In some researches, the analysis of parasitic capacitances in coils is highly important because the effects of resonance, as in pulse transformers. The obtained system response when its excitation is a square wave shows the existence of parasitic capacitances. In this case, due to the presence of parasitic capacitances, we see that these systems present a resonance based in a sum of responses to step voltage (in each rise and each fall of the square wave), as the frequency of the square wave is increased, as seen in for transformers built with planar coil inner ring coils. But, as the coils are built with coated copper wire, equal effects are presented, although values of these parasitic capacitances may be different because the distribution of turns. In this paper is proposed a formalism to calculate parasitic capacitances on planar coils. This analysis is based on experimental results through RL circuits where the inductor are coils built in a plastic disc with fixed diameter, having the turns disposed elliptically over this disc. The proposed formulation approaches the ellipsis of the turns to circles, and an empirical formula to describe electric potential is obtained, which is used to calculate effective electrical flux and determine the equation that describe the values of parasitic capacitances on these coils.
In this procedure, small errors are verified when comparing to obtained experimental results. The presented approach required the analysis of the effective height between two turns, which is crossed by the electrical flux. This effective height was defined as the ratio of measured and calculated values of the parasitic capacitances, where the result is almost linear. The found errors, comparing the results of found equation with the measured results, are due to low precision on measurements and assembly of coils used in the experiments. However, formulation ensures fast calculation and good approaching.