Waseem A. Roshen

Ferrite core loss for power magnetic components design

A practical method is presented for computing high-frequency ferrite core losses in the magnetic component for arbitrary voltage waveforms. The model presented requires only a few material parameters as input. To calculate ferrite hysteresis losses, a model based on empirical rules is employed. For high-frequency eddy current losses, a built phenomenon is assumed. It is demonstrated that the hysteresis model reproduces all of the important known features of the soft ferrites. These features include hysteresis loop shapes for low- and high-field excitations, the nonlinear permeability behavior, and hysteresis loss dependence on the amplitude of the exciting field. It is found that the total calculated core loss as a function of frequency and flux density correctly describes the observed soft ferrite behavior. The theoretical results are compared with available data for two commercial ferrites, and good agreement is found up to fairly high frequencies ( approximately 500 kHz). >

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>>

Megahertz transformers for high density power conversion

Transformer designs that achieve efficiencies greater than 99% operating at 2 MHz at power densities in excess of 400 W/in/sup 3/ for the power range of 50-100 W with output voltages of 1.5 V are discussed. To achieve these results, copper density must be increased beyond what is possible with more conventional Litz wire constructions. Instead, multilayer windings are made of copper foil using flex circuit technology. The elimination of external connections between the winding layers by incorporating the interconnections as an integral part of the winding design is described. This results in Z-folded winding structures that can be ultimately interleaved to achieve high copper density, low copper loss, and very low leakage inductance. >

High density interconnect embedded magnetics for integrated power

We introduce here a new transformer/inductor technology which is suitable for integrated power for multichip modules (MCM), microprocessors and chip sets. The transformer/inductor is embedded within the ceramic substrate, as are the chips and other components. It provides for extremely tight secondary side circuit layouts with very low and fixed leakage inductance. The core is a new multipole structure which can be considered as a number of transformers integrated into one monolithic structure. The core consists of a bottom ferrite plate, and the winding is constructed using high density interconnect techniques (HDI), such as laminating dielectric layers and depositing winding metals using sputtering followed by electroplating.Winding patterns are etched using photo-resist and wet etching techniques. Multiple vias are used to connect different primary and secondary winding layers. A conformal metal mask is used to laser-drill through (large) holes for the posts of the top part of the core. An experimental 50-W, six-pole transformer has been built using these techniques. It operates at 1.0 MHz with efficiency approaching 98.7% and has a net height of about 0.09 in (∼ 2.3 mm). It has a power density of 71 W/cc (or 1170 W/in3) and a surface power density of 17 W/cm2.

MHz transformers for high density power conversion

The authors discuss transformer designs that achieve efficiencies greater than 99% operating at 2 MHz at power densities in excess of 400 W/in/sup 3/ for the power range of 50 to 100 W with output voltages of 1.5 V. To achieve these results copper density must be increased beyond that possible with more conventional Litz wire constructions. Instead, multilayer windings are made of copper foil using flex-circuit technology. A particular innovation described is the elimination of external connections between the winding layers by incorporating the interconnections as an integral part of the winding design. This results in Z-folded winding structures that can be intimately interleaved to achieve high copper density, low copper loss, and very low leakage inductance.<<ETX>>