在電源系統中，產品規格若能應用於全球的輸入電壓且具備雙組輸出較能滿足使用者方便性的需求。應用上為了達到多組輸出均有良好的穩壓調節率，在設計上有諸多控制方式。本論文所提出之電路是以主輸出組來做回授控制，以獲取穩定的輸出電壓；至於其他各組則由變壓器線圈間的疊接繞組耦合，來得到要求的輸出電壓。
本論文提出一變頻式返馳式轉換器，其控制IC之操作頻率會隨著負載變化，且可操作在不連續導通模式(Discontinuous Conduction Mode, DCM)或連續導通模式(Continuous Conduction Mode, CCM)。操作在輕載時，因切換頻率下降，開關上的切換損耗(Switching Loss)較傳統返馳式轉換器低；當負載越重時，功率電晶體切換頻率隨之增高，且電感電流轉態為連續導通模式，電路操作在此模式下電感峰值電流較小，故此特性使電路在重載時之導通損耗(Conduction Loss)較小。利用變頻控制法，使其操作於不連續導通模式與連續導通模式，這樣的操作方式結合了兩個不同導通模式之優點，也改善其缺點，使電路在寬範圍輸入電壓有更佳的效率表現。

As for power supplies, the specifications of universal input range and dual-outputs are generally appealing to user’s conveniences. In order to achieve the purposes of multiple-outputs and good output voltage regulation, several design approaches can be adopted. The power circuit proposed in this thesis assigns a main output with feedback control to obtain a stable output voltage; while the other outputs is coupled together with cascaded transformer windings to acquire the regulated voltage output.
In addition to the dual-output arrangement, this thesis proposers a variable-frequency control flyback converter. Its control IC is able to adapt its operating frequency according to different load conditions. And the circuit can be operated under discontinuous conduction mode (DCM) or continuous conduction mode (CCM). When the converter is operated at light load, the switching frequency gets lower. The low frequency operation reduces the switching loss. Contrarily, as the load gets heavier, the switching frequency becomes higher and the inductor current turns into CCM. While the flyback converter operates at CCM, the peak inductor current is lower and the conduction loss is smaller, too. The application of frequency-adaption control and toggling operation between DCM and CCM absorbs the advantages and excludes the disadvantages of these two operation modes. These all comes to a result that the flyback converter has a better efficiency with wide input voltage range.

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