Instability analysis of enhancement-mode GaN based half-bridge circuits

This paper analyzes the problem of instability in enhancement-mode gallium nitride (GaN) transistors based half-bridge circuits. The instability may cause sustained oscillation, resulting in overvoltage, excessive EMI, and even device breakdown. This problem does not occur in silicon or silicon carbide transistors based circuit because of their different reverse conduction characteristics from GaN devices. GaN devices operate in the saturation region when they conduct reversely during the dead time. Under the influence of parasitic parameters, the GaN-based half-bridge circuit exhibits positive feedback under certain conditions, thus resulting in sustained oscillation. A small-signal model is proposed to study this positive feedback phenomenon. Based on the model, the influence of circuit parameters on instability are investigated and guidelines to suppress the oscillation are given. Finally, the analyses are verified by experiment.