Vias Placement Strategy for High Power Transformers with Vertically Stacked PCBs

Isolated DC-DC converters in data centers have a high step-down ratio. This causes large high-frequency currents on the secondary side. But strong proximity effect occurs in the wires between the transformer and the rectifier. These effects cause large losses. To address this issue, an approach has been proposed to suppress proximity effect by designing the transformer windings on a PCB and directly attaching the rectifier elements to the windings. In this approach, it was assumed that PCBs would be connected in parallel in the vertical direction to compensate for the small cross-sectional area of the PCB windings. However, when connecting PCBs using vias, there is a concern that unexpected losses may occur due to proximity effects near the vias, magnetic coupling between PCBs, or other proximity effects. In this paper, after measuring the AC resistance of prototype devices with different via placements and PCB spacings, we analyze the mechanisms of loss increase using electromagnetic field analysis and provide multiple strategies for designing PCB layering.