Research On Planar Passive Integration Of EMI Filter For Switch Mode Power Supplies

Because of more frequent switching action of SMPS(Switch Mode Power Supplies). EMI (electromagnetic interference) becomes more worsen. To suppress the inducted EMI, EMI filter is used between the power line and the input of converter.However, for conventional discrete EMI filters, its large volume and low space utilization decrease the power density of SMPS; additionally, the parasitic parameters of discrete components worsen the HF (high-frequency) characteristic. To solve these issues and overcome the difficulty of integration capacitances with low relative permittivity dielectric material. A structure of planar passive integrated EMI filter basing on L-C windings stacked-type interleaved connection is proposed in the paper, common mode and differential mode inductors, common mode capacitances and partial differential capacitances are integrated into a planar core with PCB windings and structrue of integrated L-C. On this basis, according to the frequency range of differential mode noise, differential mode capacitance is integrated with X7R. Completely structure of planar integrated EMI filter is achieved. Differential mode and common mode equivalent circuits of high frequency are established, the feasibility and validation are verified by theoretical analysis, simulation and experiments.To improve the characteristic of integrated EMI filter, ESL is eliminated with loop inductance of input and output. Giving approaches to eliminate EPC, analyzing impacts of the coupling coefficient and the embedded ground to eliminate EPC. Finally, carrying out by Pspice simulation.To overcome the difficulty to adjust and achieve differential mode inductances of integrated EMI filter, planar EE core is splited vertically from the center pillar, planar-array integrated EMI filter structure is proposed in this paper. Pointing out advantages of the integrated structure by theoretical analysis and simulation. Finally, analysing the performance stability of integrated EMI filter from characteristics of temperature and frequency of materials, which provide references to select materials for passive integrated EMI filter.