對於高降壓比、高輸出功率的LLC電路來說，主要的功率損失來自於二次側的繞組線損以及鐵損，且電路體積取決於磁芯的體積。為了達到高效率以及高功率密度的要求，分數圈繞組的變壓器結構相較於傳統繞組能夠降低輸出電流在繞組上的損耗。藉由各相的二次側繞組同時導通，藉此模擬傳統變壓器結構繞滿一圈的特性。本文利用模擬軟體Maxwell來驗證此變壓器結構以及電路動作的有效性，此變壓器基於LLC串聯諧振轉換器設計。最終成果為功率開關利用氮化鎵晶體，工作頻率操作於1MHz，工作電壓為380V輸入，12V輸出，輸出為1000W之電路，效率最高可以達到97%。

For the high step-down LLC resonant converters with low voltage and high power output, main sources of power losses are copperloss of secondary side and coreloss, also the volume of magnetic component decided total capacity of circuits. Therefore, to achieve high efficiency and high power density, improving the magnetic element is an important issue. The fraction-turns transformer structure can reduce copper length of secondary side, through which can reduce the copper loss of transformer. Therefore, this thesis aims to analyze the availability of fraction-turns transformer structure design based-on LLC resonant converter using Maxwell software. Finally, a 1MHz, 380/12V, 1000W LLC resonant converter using gallium nitride (GaN) devices with a peak efficiency of 97% is achieved.

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