Preparation And Magnetic Properties Of Soft Magnetic Powder Core For High-frequency Power Inductor

As the core of the high-frequency power inductor,soft magnetic powder core faces the problem that it is very difficult to optimize the permeability and the core loss simultaneously for single alloy powders.To achieve the balance of different magnetic parameters,the composite powder core prepared with different kinds of powders is usually used.Hereinto,the amorphous powder(AP)with low loss and high frequency stability of the permeability and the carbonyl iron powder(CIP)with high permeability are the most common powders for the preparation of the composite powder core.In this thesis,the AP core,the CIP core and the AP/CIP composite core were prepared through insulating the Fe-Si-Cr-B AP and CIP with the phosphate passivation method and the TEOS hydrolysis method.The effect of the phosphate insulation content on the magnetic properties of the AP and CIP cores,the effect of the TEOS insulation content on the magnetic properties of the AP core and the effects of the mass ratio of the CIP,the compaction pressure and the baking temperature on the magnetic properties of the AP/CIP composite cores were studied systematically.The loss separation fitting was also used to analyze the variation and the determining factor of the core loss.The research findings are listed as follows.(1)Dense insulation layer can be formed on the surface of the magnetic powder by using either the phosphate passivation method or the TEOS hydrolysis method.The problem of sticking the mold for the AP can be resolved by using the TEOS hydrolysis method.(2)The insulation contents of the phosphate and the TEOS influence the core's density directly.The viscosity of the phosphoric acid is helpful for improving the density,but the powder flowability is reduced accordingly which may decrease the density.The silica nanoparticles formed by the TEOS hydrolysis also makes the powder flowability deteriorate and thus results in the decrease of the core's density.(3)The effective demagnetizing field within the powder core determined by the core's density,the magnetocrystalline anisotropy determined by the powder's composition and the demagnetizing field within the magnetic particle determined by the particle's shape and size hinder the magnetization process and thus lead to the decrease of the real part of the permeability,the improvement of the DC-bias performance and the deterioration of the core loss.(4)The core's density also influences the resistivity directly and thus determines the core's eddy-current loss.(5)The AP core possesses low permeability and small high-frequency loss.The CIP core possesses high permeability and large high-frequency loss.The magnetic performance of the AP/CIP composite core is determined by the proportion between these two powders.(6)The magnetic properties of the AP/CIP composite core are also influenced by the compaction pressure and the baking temperature.Small pressure can reduce the eddy-current loss,but the permeability decreases simultaneously.The moderate baking temperature is helpful for softening the resin to achieve the uniform insulation coating which can improve both the permeability and the core loss.(7)The AP/CIP composite core composed of 40 wt.% TEOS-insulated AP powder and 60 wt.% phosphate-insulated CIP powder had a good magnetic performance.The molding choke prepared with this powder core exhibited a high efficiency.