Evaluating On-State Voltage and Junction Temperature Monitoring Concepts for Wide-Bandgap Semiconductor Devices

Monitoring or estimating the junction temperature of power semiconductor devices is a requirement for degradation monitoring and predictive maintenance of power-electronic converters and usually achieved by online measurement of a temperature-sensitive electrical parameter (TSEP). Many TSEPs rely on switching transients and, thus, depend on the design of a switching cell, driving significant calibration efforts. Instead, utilizing the on-state voltage of a power semiconductor device as TSEP is attractive, as it only depends on the load current and the output characteristic of the device. This independence of the switching cell design enables on-state voltage monitoring circuits to be seamlessly integrated into products that are already mass produced. However, an effective on-state voltage monitoring circuit has to measure small on-state voltages accurately and fast while withstanding high off-state voltages. This article experimentally evaluates three candidate circuits that take on this challenge: a circuit derived from a Wheatstone bridge, a dynamically compensated voltage divider, and a circuit using an auxiliary MOSFET. PCBs are designed, featuring all three circuit concepts, and experiments are carried out to compare the candidate circuits in terms of dynamic performance and resolution. Finally, the potential for integration into commercial products is outlined, illustrated, and discussed.