Nailing Common Misunderstandings about EMI Filters
Despite EMC issues now usually being considered at an early stage during the product design process, unexpected problems still occur. In some cases, a simple approach to EMC and filtering is found to work but, more often than not, a more in-depth analysis is required to address the relevant EMC design considerations and subsequently identify the EMC solution. Misunderstandings are prevalent when selecting EMI filters in the course of equipment design, and here we explore some of the more common ones.
Filters will give their full quoted performance up to their full rated current. For instance, 30A filters will give full performance where used at a lower, 20A, current. The chief exception is for single-line filter designs where the magnetic core will progressively saturate and give lower inductance and lower performance as load current increases. A reputable filter manufacturer should allow for this and quote performance figures based on the worst case, full load condition.