A Novel Cascode-Diode-Based Functional Multiplexing Circuit for Both Efficient Freewheeling and Accurate on-State Voltage Extraction for IGBTs

Insulated-gate bipolar transistors require antiparallel diodes for freewheeling and on-state voltage measuring circuits (OVMCs) for condition monitoring. This letter presents an innovative cascode-diode-based functional multiplexing circuit that concurrently serves as both a freewheeling diode (FWD) and an OVMC. It reduces the number of high-voltage components by over 50% and lowers overall cost compared to conventional schemes with separate FWDs and OVMCs. When functioning as an FWD, the proposed circuit performs comparably to SiC Schottky barrier diodes. As an OVMC, it has high accuracy (relative errors ≤0.2‰) and a fast dynamic response time (≤ 128 ns). Operation principles and design guidelines are discussed in detail. Experiments with a 1200 V/30 A prototype confirm its feasibility and advantages.