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Active dv/dt Control of 600 V GaN Transistors

Schematic of control circuitry for dv/dt
Fig. 1. Proposed turn-off (left) and turn-on (right) dv/dt control circuit.
The application of fast-switching devices like the GaN HEMT in power converters allows converters to achieve a higher switching frequency, a higher efficiency and a higher power density. As a result of the fast switching edge and high commutation speed, issues like electromagnetic interference (EMI), overvoltage, and gate protection become daunting tasks. The active gate control technique on the Si device has been verified 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 a 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. The proposed circuits are shown in Fig. 1. Simulations are first performed to verify the circuit function while considering all the possible parasitics distributed on the experimental setup, and a detailed circuit design follows. The hardware is illustrated in Fig. 2. Experimental results, shown in Fig. 2, obtained on the 300 V 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, a comparison with different gate resistors is provided, showing the proposed method has a smaller switching loss under the same dv/dt condition rather than using a large gate resistor.

Two images showing a designed PCB of a double pulse tester, and a second waveform of the waveforms from the test circuit
Fig. 2. Left: hardware for Double pulse test with active dv/dt control circuit; Right: DPT turn-off Vds wave-forms at 300 V dc 15 A load current with active gate driver.
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