The main concern is the first few harmonics of the SMPS switching frequencies in which they may cause EMI non-conformance. Currently SMPS operate anywhere from 100’s of kHz to 2 MHz of switching frequencies. The major concern is the MW-AM band radio (0.52 MHz – 1.73 MHz). In an ideal world, a π-filter provides a perfect solution to EMI generated noise more specifically, for noise reduction due to conducted RF emissions resulting from switched mode power supplies. Suppliers of SMT ferrites provide impedance characteristics vs frequency, and in addition, several lumped circuit models are offered to help the design engineers for the purpose of SPICE simulation. The non-linear behavior is less understood or appreciated, more specifically, when ferrites are utilized on power distribution networks. Nevertheless, an EMI filter design is considered here with components that do deviate from ideal behavior both in linear and non-linear fashion. It is an extremely important aspect of the automotive world for an engineer to get it right in his first attempt. In the cost-effective, high-volume automotive world, it is absolutely essential to avoid EMI failures and reduce design iterations. A product design team must deliver an EMI robust module, which must meet stringent EMI requirements that can be cost-effective, with little opportunity for any design iterations. There are a large number of EMI filter design guidelines and best-practices available to the engineering community. In every product development timeline, engineers seek to find realistic, quick and meaningful solutions. Furthermore, considering the PCB parasitics due to the individual copper traces, or component interaction, can be difficult under a realistic product development budget, if not impossible. However, this can also be limited to provide a solution. In order to gain an insight into the realistic behavior of the EMI filter, one may consider the use of non-ideal electrical models for the filter components. Electrical behavior of an EMI filter mounted on a real product under the influence of complex input/output impedance variation may differ substantially from its basic electrical schematic. Therefore, it is necessary to consider and undertake an experimental approach to identify the ‘technical errors’ which may cause the filter malfunction. It is often considered an art of black magic when a well-designed EMI filter fails to function and deliver any noise reduction, as expected. Ī π-filter that theoretically functions quite well using traditional circuit theory, or simulation tools, may fail to meet the rigor of its practical requirements (CE mitigation). Thus it is a major issue when a non-conformance is achieved with an EMI filter which fails to deliver the required noise mitigation. However, design and PCB implementation of an EMI filter is not an easy task. Discrete π-filters in small foot-print packages are a common design practice by the automotive design community. The use of EMI filters as a noise mitigation technique must be considered carefully as cost and space in highly congested PCBs are two major determining factors. Automotive EMC requirements are more stringent than FCC-15/J Class B limits by at least 54 dB. However, they are inherently noisy and generate ripples that require filters to meet stringent EMC specifications. SMPS have virtually eliminated the use of linear-regulator supplies. Switched mode power supplies (SMPS) are extensively used in automotive electronic modules due to their excellent efficiency. © 2010 IEEE Reprinted, with permission, from 2010 IEEE International Symposium on Electromagnetic Compatibility Proceedings. The PCB implementation of EMI filter is outlined for optimum filter performance. A lumped-element SPICE model is introduced for optimized π-filter design, including frequency-dependent ferrite component model. The power line filters with Surface Mount Technology ferrite and Multi Layer Ceramic Capacitors are attractive solutions for mitigation of RF noise in high-density automotive PCBs. The filter performance is difficult to predict and often compromised at high frequencies due to parasitics associated with the filter itself, or the PCB layout. Electromagnetic interference (EMI) filters are often used on automotive 13.8 VDC power networks to reduce high-frequency noise from being conducted off the printed circuit boards (PCB) and resulting into EMI problems.
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