本論文提出一市電頻率並串聯自動切換發光二極體驅動電路，再依此架構，發展出雙輸入電壓準位發光二極體驅動電路及填谷式發光二極體驅動電路。本驅動電路所採用之並串聯自動切換機制是以輸入電壓為控制訊號，隨著輸入電壓的上升，兩串發光二極體之接法由並聯自動切換為串聯。因發光二極體的導通數目在低輸入電壓值時減半，故能增加順向導通時間，進而提高功率因數及降低峰值因數。為了使驅動電路之輸入電壓方均根值具110 V/220 V兼容性，故於所提出之驅動電路中加入雙輸入電壓準位機制。另外，亦將所提出之驅動電路應用於填谷電路中，以改善光閃爍問題。最後，本論文實際研製雙輸入電壓準位發光二極體驅動電路及填谷式發光二極體驅動電路，以驗證本論文所提出之電路特性，諸如功率因數、峰值因數、雙輸入電壓及光閃爍現象之減緩。

In this thesis, a line-frequency parallel/series automatic switching LED driver is proposed. Based on the topology of the parallel/series automatic switching LED driver, a dual input-voltage-level LED driver and a valley-fill LED driver are further presented. The parallel/series automatic switching mechanism employed in the proposed LED driver utilizes the input voltage as the control signal. With the increasing of the input voltage, the connection of two LED strings automatically changes from parallel to series. Since the number of the turned-on LEDs is reduced by half with low input voltage value, the forward-conduction time for LEDs is increased, which further improves power factor (PF) and crest factor (CF). For the purpose of compatibility with the RMS input voltages of 110 V and 220 V, the dual input-voltage-level mechanism is added into the proposed LED driver. Moreover, the proposed LED driver can be applied with a valley-fill circuit in order to improve the flicker problem. Finally, two prototype circuits of dual input-voltage-level LED driver and valley-fill LED driver are built to verify the performances, such as PF, CF, dual input voltage, and the improvement in flicker problem.

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