In a capacitor-assisted soft-switching converter, the zero-voltage turn-on (lossless) of the complementary MOSFET is lost at low values of load current, and it incurs a significant amount of turn-on loss. This phenomenon is termed as the partial hard turn-on, and it is a special case of soft-switching dynamics. Estimation of partial hard turn-on loss is essential for predicting light load efficiency of any soft-switched converter. However, direct experimental measurement is not accurate due to the presence of circuit parasitics. Also, it is difficult to measure waveforms of high-side devices due to high-frequency common-mode voltage. In this paper, an alternate energy-based method is proposed to estimate the partial hard turn-on loss of the complementary MOSFET using experimental data. This method is derived from the behavioral model through approximations. Although indirect, this method results in a simple and accurate estimation of partial hard turn-on loss from measured waveforms. The proposed energy-based technique is verified through behavioral simulation and experiment for a 39A, 1200V SiC MOSFET for a wide range of operating conditions.
