width, state-levels and, switching frequency, is encountered between the time and frequency domain approaches. Moreover, the measurement uncertainty is analyzed and estimated to be between 1% and 8%. This work allows for highly confident switching loss measurements, a better understanding of the switching phenomena and of the measurement system performance.