對於高降壓比LLC串聯諧振轉換器的整體損耗來說，磁性元件為主要來源之一。因此為了追求高效率及高功率密度，改善磁性元件為重要的課題。鐵氧磁體鐵心具有高導磁係數及低鐵損等優點，因此廣泛的應用在高頻切換式電源上。高頻鐵氧磁體鐵心主要損耗為磁滯損與渦流損，本文透過軟體Maxwell利用有限元素法來分析和優化鐵心結構，改變磁通密度的分佈降低鐵心損耗，在增加鐵心體積和降低鐵心損耗之間取得平衡點，使變壓器能夠達到最佳化設計，優化電路效率的目標。最後將不同架構鐵心實作在一台切換頻率500 kHz，380 V輸入轉12 V輸出功率750 W ，LLC串聯諧振轉換器，以驗證模擬與實測結果是否一致。

Magnetic components are the main source of power losses in high step-down LLC resonant converters. Therefore, to achieve high efficiency and high power density, improving the magnetic element is an important issue. Ferrite cores with high permeability and low core loss are widely used in high-frequency switching power supplies. The core loss mainly results from hysteresis loss and eddy current loss. Therefore, this thesis aims to analyze and optimize the structure of ferrite cores using Maxwell software to implement the Finite Element Method (FEM). Changing the distribution of magnetic flux density to reduce core loss results in a tradeoff design between the volume and loss of magnetic core. Then, the transformer can be optimized to achieve high circuit efficiency. Finally, a 750-W LLC resonant converter prototype with specifications of 380-V input voltage, 12-V output voltage, and 500-kHz switching frequency is implemented and tested to verify the feasibility of different architectures on transformer cores.

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