Influence of the selection of the approximating function of thermometric characteristics on the measurement results of thermal resistance of power mosfets

The paper describes the results of investigations illustrating the influence of the method of determining the excess of junction temperature and the selection of a function approximating the thermometric characteristic used in the procedure of measuring thermal resistance of a power MOS transistor on the measurement results. The investigations involved the measurements made using an indirect electrical method. Three methods of determining the excess of junction temperature of the transistor are presented, using a linear function and nonlinear function approximating thermometric characteristics. The thermal resistance measurement results obtained using each of the considered methods were compared. The measurement error caused by the selection of the considered methods was also analyzed.