Accurate Measurement of on-State Losses of Power Semiconductors

For safe design, the junction temperature should be kept within the specified range. Three methods are used most often for determining the power losses: 1. Calorimetric method; 2. Using calibrated heatsinks; 3. Electrical measurements of the device voltage and current, and finding the losses by integrating these variables. The paper concentrates on the third method with the emphasis given to the accurate measurement of the on-state voltage. The techniques of using non-linear dividers with deep voltage clamping are discussed. Novel circuits allowing faithful measurements of the on-state voltage along with good timing resolution of the switching transitions are proposed. Results of circuit simulations are borne out by extensive testing. Examples of measurement of the on-state voltage of large IGBT modules and free wheeling diodes (FWD) are presented. The obtained results are applicable for characterizing various power switches, e.g., gas discharge devices.