Fringing-Effect Losses in Inductors by Thermal Modeling and Thermographic Measurements

The fringing-field phenomenon can have a significant impact on power loss and temperature distribution in windings of magnetic components with an air gap. The magnetic flux in a core does not cross the air gap in straight lines, but fringes out into the surrounding medium, causing electromagnetic interactions with the winding enclosing the air gap. The fringing flux induces excess eddy currents in the windings, causing localized heating and reducing the overall efficiency of power conversion. This effect can be analyzed by infrared thermography. In this article, the investigated component is an output choke in a forward converter. Thermographic analysis and power loss measurements were carried out for two different air gap configurations: a single discrete air gap and a quasi-distributed air gap. The obtained thermal characteristics were utilized to construct compact thermal models of the inductor. Compact thermal modeling coupled with thermographic measurements can be used to identify power loss density in individual sections of the copper coil and estimate the impact of the fringing effect on the winding in the vicinity of the air gap. As shown herein, splitting the single air gap into a number of individual air gaps, hence creating a quasi-distributed air gap, causes the fringing effect to be largely diminished.