Switching performance of GaN FETs in terms of turn-off resistance characteristics: an experimental study

Abstract

This study evaluated the AC parasitic capacitances and turn-off resistance of GaN FETs. Moreover, the study proposes an easily adjustable gate drive circuit appropriate for driving E-mode, cascode, and D-mode GaN FETs in the same driver topology. The proposed gate drive circuit involving only positive supply was established to provide not only a positive gate drive voltage to E-mode and cascode GaN FETs, but also a negative gate drive voltage to D-mode GaN FETs. This study also presents a simple circuit for shifting gate drive voltage levels to meet the driving voltage required for fully turning on or turning off GaN FETs. In cascode GaN FETs, the gate drive circuit incorporates additional resistor-capacitor-Zener diode (RCD) circuits applied to achieve a faster discharge rate, thereby increasing the switching speed by offering a negative turn-off voltage when the transistor is engaging in a turn-off process. In D-mode GaN FETs, the additional RCD circuits increase the drain current to enable the gate drive voltage to increase, resulting in the power transistor being turned on, thereby achieving a full conduction state to reduce on-state resistance. This paper presents comparisons of the switching performance of the different GaN FETs through the proposed gate drive circuit.