High voltage miniature transformer design

Abstract

This paper presents an example of optimization of a small flyback transformer designed to charge energy storage capacitors up to 2 kV from a low voltage source. The basic design uses a 7 mm diameter by 4 mm high manganese zinc ferrite pot core. Several versions of this transformer were built with different winding patterns. All had similar number of turns and wire sizes. Early versions had Kraft paper insulation between each secondary (high voltage winding) layer. The next version omitted the insulation between the secondary winding layers. As a result, the secondary capacitance of the second version was about three times the value of the first version. From theory, we know that the maximum output voltage is controlled in part by the stray capacitance. The larger the stray capacitance, the smaller the output voltage. Using this starting point, the important outputs, capacitor voltage and charging time, were measured as function of the design control parameters. The design control parameters were the material characteristics, winding pattern, magnetic gap, and turns for primary and secondary. The goal was to minimize the charging time and maximize the output voltage.