Rugged and fast short circuit detection method for GaN HEMT based on saturation detection

Abstract:
In this paper a rugged and fast short circuit detection method for Gallium Nitride High Electron Mobility Transistor (GaN HEMT) based on a saturation detection with gate- and drain-source voltage monitoring is presented. GaN HEMTs fail under short circuit condition at high dc-link voltages in several hundred nanoseconds. A first adoption of a state of the art desaturation detection circuit with high voltage (HV) desat-diode and reference voltages up to 31V has shown false triggering due to low EMI immunity and slow decreasing drain-source voltage at high currents and case temperatures. Hence, a new, more rugged circuit using an RC voltage divider for drain-source voltage monitoring enables high bandwidth measurement and high EMI immunity. The new rugged and fast short circuit detection method uses a high saturation reference voltage of about 180V considering high transient drain-source on-state voltages of the used GS66516T GaN enhancement mode HEMT (eHEMT) especially at excess currents and high case temperatures. Further, the EMI robustness has been improved by eliminating the HV desat-diode.