A Simple De-saturation based Protection Circuit for GaN HEMT with Ultrafast Response

Similar to other power semiconductors, gallium nitride enhancement-mode high-electron-mobility transistors (GaN E-HEMTs) require short-circuit protection (SCP) or overcurrent protection (OCP) in practical applications. However, the fast-switching characteristic of GaN introduces the challenge to the protection. For SCP, the traditional methods are either too slow or not practical for GaN. Therefore, an alternative SCP solution, which is fast and easy to implement, is much desired. For high power density applications, it is also popular to integrate OCP into the gate driver. Therefore, a fast protection circuit that can be used for either SCP or OCP is desirable. In this article, an ultrafast discrete circuit-based protection circuit is proposed for GaN HEMTs. It includes a first soft turn- off stage and a second hard turn- off stage. The soft turn- off stage effectively limits the voltage spike over the device. Following the soft turn- off stage, the hard turn- off stage will cut off the pulsewidth modulation signal immediately completely. A dual-gate implementation approach is further proposed for devices with two gate pads. The method has been verified by both SPICE simulation and hardware implementations for both SCP and OCP. The experimental results show that the total propagation delay time for SCP is only 125 ns while the normal switching performance is not affected.