本論文提出一具前饋機制與無損耗緩振電路之順向返馳型電源轉換器。由於示波器內部類比數位轉換器之位元數限制，造成用交流輸入電源量測電路之共模電壓頻譜顯著的不準確。為了避免量測誤差，使用直流電源量測電路之共模電壓頻譜被提出在本論文中。藉由推導交流和直流電源量測之簡化等效電路，其共模電壓比率可以被計算出，並使用64位元之電路模擬軟體SIMPLIS，驗證所推導之共模電壓比率。然而，使用計算之共模電壓比率來修正用直流電源量測到的共模電壓值，以獲得更準確的等效結果。
　　為符合規範訂定之共模電壓標準，故將變壓器一、二次側間寄生電容降低，但其缺點為漏感值增加。然而，漏感值越大，其儲存的能量越高，將導致電路主開關截止瞬間產生高壓突波，造成開關元件電壓應力上升。因此，於順向返馳型轉換器加入無損耗緩振電路以解決上述缺點。
　　順向返馳型電源轉換器於輸入電壓提高時，輸出電壓漣波會隨之上升，故本論文係利用前饋機制於輸入電壓提高時，調整電路操作頻率，致使輸出電壓漣波降低，以達到規範之標準。
　　最後，實做一7.5瓦特的具前饋機制與無損耗緩振電路之順向返馳型電源轉換器，以驗證本論文所提出之電路特性，諸如降低開關電壓應力、減少共模電壓及減小輸出電壓漣波等。

This thesis presents a modified forward-flyback converter associating with the proposed feed-forward control mechanism and lossless snubber circuit.
　　Due to the digitization error caused by the limited vertical bit number of the analog-to-digital converter (ADC) in oscilloscopes, the CM voltage spectrum measurement of the flyback converter with AC source occurs significant inaccuracy. In order to avoid the digitization error, the CM voltage measurement of the flyback converter with DC source is proposed in this thesis. The simplified equivalent circuits of the flyback converter with AC and DC input sources are derived to calculate the ratio of their CM voltages. With 64-bit circuit simulation software SIMPLIS, the digitization error can be significantly reduced to have high-resolution measurements for the verification of the calculated CM voltage ratio. The ratio of the calculated CM voltages can be used to modify the measurement result with DC source to obtain the equivalent result with AC source.
　　In order to fulfill the common mode voltage requirement of IEC62684 standard, the parasitic capacitor of transformer between primary and secondary sides has to be reduced, which leads to large leakage inductance for the transformer. However, the larger leakage inductance, the more energy stored to cause high voltage spikes on the main power switch during the turn-off transition period. Therefore, the lossless snubber is demanded to suppress the high voltage spikes.
　　Furthermore, the output ripple voltage increases as the input voltage is increased for the forward-flyback converter, which can be improved by employing the feed-forward control mechanism to adjust the switching frequency.
　　Finally, the prototype circuit of a 7.5W forward-flyback power converter is built to verify the performances, such as voltage stress on the power switch, common-mode voltage, output ripple voltage, conversion efficiency, and no-load power consumption.

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