Chester Frank Saj

High efficiency, high density MHz magnetic components for a low profile converter

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. The design of these components is based on a tradeoff study which establishes the optimum operating frequency to be around 1 MHz. The transformer utilizes highly efficient thin flex circuit windings. The windings are novel folded copper patterns, eliminating the need for vias and resulting in very low DC resistance. The winding arrangements have a high degree of interleaving between the primary and 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 introducing a large number (>40) of small gaps to reduce the effect of fringing fields. The high-frequency loss measurements for such highly efficient inductors require a special ring down measurement setup.<<ETX>>

A high-density 1 kW resonant power converter with a transient boost function

A series/parallel resonant DC-DC converter with secondary-side resonance and a novel input boosting feature is described. In order to greatly reduce the conduction loss (factor of 4) due to circulating currents in the resonant components, the boost circuit, which requires no additional active switches, operates only when needed during transient input voltage dips. This reduces the effective input voltage range over which the converter must operate and allows optimization at the steady-state input voltage. The converter employs highly efficient resonant inductors and novel z-folded thin flex circuit transformer windings in order to meet a density of 60 W/in/sup 3/ with an efficiency approaching 95%. The DC-DC converter is being developed for use as a 270 V to 50 V line converter for distributed power applications.<<ETX>>