近年來隨著半導體技術及製程之進步， LED之發光效率逐漸提升，加上其具備堅固耐用、使用壽命長以及體積小之優點，使得固態照明取代傳統燈泡成為照明裝置發展之趨勢，但其交流/直流驅動器仍普遍存在效率較低與輸出電流高頻漣波較大等問題尚待進一步改進。

有鑑於此，本文首先提出一具備調光功能以及交流泛用輸入電壓能力之新型單級單開關高降壓比交流/直流轉換器，其電路架構僅需一個主動開關以及一個二極體，如此便可有效降低導通損失，藉此提高效率；另外本新型轉換器藉由設計輸入電容之電容值使其操作於非連續導通電壓模式，如此便可藉由減小輸入電流之零交越點失真角度提高功率因數；同時本文亦藉由使用小電容值之輸入電容以及半共振電路之特性輕易達到高降壓能力，並同時使轉換器具備高電源品質。第二點，本文藉由轉換器理論分析得到其元件參數之設計準則，另外因本新型轉換器係屬高階系統，故本文藉由近似方式推導其電壓增益以及輸入電感電流、諧振電感電流、輸入電容電壓操作於連續與非連續導通模式之邊界條件。第三點，本文更使用低成本之低壓降線性穩壓器IC(AMC 7140)結合本新型轉換器以實現LED之調光控制。最後，本文藉由實際製作一規格為100W、輸入交流電源90Vrms ~ 265Vrms，輸出直流電源24V之實體雛型電路驗證本LED驅動器之可行性與優越性。經實測結果可知於整個交流泛用輸入電源範圍本新型轉換器之功率因數皆高於0.99，而電源轉換效率於輸出功率於20W至120W皆高於90%，同時輸入電流諧波亦均能符合IEC 61000-3-2之規範，最高效率可達92.8%；此外調光範圍可自10%調變至100%，同時輸出電壓漣波亦均能小於平均值之1.54%範圍內。

Due to the advantages of high luminous efficiency, ruggedness, long life and compact size of LEDs, solid state lighting has now become a main trend to replace the traditional lamps. However, the corresponding driver performance such as efficiency and output current ripple remain to be a topic for further improvement.

In this thesis, a novel single-stage single-switch AC/DC converter with universal input and dimming control is first proposed for LED drivers. The new single-stage topology requires only one active switch and one diode to reduce the conduction loss and achieve better efficiency. Also, the input capacitor is designed and operated in the discontinuous voltage mode to achieve unity power factor for an universal input power. Meanwhile, due to the small capacitance value and the quasi-resonance characteristic, the proposed converter can achieve rather high step-down voltage ratio easily. Second, theoretical analysis of the proposed converter is made and some design guidelines are given. Due to high dimension of the proposed converter model, proper approximations are made to derive the voltage gain and the boundaries between continuous conduction mode (CCM) and discontinuous conduction mode (DCM) for input inductor current, resonant inductor current and input capacitor voltage respectively. Third, a low cost low dropout regulator IC (AMC7140) is employed for implementing the dimming control of LEDs. Finally, a prototype with 100W rating, 90Vrms ~ 265Vrms AC input, 24V DC output is constructed to verify the validity of the proposed LED driver. It is seen that the resulting power factor is higher than 0.99, and the efficiency is greater than 90% in the output power range of 20W ~ 120W. Also, the input current harmonics regulation of IEC 61000-3-2 Class C is well satisfied and the maximum efficiency is about 92.8%. The dimming control range is from 10% ~ 100% with an output voltage ripple being less than 1.54%.

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