Research On Planar EMI Filter Based On Circular Integrated LC Component

The traditional EMI filter for switching power supplies, consisting essentially of discrete components, cannot meet the requirements of modern supply on power density. It is imperative to update the traditional discrete EMI filter and reform the integration. Under the existing circumstance, the paper carried on a new planar and integrated EMI filer for modern supply based on the circular integrated LC unit.Firstly, existing modeling technologies of integrated LC component are compared. According to the structural features of circular LC unit, a transmission-line model for high frequency performance based on the generalized arched transmission-line theory is employed. Mathematic models of integrated LC component are derived in two-conductor and multi-conductor structural respectively; the mathematic models of different connection patterns are solved for impedance characteristic and insertion gain, the experimental results verified the correctness of the established model in Matlab. Next, this paper analyzes the influence of structural parameter on the most important parasitic for circular integrated LC component. Meanwhile, an improved lumped circuit model used for design procedures is given.Several issues on designing key parameters for planar EMI filter are discussed in this paper. The integration procedures for CM filter, DM capacitor and DM inductor realized by leakage inductance are introduced in detail, and the design formulas are given, which could offer a basis for the planar integrated magnetic structure of EMI filter. The ways to improve the performance of planar EMI filter are explored; the staggered and interleaved winding structure is studied. Applying these technologies, two integrated EMI filter prototypes are designed and studied. FE simulated results show that EPC can be effectively reduced. However, the price for this is the increased structure complexity and the leakage inductance is also greatly reduced so that additional windings and cores have to be used to realize the DM inductance. In order to cancel the effect of the EPC of CM inductor, an embedded conductive layer is inserted into the CM winding and grounded. The structural capacitance between the embedded layer and CM winding is used to cancel the original EPC of CM inductor. The measurement result confirms that the embedded conductive layer structure is an effective way to achieve the ideal inductance characteristic in high frequency range. The paper analyzes the influence of the parasitic parameters of the inductor and the non-ideal coupling between each other, and the structural parameters of the embedded layer on the EPC cancellation effect. Finally, applying this technology, an integrated EMI filter with EPC cancellation is designed, the comparisons among three different filters implementation are given. The results show that it has a simple structure with much smaller size and profile, and much better CM and DM performance than that of the previous integrated and discrete EMI filters.