眾所週知的，交換式電能轉換器為EMI(電磁干擾)之主要雜訊來源，必需在輸入電源端，加裝EMI濾波器衰減雜訊的強度，以避免干擾到其它電子設備。然而，此一濾波器雖然達到了符合EMI法規要求，但卻必需付出電能轉換器之體積，重量及成本增加之代價。同時，依照安規規定，為防止使用者觸電之危險，濾波器中X 電容必需加入洩放電阻，此一電阻的損耗，成為功率輸出於51 W以下的電能轉換器，在空載滿足低於0.3 W規範的關鍵因素之一。
本論文藉由應用於交直流轉換器，以降低無負載的損耗為前提下，尋求一同時滿足安規及EMI法規下之電磁干擾濾波器配置。本論文中提出二種方案: (一) 改變橋式整流器之位置及 (二) 使用低於0.1 µF X電容，因此可以符合安規規定將洩放電阻移除，而提出一改良型濾波器之配置。
研究過程，首先依照EMI濾波器之標準設計步驟流程，針對一90W電源轉換器之濾波器進行每一步驟之設計，依照設計步驟及實際量測結果所示本設計可以成功的符合EMI法規之要求。
由實驗結果證明此改良型濾波器之配置在符合安規規定並可通過電磁干擾測試之情形下，可以有效達到洩放電阻之固定功耗消除。
再者，因有效降低共模電感之體積，得以調整差模電感的感量，提高功率密度的性能。

It is well known that the switch mode power supply is the noise source of the electromagnetic interference (EMI). To avoid the interference with the other electronic systems, a filter on the input power source has to be used to attenuate the noise so that the EMI regulations can be met. However, adding an EMI filter as the solution pays the penalty on the converter’s size, weight and cost.
Moreover, there are two series bleed resistors connected in parallel with the X-capacitor within the EMI filter specified by the safety regulation. This resistor power loss is a critical to meet the 0.3 W at no load operating conditions for low power (less than 51 W) applications.
Without violating the safety regulation, two approaches are considered to design the EMI filter without bleed resistors. An improved filter placement is thus proposed and the experimental results are obtained to demonstrate its feasibility.
Following step by step design procedures proposed in the literature, a conventional EMI filter is designed and tested for 90 W AC adapter applications. According to the base-line measurement, higher than 40 dBµV attenuations are required in this application. Therefore, two-stage filter configuration is selected. The experimental results show that the design is successfully met the EMI regulation.
Moreover, several additional advantages are discussed. The proposed EMI filter placement can reduce the size of the CM choke and provide a flexible leakage inductance adjustment for the DM choke. These advantages make the proposed filter placement suitable for high power-density and low-power applications

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