Self-Capacitance of Coupled Toroidal Inductors for EMI Filters

This paper presents a derivation of an expression for the self-capacitance of single-layer coupled toroidal inductors, which are commonly used in EMI filters and other applications. A physics-based geometrical method is used in the derivation. This method requires information about the inductor geometry and material properties, such as dimensions of core, technique of winding, as well as diameter, thickness, and permittivity of winding wire isolation. The geometrical method is very useful because it saves time and does not require an impedance analyzer. However, all information about material properties has to be known. The theoretical results are validated by experimental results. The agreement between the calculated and measured results was very good.