Highly Efficient 800-to-48-V LLC-DCX With Matrix Transformer Using Side Leg Windings

Adding side legs to matrix transformer to achieve magnetic flux diversion and improve core utilization can effectively reduce core losses. The current approach of optimizing air gap is challenging in manufacturing and adjusting parameters. This paper proposes a side leg windings solution to naturally divert flux and achieve flux averaging among all legs, where off-the-shelf core can be applied to facilitate fabrication. Additionally, the side leg windings are connected in series to enable adoption of low voltage devices with better NFoM. It helps improve efficiency in a high voltage application. Finally, the proposed structure is verified on an 800 V to 48 V, 3 kW LLC-DCX prototype, achieving a peak efficiency of 98.5% and a power density of 650 W/in3.