A Method for Designing EMI Filters for Switching Power Supply

• Main Authors: Chen-Chao Fan, 范振朝
• Other Authors: Yi-Hua Fan
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/40514677950339134290

碩士 === 中原大學 === 機械工程研究所 === 94 === 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.