Design Of Integrated EMI Filter Based On Flexible Multi-layer Foil

Serious EMI (electromagnetic interference) is caused while the switch is turned on or off in SMPS (switching model power supply). To suppress inducted EMI, EMI filter is used. However, for traditional EMI filter, its low space utilization decreases the power density of SMPS, and its HF (high frequency) property is bad because of parasitic parameters. To reduce the volume of the filter and side effects of parasitic on HF property, passive integration structures were proposed based on FML foil (flexible multi-layer foil).The inductor equivalent parallel capacitance (EPC) worsens the characteristics of integrated EMI filter at high frequency. This paper derived the formula of EPC based on the principle of capacitor energy storage, modified the equivalent models of integrated filter and proposed methods to reduce EPC.To reduce volume, 5 integrated structures were proposed, which integrated DM (differential model) inductors, CM inductors and DM capacitors, while CM capacitors were discrete components. The DM windings are designed to increase DM insert loss. The integrated principles were detailed and characteristics were analyzed for the 5 integrated structures. A prototype was made for the most compact structure. Its insert losses were analyzed, the testing EMI results and efficiency were given, and its volume was compared with traditional EMI filter.4 complete integrated structures were proposed, which integrated all the passive components of the filter in one core. The integrated principles and insert losses were analyzed, the testing EMI results and efficiency were given, and its volume was compared with traditional EMI filter.