交流/直流轉換器被廣泛使用於現代各式各樣的電子產品,如LED電源驅動器、電池充電器、個人電腦及家電用品等等。在電源設計領域，不同的技術被研發及提出，皆為了獲得更低成本及更高的性能以贏得市場的競争性。在本論文中，提出一個嶄新單級單開關交流/直流轉換器的模型並加以實現，相較於已知同類作法，具有高功率因數、高效率、低諧波電流、更小尺寸及更低成本的特性。本論文對提出的電路模型的工作原理、穩態分析、設計考量準則、模擬分析、電路雛型及實作結果，本論文均加以詳細說明。
所提出的轉換器模型，適用於輸入工作電源在110VAC 60Hz、輸出負載在20W至50W範圍內，它的低頻諧波成份符合國際標準規範IEC 61000-3-2要求，相較於同類己知的方法具有以下四個優點：
1. 功因修正部份所使用的電感器，由一組變壓器輔助繞組所取代，可減少磁性材料的總體積及重量，因此可降低成本。
2. 直流匯流排大電容器上的電壓，可被箝位在輸入電源整流後的電壓之下，且不受負載的變動影響。直流滙流排大電容及功率半導體元件選擇低耐壓的元件即可，因此亦可降低材料成本。
3. 工作效率介於89%至90%之間。
4. 功率因數介於0.94至0.95之間。

AC/DC converters are widespread used in modern electronic products, such as LED power drivers, battery chargers, personal computers and household appliances. While pursuing the lower cost and higher performance, various techniques have been developed and proposed to raise market competency. We propose a novel single-stage single-switch AC/DC converter based on the flyback topology with the characteristics of high power factor correction, high efficiency, low harmonic current, smaller size and lower cost. The topology evolution, circuit operation principles, steady state analysis, design guidelines, simulations, a prototype and experimental results of the proposed converter are presented. The feasibility of the proposed converter is thus demonstrated.
This proposed converter complies with the standard IEC 61000-3-2 for low frequency harmonics under a output power range of 20W to 50W at the input rating of 110VAC 60Hz. As compared with related known approaches, it has four major advantages:
1. The bulk inductor for power factor correction is replaced by the proposed auxiliary winding of the transformer to reduce the volume and weight of the magnetic material used, which reduces costs.
2. The voltage of the DC-bus bulk capacitor is clamped under the rectified line voltage and not influenced by the output load variation. Hence, the requirements for sustained voltage stress of both the DC-bus capacitor and power semiconductor device are less as compared with previous approaches. That also implies lower cost and higher power density.
3. The working efficiency is between 89% and 90%.
4. The power factor is between 0.94 and 0.95.

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