Driving of a GaN enhancement mode HEMT transistor with zener diode protection for high efficiency and low EMI

The ultra-low gate charge characteristics and low gate voltage limitation of a GaN enhancement mode HEMT in combination with stray circuit elements poses many challenges of driving them in power electronic applications. This paper investigates the effect of changing gate resistances and including a Zener diode for overvoltage protection in the gate circuit. The goal is to achieve low switching losses and low EMC signature. Due to the very low gate capacitance of the GaN HEMT compared to the junction capacitance of the Zener diode, the addition of the Zener diode has an effect on the switching waveforms. The effects were investigated through simulation and measurements on a 1 kW PFC boost converter. The Zener diode was shown to increase time delay between the PWM signal and the switching of the GaN device. Furthermore, both fall and rise times of the drain-source voltage were influenced. Efficiency and EMC measurements highlight that the choice of gate resistor is an optimization problem, as faster switching increases efficiency but increase the EMC signature of the converter.