High-efficiency, high-density MHz magnetic components for low profile converters

A highly efficient (99.5%) transformer and resonant inductor with very high power density (1500 W/in/sup 3/) and low profile (height <0.4 in) are described. These may be the highest numbers for power density for 99.5% efficient magnetic components. The design of these components is based on a trade-off study which establishes the optimum operating frequency to be around 1 MHz. The results of this trade-off study which established the baseline designs including the sizes are described. The transformer utilizes highly efficient thin flex circuit windings. The windings are novel folded copper patterns which eliminate the need for vias and results in very low DC resistance. The windings' arrangements have a high degree of interleaving between the primary and the secondary windings, resulting in very low AC conductor losses due to skin and proximity effect. The core is a low profile design with very low core losses. The resonant inductor, instead of using low permeability material, uses highly efficient high permeability material. The desired low permeability is then achieved by putting a large number (>40) of small gaps to reduce the effect of fringing fields. The high-frequency loss measurements for such highly efficient inductors requires a special ring down measurement set-up which is also described.<
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