Electrothermal Characterisation and Analysis of a Power Transistor for Thermal Runaway Prediction

Transistors represent some of the most common and vital components in power electronics, playing a crucial role in the design of power converters. This thesis provides a comprehensive and in-depth study of these devices, specifically focusing on the self-heating phenomena that characterise their operation. When active, transistors undergo significant temperature increases following a progression that is not always linear with respect to current. Such overheating can reach a state of instability, culminating in thermal runaway and the subsequent catastrophic failure of the component. The core of this research involves investigating this phenomenon within a 22 mΩ TO-247 MOSFET to develop a MATLAB predictive model for thermal runaway. This tool aims to significantly reduce the time required to identify operational boundaries while preventing the destruction of multiple components during experimental bench testing. Concurrently, an analysis of the contribution of parasitic electrical resistances was conducted to enhance the accuracy of the results. This further serves to demonstrate the measurement discrepancies observed at the test bench when utilising the Kelvin pin versus the Power source pin of the aforementioned transistor.