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Magnetic Integration of 3 kW LLC Converter for Front-end Power Supply in 48 V Power Architecture

Single-Phase LLC
Fig.1. Single-Phase LLC with matrix transformer for 3 kW 48 V power architecture
Power consumption at data centers is rapidly increasing in recent years. Lately, 48V power architecture is attracting more interest for data centers as it offers architecture that is both more efficient and contributes a telecom ecosystem. This paper focuses on the implementation of the dc/dc stage of a 3kW power supply unit. Single-phase LLC topology ( Fig. 1) is selected since it achieves soft switching; providing the opportunity to push the switching frequency and increase the power density. This paper focuses on the magnetic integration of the transformer and resonant inductor of the LLC converter. The paper discusses the design and magnetic integration of a matrix transformer. Three candidates of matrix transformers are discussed and evaluated, as shown in Fig. 2. A printed circuit board matrix transformer containing four elemental transformers is selected to efficiently handle the high power while maintaining high power density. The matrix transformer is integrated in one core along with a resonant inductor. The paper also addresses the matrix transformer winding layout to reduce leakage flux and current crowding in the windings. The secondary winding layout is modified to reduce current crowding in the matrix transformer. Careful layout of the primary side vias is also discussed and found to have good current shaing between the vias and reduce the current crowding around the vias. For the 48V power architcture, the dc/dc stage controls the output voltage within a range of 40 V to 60 V. A high resonant inductance value is introduced to gain voltage gain controllability. A resonant inductor is integrated with the transformer structure in one core to achieve a compact design. Optimization of the matrix transformer core loss and winding loss is also discussed and found to minimize total loss while achieving high power density. The proposed converter provides an estimated efficiency greater than 98 % with a power density greater than 400 W/in3.
Transformer Loss vs. Transformer footprint
Fig.2. Transformer Loss vs. Transformer footprint for three candidates of matrix transformer