Thermal Resistance Meter for Power Transistors With Heating Power Modulation

This article describes a meter for measuring thermal resistance of power transistors. It was developed to research the thermoelectric properties of power MOSFETs. The research was performed with the use of standard thermal resistance measurement methods and with the novel modulation method, which heats the device under test (DUT) with harmonically pulsewidth modulated current pulses. The temperature-sensitive parameter (TSP) was measured in the pauses between pulses. Voltage USD on the closed transistor’s channel was used as TSP for power MOSFETs. To eliminate the influence of the delay time on the results of thermal resistance measurements, the TSP values were extrapolated to the end of each heating pulse. For extrapolation, it is proposed to use the root and logarithmic laws of the TSP changing in the process of transistor die cooling after heat impulse. The results of the thermal resistance components measurements obtained by various methods are in good agreement (about 2%) with each other.