Abstract
With the continuous shrinkage of the footprint of inductors and transformers in modern power supplies, higher flux, while still low-loss metallic replacements of traditional ferrite materials are becoming an intriguing alternative. One candidate replacement strategy is based on amorphous CoFeBSi soft-magnetic alloys, in their metallic glass form. Here the structural and magnetic properties of two different families of CoFeBSi-based soft magnetic alloys, prepared by arc-melting and subsequent melt spinning (rapid quenching) are presented, targeting potential applications at effective frequencies of 100 kHz and beyond. The nominal alloy compositions are Co67Fe4B11Si16Mo2 representing commercial Vitrovac and Co72-xFexB28-y (where B includes non-magnetic elements such as Boron, Silicon etc. x varies between 4 and 5 % and y is varied from 0 to 2 %) denoted Alloy #1 and prepared as a possible higher performance alternative, i.e. lower power loss and lower coercivity, to commercial Vitrovac. Room temperature magnetization measurements of the arc-melted alloys reveal that compared to Vitrovac, Alloy #1 already presents a ten-fold decrease in coercivity, with Hc ∼ 1.4 Am-1 and highest figure of merit of (Ms/Hc > 96). Upon melt-spinning the alloys into thin (< 30 μm) ribbons, the alloys are essentially amorphous when analyzed by XRD. Magnetization measurements of the melt-spun ribbons demonstrate that Alloy #1 possesses a coercivity of just 2 Am-1, which represents a significant improvement compared to melt-spun ribbons of Vitrovac (17 Am-1). A set of prototype transformers of approximately 10 turns of Alloy #1 ribbon exhibits systematically Hc < 10 Am-1 at 100 kHz, without a noticeable decrease in coupled flux and saturation.
Highlights
Lower power loss and higher flux replacements for traditional ferrite based inductors are required with the continuous shrinking of inductor footprint
One candidate replacement strategy is based on the amorphous CoFeBSi soft-magnetic systems in their metallic glasses forms
This is enabled by significant advancements by the power semiconductor industry of faster and efficient power switches, as the requirements for smaller and more efficient magnetic components becomes more imminent, at these higher frequencies.[2]
Summary
Lower power loss and higher flux replacements for traditional ferrite based inductors are required with the continuous shrinking of inductor footprint. One candidate replacement strategy is based on the amorphous CoFeBSi soft-magnetic systems in their metallic glasses forms. This is enabled by significant advancements by the power semiconductor industry of faster and efficient power switches, as the requirements for smaller and more efficient magnetic components becomes more imminent, at these higher frequencies.[2] One of the main difficulties in the miniaturization of power conversion circuits is the reduction in size of energy storage and transfer devices, i.e. inductors and transformers.[3] These essential components normally occupy a significant fraction of volume (∼30%) of the power converters. A key roadblock in advancing the passive component technology is the low flux density provided
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