Calculation of Planar Transformer Capacitance Based on the Applied Terminal Voltages

Abstract

In order to calculate the parasitic capacitors of a transformer, it is important to apply the correct transformer terminal voltages such that only the desired lumped capacitors are charged. This paper shows the correct transformer terminal voltages that match measurement scenarios that are widely used to extract lumped capacitor values. The parasitic capacitors are calculated based on the stored energy in the transformer windings for different measurement scenarios. A 5kW heavily interleaved high turns-ratio planar transformer is constructed, and its parasitic capacitance is measured. Lumped capacitor simulations are performed using Ansys Maxwell 3D. The simulations are verified through comparison with the measurements and the difference from the measurements is between 1.55-3.76%. The calculation method has a difference of 9.92-10.38% compared to the simulated model, which primarily is caused by an assumption of overlapping turns which is different from the simulated model.