本論文提出一新型高降壓直流對直流轉換器，透過整合主動箝位電路，使得本轉換器主動開關不需要操作至臨界工作週期及可達到高降壓且具柔性切換之特性，進而使得本論文所提之轉換器可達到高效率之優點。本文首先說明所提轉換器之工作原理，而後針對其完成穩態分析，透過穩態分析結果可進一步完成電路參數設計。最後，研製一輸入電壓400V，輸出電壓為24V，輸出功率200W之電路雛型，並由實驗結果驗證理論分析之可行性。由實驗結果可得，本文所研製之雛型硬體電路於輸出功率80W條件下可達到最高效率95.25%。

In this thesis, a high step-down DC-DC forward converter with active clamp circuits is proposed. By integrating two active clamp circuits into the proposed converter, the high step-down capability and soft-switching feature can be achieved without using extreme duty cycle of the active switch so that the conversion efficiency of the proposed converter can be further enhanced. In this thesis, the operation principle of the proposed converter is first addressed. Then, the steady-state analysis is presented. According to the derived equations of the steady-state analysis, one can further design the circuit parameters in hardware implementation. Finally, a laboratory prototype with 400V input voltage, 24V output voltage, and 200W output power rating is implemented to verify the validity of the proposed converter. The experimental results of the constructed converter prototype show that the highest of 95.25% can be achieved at the 80W output load condition.

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