Experimental Determination of Stray Capacitances in High Frequency Transformers

This paper presents practical techniques for determining stray capacitances in a two-winding high frequency transformer for circuit simulation and computer-aided design purposes. These techniques fall into two categories: 1) the two-port network approach; 2) the step-response approach. The first approach can be employed for high frequency transformer circuit models with the effect of stray capacitances modeled as a (pi)-shape network of three lumped stray capacitances. The second approach is useful for the transformer circuit model with the overall effects of stray capacitances modeled as lumped stray-capacitance connected cross the primary side. These techniques have been verified in the modeling and numerical simulation of a 500 W 25 kHz two winding E-core transformer. The merits and limitations of these techniques are also discussed.