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High-efficiency High-power-density 380V/12V DC/DC Converter with a Novel Matrix Transformer

Image of hardware prototype
Fig. 2. Hardware prototype.
Isolated high output current dc/dc converters are critical for future data center power architecture, however, the design is very challenging due to high conduction loss. Recently, the International Electronics Manufacturing Initiative (iNEMI), at the behest of IBM and other server manufacturers undertook a project to develop an industry standard for dc/dc converters. This converter is used to step down 380V directly to 12V with 800W output and is placed directly on the motherboard. The matrix transformers for the LLC converter in this application are investigated and a novel matrix transformer structure is proposed in this paper.

To improve the current design practice, a high-frequency transformer loss model is developed and a detailed design methodology is proposed. To overcome the challenge of multiple cores, a novel matrix transformer structure is proposed to integrate four elemental transformers into one magnetic core and utilize a simple four-layer PCB as the windings. The proposed design can utilize flux cancellation and reduce flux density in the magnetic plates to reduce core loss and to integrate SRs and output capacitors into the secondary winding, which minimizes leakage and termination loss. The core loss with the proposed matrix transformer is reduced by more than half when compared to the state-of-the-art matrix transformer technique. The proposed matrix transformer is superior to the state-of-the-art due to the much reduced core loss, simple four-layer PCB windings and integrated magnetic structure.

By pushing switching frequency up to MHz with GaN devices, the proposed matrix transformer can demonstrate the impact of a GaN in such important issues as efficiency, power density and manufacturability. With the academic contribution provided in this paper, we can design a converter with 10 or even 20 times the switching frequency, as compared to the current practice that uses silicon devices. Finally, a 1MHz 380V/12V 800W LLC converter with a GaN device using the proposed matrix transformer structure is demonstrated, as shown in Fig.1. The prototype fits in a quarter-brick footprint and achieves a peak efficiency of 97.6% and a power density of 900W/in3. With over 3 generations of LLC converter designs for this application, the efficiency has been improved continuously and our latest design can satisfy iNEMI's requirement with enough margin as shown in Fig. 2.

Image of efficiency improvement
Fig. 2. Efficiency improvement.
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