Analysis And Research On Winding Losses Of Magnetic Components In Switching Power Supply

The advent of large-scale integrated circuit (LSI) has prompted the miniaturization of electronic equipments, which calls for the miniaturization of switch-mode power supplies (SMPS). High-frequency magnetic components are the important parts in SMPS, and they take up relative part in size and weight. So it is very important to reduce the size of magnetic components. Increasing the working frequency can reduce the size of the magnetic components, however, the high-frequency effects increase the winding loss. In order to reduce the winding loss, this thesis analyzes the loss in single layer conductor and paralleled conductors caused by high-frequency effect, including skin effect and proximity effect, and proposes a current sharing method for parallel windings of the transformers, and investigates the design for airgap of the inductor.Based on the one-dimensional model of the conductor, this thesis derives the expressions of the loss caused by skin effect and proximity effect by utilizing the orthogonality between skin effect and proximity effect under one-dimensional condition, and analyzes the tendency of the loss in different conductor thickness and at working frequency. It is said that using two thin conductors to replace one thick conductor can reduce the loss resulted by the high-frequency effect. However, with the use of the loss expression, it is found that the loss caused by skin effect is indeed reduced, but the loss caused proximity effect appears, so the total loss keeps unchanged. Furthermore, If the insulation layer is considered, the alternating flux exists in the insulation layers of the parallel conductors will cause loss in the parallel conductors, so the total loss in the thin conductors is even larger than that in a thick conductor. This thesis discusses the relationship between the loss and the layer number of parallel conductors, and indicates that if the overall thickness of parallel conductors is greater than two depths of skin effect, increasing the layer number of parallel conductors can not reduce the loss effectively, and if the overall thickness is greater thanπdepths of skin effect, the loss will be increase slightly when increasing the number of parallel conductors, so it is better to make the overall thickness of parallel conductors around two depths of skin effect in practical application. For low voltage and high current DC/DC converters, in order to enhance the current handling capacity of the windings, it is a very common practice to use parallel windings. Because of high-frequency effects, the current flowing through those windings may be not equal, resulting in high AC resistance. Based on symmetrical structure of winding arrangement and relationship between the resistance and the current in parallel windings, this thesis proposes a winding arrangement method for single secondary winding of transformer, which makes current share in the windings with even number of layers, based on which, a winding arrangement method is proposed for the central tapped transformer. Finite Element Analysis (FEA) and test prove the effectiveness of the proposed methods.Air gap is introduced to the inductor to prevent the core saturation, this thesis discusses the effect on the winding loss of the location of the gap and the arrangement of the distributed air gap. It is indicated that if the air gap locates at corner of core window or near it, the fringing flux can easily enter into the window, which increases the winding loss. In addition, the influence of air gap location to the bypass fluxes are difference for wire winding and foil winding, which results in different influence on winding loss. The location of air gap has no effect on the bypass fluxes in foil winding. For the design of the distributed air gap, if the magnetic columniation between the air gaps is too short, some fringing flux can bypass the magnetic columniation and enter into the window. So letting the magnetic columniation is about 5 times more than the length of little air gap is appropriate. The choice for the number of the distributed air gap is investigated, and the number of the air gap should be ensure that the distance between the windings and air gap is three to five times the length of air gap.