Research On Winding Loss Of High Frequency Planar Transformer

Compared to the conventional wire wound transformer, planar transformer offers many advantages, such as low profile, good thermal characteristic, small leakage inductance and well repeatability, so it is a good solution for high power density and high frequency switch mode power supplises (SMPS).Its research and application are growing in the last decade. However, due to the high switching frequency up to several hundreds kHz, even more than 1MHz, planar transformer is also affected by many high-frequency effects like skin and proximity effects. These high-frequency effects produce ac resistance and leakage inductance that increase the losses of the SMPS, and the performance of the SMPS is reduced significantly. Hence an optimal design of planar transformer should be take into account the high frequency effects.This paper started from Maxwell field equations, thin copper foil the losses caused by skin and proximity effect were studied in the case of one-dimensional. To study the problems of parallel winding layers for high-frequency planar transformer, the Ansoft Maxwell 2D electromagnetic field simulation software was used.The results showed that a simple parallel winding layers arrangement can not reduce the high-frequency losses. Factors affecting the current distribution for parallel winding layers were identified, and the general rules for reducing the unbalance of current distribution among parallel winding layers were presented. At the same time, former vice-planar transformer windings useing interleaving techniques to reduce high-frequency losses in different types of transformers was deeply studied and how to reduced high-frequency losses by interleaving techniques in different types of transformers was analyzed.Then the different interleaving schemes in the condition of high-frequency switching mode were discussed. All the current components including harmonics should be take into account in the interleaving schemes, it's insufficient that only a certain frequency is concidered.Finally fringing effect on high-frequency losses and leakage inductance was analyzed.At last the design process of a flyback converter based on planar transformer is expatiated in detail. According to previous theoretical analysis, three different winding arrangement planar transformers were designed and compared to the wire wound transformer. The experimental result proves that interleaving arrangement of planar transformer has excellent performance and the efficiency of the converter is significantly improved.