Analysis of MOSFET Switching Losses in Resonant Converters Using Electrical and Thermal Measurements and Loss Trends with MOSFET Size Variation

Abstract:
The present work aims to implement a thermal method to measure the MOSFET power losses in an LLC resonant converter using silicon superjunction (SJ) MOSFETs with different die sizes. The difficulty in carrying out this type of thermal measurement lies in measuring a temperature as close as possible to the junction temperature. In this work, the junction temperature was measured through the temperature measured on an additional die that was copacked with the MOSFET for this purpose. On zero voltage switching (ZVS) converters, it is difficult to measure switching power losses only using oscilloscopes because there is no correlation between the value measured and the temperature. This quantity is measured by subtracting the known contributions from the total thermal losses. To better quantify the on-state losses, an on-state voltage measurement circuit (OVMC) is implemented to ensure that there are no significant errors that would otherwise be obtained from a high voltage probe. This circuit allows measurement of the conduction losses, the diode losses, and the R(DS(on)), which can be used also as temperature-sensitive electrical parameters (TSEP) to estimate the junction temperature from electrical measurement.