本論文旨在提出一組雙開關準諧振返馳式轉換器，在傳統返馳式電路加入一上橋開關的設計可以帶來許多好處，尤其是在高壓輸入應用。漏感能量將回收到輸入端，因此不需要外加緩振電路；同時開關電壓被箝制為輸入電壓，將有效地降低元件應力。脈衝寬度調變控制應用準諧振操作，可提升轉換效率。
本論文詳細說明電路動作原理，最後研製一部輸出電壓19 V、額定功率90 W的電源供應器，前級電路使用升壓型邊界導通模式功率因數修正器，為了降低損耗，輕載時進入突發模式工作；後級為雙開關準諧振返馳式轉換器，工作原理類似傳統返馳式電路，並操作在電流不連續模式以實現波谷切換。實驗結果驗證了理論分析的正確性與所研製轉換器之實用性。

This thesis presents a dual-switch quasi-resonant (QR) flyback converter. Compared with the conventional flyback converter, the design with an extra high-side switch brings many benefits, especially in high input voltage applications. The energy of the leakage inductance is recycled back to the input and there is no need for a snubber circuit. As the switch voltage is clamped at the input voltage, the device stress can be effectively reduced. Also the conversion efficiency is improved due to the low switching losses resulted from the PWM quasi-resonant operations.
The operating principles of the presented converter are discussed. A prototype circuit with an output voltage of 19 V and a rated output power of 90 W is implemented. The front stage is a boost-type boundary-conduction-mode (BCM) power factor corrector (PFC), which enters into the burst-mode operation at light load to reduce the switching losses. The second stage is a dual-switch QR flyback converter operated under discontinuous conduction mode (DCM) to fulfill the valley switchings. Experimental results verify the validity of the theoretical analysis and the practicabilily of the studied converter.

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