Universal Serial Bus Power Delivery (USB-PD) 協定在近年逐漸成為充電器重要的趨勢，此協定利用微控制器達到充電器二次側與負載的溝通。若利用此微位控制器同時控制一次側主開關，可簡化系統控制並精確量測輸出資訊，因此，二次側控制技術是發展USB-PD重要的關鍵技術之一。本論文提出一新型二次側控制法，使返馳式轉換器操作於定頻零電壓切換。本文所提出之二次側控制法，在主開關導通前，再次導通同步整流開關，以提供反向激磁電感電流，使主開關達到零電壓切換。本論文首先分析返馳式轉換器之動作原理，系統參數設計並討論定頻零電壓切換參數之設計準則。最後，實作一輸入電壓127~373 V、輸出為20 V/5 A之實驗雛形，利用數位訊號處理器TMS320F28335進行控制，以驗證理論分析。此轉換器於此輸入電壓範圍皆可達到定頻零電壓切換，系統最高轉換效率為91.1%。

Universal Serial Bus Power Delivery (USB-PD) protocol has gradually become a trend for adaptor with the micro-controller as the communication protocol between the adaptor output and the load. The secondary-side control was introduced by using the micro-controller as the main controller of the power converter to simplify the system control and modulate output voltage accurately with fast response. In this thesis, a novel secondary-side control is proposed for flyback converter with constant frequency zero-voltage switching. The synchronous rectifier switch is turned on for generating reverse magnetizing current for the main power switch to turn on with zero-voltage switching. The operating principles of flyback converter are analyzed, the system parameters are designed, and the design criteria of the constant frequency zero-voltage-switching are discussed in details. Finally, flyback converter controlled with digital controller TMS320F28335 is implemented to verify the theoretical analysis for 127 V~373 V input range and 20 V/5 A output. The experimental results show that the highest system efficiency is 91.1% with the proposed constant frequency zero-voltage switching.

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