A Novel Isolated Resonant Gate Driver With Adjustable Duty Ratio for SiC MOSFET

Resonant gate driver is a promising technique to save gate driver loss at high switching frequencies to further promote the integration level of gate driver with power modules. State-of-the-art isolated resonant gate drivers (RGDs) have to keep duty ratio fixed at 0.5 to avoid transformer saturation, which significantly limits the practical applications. A new isolated RGD (IRGD) with adjustable duty ratio to drive silicon carbide (SiC) MOSFET is proposed in this article by employing switching period expansion technique with a dual-secondary transformer. Transformer secondary windings are involved in the turn-on and turn-off processes alternatively and are switched at the falling edge of each input driving cycle. The effective switching frequency at gate driver transformer is reduced to 1/2 to further save power losses at high switching frequencies. This article further discusses the optimal damping approach to suppress $v_{\mathrm {gs}}$ overshoot and oscillation due to an adjacent second driving stage brought by parasitic gate resistor for IRGDs. The proposed IRGD is built with printed circuit board (PCB) integrated planar transformers, designed at leakage inductance of 303 nH with primary-side silicon (Si) devices and secondary bidirectional gallium nitride (GaN) devices. The duty ratio is proven to be adjusted from 0.15 to 0.9. The power consumption of the prototype is 0.883 W at 500 kHz and 1.473 W at 1 MHz driving a 900-V SiC device with 87-nC gate charge, which is $6\times $ less power consumed than a conventional gate driver (CGD). The adopted SiC power device achieves dv/dt on of 18 V/ns and dv/dt off of 35 V/ns with the proposed IRGD.