A Fast Short-Circuit Detection and Protection Method for Wide Band-gap Devices based on Current Derivative Sensing

Abstract

Over the years, robust Short-Circuit (SC) detection and protection methods have been developed for silicon (Si) devices, such as Si Insulated Gate Bipolar Transistors (IGBT) or Si Metal Oxide Field Effect Transistors (MOSFET). The emergence of Wide Band-Gap (WBG) devices as Silicon Carbide (SiC) MOSFETs and Gallium Nitride (GaN) High Electron Mobility Transistors (HEMT) brought the need of new protection methods. Indeed, the SC ruggedness of WBG devices is much lower than their Si counterparts. Moreover, the high switching speed of SiC and GaN devices requires special care regarding switching cell design. Indeed, reduction of parasitic inductance is a key parameter to fully take advantage of such components. However, low switching loop inductance can lead to very short transient before reaching the peak current during short-circuit (several hundred of Amps in few nano-seconds), making some usual SC detection methods inappropriate. On one hand, the most common method being the DeSat, may not be used as it stands for GaN. Indeed, the inherent delay time of these methods are inadequate. On the other hand, methods that are using direct current measurements, such as shunt, are also inappropriate due the degradation of the switching cell, being a key point with GaN devices. This paper proposes a fast analogue short-circuit detection and protection method for WBG devices, in particular GaN devices. The proposed circuit relies on current derivative sensing method. In fact, the current derivative pattern varies in case of short-circuit. The signal coming from the current derivative sensors is used to trigger the protection circuit placed as close as possible to the power device, shortening the protection delay time.