Online Junction Temperature Extraction for Cascode GaN Devices Based on Turn-On Delay

We introduce an innovative method for online junction temperature monitoring in cascode gallium nitride (GaN) devices, utilizing turn-on delay as the temperature sensitive electrical parameter for the first time on this device. The turn-on process is analyzed, and the expression of turn-on delay is derived, pointing out the factors affecting the turn-on delay. Following that, we provide a circuit implementation, along with an explanation of its operational principles. Thanks to the high resolution of the proposed method, a large auxiliary gate resistor used to improve the sensitivity is avoided. Furthermore, the avoidance of large gate resistors prevents triggering the self-sustained oscillations of cascode GaN devices. Finally, a comprehensive experimental verification is carried out. The results show that the proposed method has a short response time of 500 ns, a small static error of 2.3 °C and good dynamic performance. Besides, a dc power cycling was conducted to prove that the accuracy of the proposed method is not affected by device aging, proving its feasibility and applicability in practical applications.