Current Distribution on Parallel Conductors for Planar Transformers at High Frequency

In high frequency and high current applications, use of parallel winding connection is becoming common practice in planar transformers. However, the current distribution on each parallel conductor is hard to predict. This paper investigates the effect of the insulation thickness and frequency on the current distribution of parallel conductors. When the copper thickness is much larger than the skin depth, the current on each parallel conductor becomes constant. Different layers have varying insulation thicknesses, which is often observed when printed circuit boards (PCB) are fabricated. This also result in unbalanced currents. Based on a 1D model, this paper proposes a methodology for determining the parallel current distribution, specifically used to the N:1 transformer when the copper thickness is much larger than the skin depth. No complex calculation algorithm or simulation software is required. Both finite element analysis (FEA) and theoretical model support the effectiveness of the proposed methodology, which can be used for many parallel structures. The experiment further verifies the theoretical analyses: the current on each parallel conductor is always constant at high frequency; the insulation thickness affects the current distribution.