Gapped and un-gapped filter inductor designs for a 500 wrms class-d audio amplifier

The design of a filter inductor for class-D audio amplifiers is investigated, where issues of linearity and bandwidth contribute in addition to losses and size, and inductor modeling is complicated by the combination of high frequency switching and low frequency modulating signals. Two suitable core material types are considered: Gapped ferrite and un-gapped powdered metal, illustrating a trade-off between winding and core losses. The potential for improving semiconductor losses by varying inductance value is also demonstrated. Inductor optimization is illustrated in the design and analysis of a 500 WRMS amplifier inductor. It is shown that the powdered core provides the lowest inductor losses, with improvements of up to 60% over a gapped ferrite design. However the potential for significant amplifier improvement is limited by high semiconductor losses.