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In today's high-frequency low-profile switching-mode power converters, paralleling winding in planar transformers is needed, especially for low voltage and high current applications. Although this practice is believed to be effective to increase the current handling capacity of the windings, the effect might be offset due to the unequal current sharing within parallel layers if the winding layers are not properly arranged and connected. In this work, the particular problems raised from parallel winding are addressed and modeled based on a one-dimensional field model. The factors affecting winding losses with parallel connection are analyzed. Software to predict the current density distribution and AC loss for planar windings has been developed.