Analysis of Impact of Fringing on Design of Inductors with Air Gaps

Inductors play a crucial role in filtering the harmonic/ripple content generated in the switched-mode power converters. A simple and accurate approach is essential to synthesize inductors of the desired value. Developing a simple magnetic circuit-based approach is easy for synthesizing inductors that are built on high permeability magnetic cores without any air gaps. However, inductors that need to exhibit minimum variations due to operating conditions are often synthesized by using high permeability magnetic cores with air gaps introduced in the magnetic paths. The development of simple approaches for synthesizing inductors with air gaps is a challenge due to the presence of fringing. This paper analyzes the effectiveness of the approaches proposed for computing the inductance in the presence of fringing. Further, a threshold, in terms of air-gap length, beyond which the effect of fringing needs to be considered is computed.