Turn-on Delay Based Real-Time Junction Temperature Measurement for SiC MOSFETs With Aging Compensation

摘要

Online junction temperature (T-j) measurement enables robust power converter operations by providing overtemperature protection and condition monitoring of the power devices. For SiC MOSFETs, the real-time T-j information is especially critical as limited field data are available regarding the reliability. In this article, utilizing the turn-ON delay time as temperature sensitive electrical parameter, an online T-j measurement is realized through an intelligent gate drive. Specifically, the turn-ON delay time is translated into the pulsewidth of a digital signal through the conditioning/logic circuits. During Tj measurements, the adjustable gate resistance circuit is activated to improve the measurement sensitivity beyond 600 ps/degrees C. Using the high-resolution capture module (300-ps resolution) in the system microcontroller, this pulsewidth is measured and then converted to junction temperature with a resolution of <0.5 degrees C. A prototype is built to validate the online T-j measurement method. The switching test results show that the circuit is able to precisely measure T-d,T-on and offers a good linearity/sensitivity for T-j estimation. In the continuous operation, the junction temperature of a decapsulated device using an infrared camera and T-j obtained from the circuit match well with <1 degrees C difference under various operating conditions. In addition, the gate-oxide degradation's impact on T-d,T-on is considered for SiC MOSFETs, and an aging compensation scheme is discussed to maintain the measurement accuracy throughout the device's lifetime. It is shown that the proposed circuit provides an accurate real-time Tj measurement for SiC MOSFETs, which can be deployed to improve the power converters' reliability.