Analysis of Output Capacitance Co-Energy and Discharge Losses in Hard-Switched FETs

The important distinction between stored energy and co-energy components of the output capacitance of field-effect transistors (FETs) is not explicitly discussed in the literature, and hence, less understood in relation to the switching losses in power electronic converters. An intuitive and detailed analysis of losses related to these energy components is presented in this work. It is shown that the co-energy component could cause a significant loss in a hard-switched device depending on the nature of circuit topology. A clear connection is established between the recently reported E
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loss mechanism in a hard-switched device and the co-energy. Furthermore, contrary to the conventional methods, a simple alternative method is proposed to calculate output-capacitance-related turn-on loss of a hard-switched device. The topology operates in no-load conditions, thus removing the effects of load current from the calculated losses. The method also has the added advantage of decoupling and separately calculating both stored and co-energy components, by a special selection of the complementary device in an inverter leg configuration. The concepts are validated with experimental results for a GaN-HEMT based inverter leg. They enable output-capacitance-related losses in hard-switching circuits to be treated in a more intuitive and straightforward manner.