Optimal winding design of a pulse transformer considering parasitic capacitance effect to reach best rise time and overshoot

Abstract

High voltage and high frequency pulses are widely used in industrial applications such as klystron modules, radar application, plasma technology, and so on. Transforming such a pulse with magnitude of thousands volt requires special transformers. Considering its frequency requirements which vary from hundreds to thousands Hertz, effects of parasitic capacitance may change the expected results. In this paper a specific method is proposed to optimize the design of both high voltage (HV) and low voltage (LV) windings, to reach the best rise time and overshoot performance. This method is based on both calculations of equivalent circuit and finite element analysis (FEA). Among the various topologies represented in the literatures, cone winding type pulse transformer is selected in which by changing its windings angle, it can be modified to parallel winding type. Initially analytical study in pulse transformer rise time equivalent circuit is performed to find the best cone angle between the windings and also the best distance between the bottom of windings to reach the optimum output parameters of pulse transformer such as fast rise time and minimum overshoot. In this analysis the lumped parameters of the equivalent circuit are calculated based on the stored energy between the windings. Afterwards sensitivity of the response to the load and source parameters variations is calculated in order to find the best distance and the angle between the windings. In the meantime, the distributed parasitic capacitances are extracted by using FEA to exert as circuit elements, in the electromagnetic model of pulse transformer. Finally a transient analysis is executed on the pulse transformer model containing distributed capacitances. The results of this analysis prove that the winding design using the distributed elements effects shows good results considering pulse shape.