Impact of the fringing effect on temperature distribution in windings and physical properties of toroidal ferrite inductors with a dual air gap

摘要

This paper examines the impact of the fringing field at an air gap on the temperature distribution, power loss and other properties of toroidal ferrite inductors with a dual air gap. An air gap constitutes a discontinuity in a magnetic path of an inductor, representing significantly greater reluctance to magnetic flux than that of a ferrite core. The magnetic flux does not cross the air gap in straight lines, but fringes out into the surrounding medium causing electromagnetic interactions with the copper winding enclosing the air gap. This phenomenon is a function of the air gap and the windings geometry as well as the operating frequency. The net effect of the fringing flux is to shorten the gap and to decrease the effective reluctance of the magnetic path. Consequently, coils wound on magnetic cores with a relatively large single air gap, thus with an exacerbated fringing effect, exhibit higher inductance than those with multiple, quasi-distributed or distributed air gaps of the same effective length as the discrete one. The presented research investigates the effects of splitting a discrete air gap on the electromagnetic and thermal properties of toroidal ferrite inductors.