Research On DC Superposition Characteristic Of Low Losses MnZn Soft Magnetic Ferrite

With the continuous development of electronic technology,MnZn soft ferrite is widely used in various electronic components because of its high permeability,high saturation flux density,and low loss,such as transformers,inductors,choke coils,etc.In order to increase the variation of magnetic flux density B of transformers in power conversion and switch regulation circuits,such as line output transformers,series reactor,pin cusion transformer,etc.it is necessary to superimpose a DC bias field on the magnetic core.The magnetic properties（permeability,loss characteristics,etc.）of soft ferrite will change significantly after superimposing DC bias field,which will affect the stability of the device.In the superimposed DC field,the ferrite core needs excellent electrical and magnetic properties and DC superposition characteristics in order to ensure the stable operation of the device.Therefore,the study of DC superposition characteristics of MnZn soft ferrites is of great significance for its application in electronic devices.This paper is aiming at the demand of excellent magnetic and DC superposition characteristics for ferrite core used in switching power supply.Low core losses Mn Zn soft magnetic ferrites were prepared by solid-state reaction method.The effects of main formula,additives and sintering process on the microscopic,electrical,magnetic properties and DC superposition characteristics of MnZn power ferrites were studied systematically.MnZn soft ferrite materials with high initial permeability,high saturation flux density,and low core losses were developed.Firstly,by the study of Fe₂O₃,ZnO content of the main formula,the influence of Fe₂O₃,ZnO content on instrinsic characteristics of MnZn ferrites was acquired,the optimized main formula is Fe₂O₃:MnO:ZnO=53.2:36.3:10.5 mol%.The results show that appropriate Fe²⁺and Zn²⁺ion substitution could adjust the secondary maximum temperature of initial permeability and saturation magnetic flux density,lower core losses,optimize DC superposition characteristics.Secondly,the effect of ZrO₂,HfO₂ additives on microstructure,electromagnetic properties and DC superposition characteristics of the material was studied.The results show that the addition of 0.01wt%ZrO₂ can effectively improve the microstructure of the material and promote densification.That leads to initial magnetic permeability and saturation flux density increase,and core losses decrease.The addition of 0.09wt%HfO₂ can greatly increase the material resistivity to 34?·m,which leads to the decrease of eddy current loss.At the same time,the microstructure is improved,the magnetic permeability increases and the core losses decrease.Appropriate additives are favorable for obtaining higher incremental magnetic permeability andΔB values,and lower core losses.At the same time,DC superposition characteristics of MnZn soft magnetic ferrite are improved.Last but not least,the effect of sintering process on microstructural and magnetic properties was studied.Appropriate sintering temperature,heating curve and oxygen partial pressure promote the solid-phase reaction,thus promote grain homogenization and densification of materials.Therefore,a process for preparing MnZn ferrite with excellent electric and magnetic properties and DC superimposed characteristics was obtained.