A T-Shaped High Isolation Gate Driver Power Supply for Medium-Voltage SiC Half-Bridges

For medium-voltage wide bandgap devices, the interdependence between isolation capability and coupling capacitance is the major barrier to compact and insulation-reliable gate driver power supplies (GDPS). This article proposes a loosely coupled transformer with a customized T-shaped core and printed circuit board (PCB) coils, achieving high isolation and low capacitance within a limited footprint. Dual-output PCBs are oriented to reinforce the isolation between multiple coils, while orthogonal placement minimizes parasitic coupling. Bulk field grading is applied with an internal layer to reduce the electric field (E-field) stress, as well as alleviate the triple point. Finally, circuit decoupling is used to address the cross-coupling between multiple outputs, so that a quasi-constant voltage is available in each output channel against varying load while unregulated. The solution is tailored for a typical SiC half-bridge, which achieves a partial discharge inception voltage of 30 kV RMS with a minimal primary-to-secondary distance of 9.5 mm, a coupling capacitance of 2.65 pF, and an output power of 20 W per channel. The GDPS also supports self-regulated power delivery under slew rates of up to 180 kV/μs, indicating its high common-mode transient immunity level.