An Ultrafast Discrete Short-Circuit Protection Circuit for GaN HEMTs

Gallium Nitride enhancement-mode high electron mobility transistors (GaN E-HEMTs) are being designed into power electronic systems due to the fast switching capability. The GaN-based converters obtain higher efficiency, smaller size, and lower cost from the system point of view. On the other hand, the fast-switching characteristic of GaN also introduces the challenge of the short-circuit protection (SCP) and over-current protection (OCP). The traditional SCP/OCP methods are either too slow or not practical to the GaN device. Therefore, an alternative SCP/OCP solution which is fast and easy to implement is much desired for GaN HEMT. In this paper, an ultrafast discrete circuit of SCP for GaN HEMTs is proposed. The protection method includes two stages. The first-stage is soft turn-off, and the second-stage is hard turn-off. The soft turn-off can reduce the gate voltage gradually and thus limit the voltage spike on the DC-link. The method has been verified by both SPICE simulation and hardware implementation. The implementation results show that the propagation delay time for first-stage and second-stage are 85 ns and 125 ns, respectively. As a result, the proposed circuit is able to protect GaN HEMTs for short-circuit scenario under different DC-link voltages.