交換式電源供應器之電磁干擾濾波器設計方法

A Method for Designing EMI Filters for Switching Power Supply

范振朝(Chen-Chao Fan)

指導教授 ： 范憶華

中原大學/工學院/機械工程學系/碩士(2006年)

https://doi.org/10.6840/cycu200600212

摘要

交換式電源供應器應用提升場效電晶體的交換頻率以減輕電源供應器的體積及重量，但也導致電磁干擾的準位提升，造成一般電器設備電磁相容性降低。本論文即針對交換式電源供應器，以數學方法分析傳導性電磁干擾的特性，設計電磁干擾濾波器，並經實驗驗證其可行性。
針對交換式電源供應器中電磁干擾的問題，近年來，由於測試儀器的進步可以很容易確定電磁干擾的來源，進而減少了利用試誤法求解的不確定性，但存在的問題仍然很多。本研究應用諧振原理提出直接求解二階被動濾波器的共模及差模轉折頻率之方法，並在實務上利用電磁干擾量測系統，從總合雜訊中分離出共模及差模雜訊，並依據雜訊訊號強度判別主雜訊。傳導電磁干擾頻譜可以藉由改變二階濾波器和共模電磁干擾來量測。確認傳導電磁干擾的主來源為何，由總合的傳導電磁干擾頻譜中量測，確認雜訊來源及雜訊來源的特性和研究它的傳播路徑，以更加了解干擾訊號傳導性電磁干擾。並選擇適當之電磁干擾濾波器，以迅速而有效的壓制雜訊，使系統電磁干擾量符合法規之限制。
最後，以24W交換式電源供應器做為待測物，以驗證所提出方法的可行性。根據設計之電磁干擾濾波器實測結果，其電磁干擾分貝微伏特值，均在世界各國傳導性電磁干擾法規限制之下，符合法規限制之要求。

關鍵字

諧振原理 ； 互易定理 ； 傳導性電磁干擾 ； 交換式電源供應器

並列摘要

For designing the switching power supply in miniaturization, the method of increasing the field effect transistor (MOSFET) switching frequency is usually applied. Meanwhile, the electromagnetic interference (EMI) problems are enlarged accordingly, as well as causing the facilities not able to comply with electromagnetic compatibility (EMC) limits. This thesis presents a procedure based on mathematical analysis of conducted EMI characteristics for switching power supply, and proposes a new EMI filter design to be experimentally verified.
To the electromagnetic interference problems of switching power supply, owing to the EMI measurement equipment developed recently, it becomes easier to identify the source of noise. The trial-and-error method has been substituted possibly. As such, numerous problems are still encountered. This thesis proposes the method with applying resonance theorem to solve common-mode and differential-mode corner frequency of the Second-Order passive filter. Practically, uses electromagnetic interference measurement system to separate the common-mode and differential-mode noise from the total conducted EMI, identifies the dominant source of noise with the signal strength. Thus the dominant source of noise can be minimized efficiently. The conducted EMI spectrums are measured by changing the passive filter stages and the common-mode EMI is extracted from the total conducted EMI spectrums in order to identify the dominant source of the conducted EMI. For better understanding of the conducted EMI, the noise sources are identified and the characteristics of the noise source and its propagation paths are investigated from the conducted EMI spectrums measured. Across a proper EMI filter design to attenuate the conducted EMI effectively for the EMC limits compliance.
At last, a 24W switching power supply is used for the equipment under test to verify the feasibility of the proposed scheme. The results of experiment verified the decibel-microvolt of conducted EMI under the worldwide EMC limits as demanded.

並列關鍵字

Switching Power Supply ； Conducted Electromagnetic Interference ； Resonance Theorem ； Reciprocity Theorem

參考文獻

【1】 R. L. Coren, “Reciprocity in EMI-EMC,” IEEE Symposium Record,

International Symposium on Electromagnetic Compatibility, pp.

184-188, 1991.

【2】 T. Guo, D. Y. Chen, and F. C. Lee, “Separation of the common mode

printed structures suitable for controlling EMI noises generated in