Active dv/dt control of 600V GaN transistors

With the fast-switching devices like GaN HEMT applying in power converters, the converters achieve higher switching frequency, higher efficiency and higher power density. As a result of the fast switching edge and high commutation speed, the issues like electromagnetic interference (EMI), overvoltage, gate protection become daunting tasks. The active gate control technique has been verified on the Si device to be an effective tool to relieve the challenges above, especially to reduce EMI noise by slowing down dv/dt with less penalty of switching loss. The paper proposes a new active dv/dt control circuit with fast response to change the 600 V GaN HEMT turn-off and turn-on dv/dt slew rate freely and independently, while the converter is running. To achieve this, simulations are first performed to verify the circuit function, considering all the possible parasitics distributed on the experimental setup, and a detailed circuit design is followed. Experimental results obtained on the 300V dc 15 A load current double pulse tester, composed by a GaN HEMT phase leg, validates the proposed method by varying turn-on dv/dt slew rate from 27.1 V/ns to 8.8 V/ns, turn-off dv/dt from 34.6 V/ns to 7.6 V/ns. Finally comparison with different gate resistors is provided, showing the proposed method has a smaller switching loss under the same dv/dt condition than using a large gate resistor.