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Active-Device Losses in Resonant Power Converters: A Case Study with Class-E Inverters

Recent research has reported an undesirable OFF-state loss in high-frequency soft-switching power converters, such as resonant converters. This loss is attributed to a hysteresis loss related to the charging-discharging process of the output capacitance of the power transistor. However, precise estimation of transistor power loss and its breakdown into ON-state and OFF-state losses is challenging in the MHz-range operation due to the small circuit size, parasitic effects, and limited accuracy in existing methods to measure low-loss systems. We present a measurement concept to perform a complete loss breakdown of MHz-range resonant converters, as well, directly determine the OFF-state losses in transistors, which is demonstrated for a GaN-based class-E inverter operating at 10 MHz. A novel and compact calorimeter was designed to measure the converter active-device losses down to 20 mW within a 5% error. This measured loss is then separated into four components using a combination of average and instantaneous electrical measurements: transistor ON-state loss, transistor OFF-state loss, gate-driver internal loss and gate loss. A simple no-load technique was devised to evaluate the gate-driver internal loss. The proposed approach directly determines output-capacitance hysteresis losses during the actual converter operation, which is not possible with existing measurement methods. The presented knowledge of individual loss components permits better optimization of MHz-range power converters.