JP3611873B2 - Mn-Zn based ferrite with less power loss in the frequency region of about 100 kHz and method for producing the same - Google Patents

Description

【００２４】
かくして得られた焼結体の、周波数：１００ ｋＨｚ 、最大磁束密度：０．２ Ｔにおける電力損失の温度特性を交流Ｂ−Ｈループトレーサにて測定した。このような測定結果から得られた電力損失の極小値Ｐ_ＣＶとそのときの温度Ｔ_ｐ を表１に併記する。さらに、焼結体を鏡面研磨後、塩酸によりエッチングし、研磨面を光学顕微鏡により撮影した写真から、平均結晶粒径を求めた。
【００２５】
表１から明らかなように、この発明に従い副成分として、酸化けい素、酸化カルシウム、酸化タンタル及び酸化チタンを複合含有させ、平均結晶粒径６〜１５μｍ としたものはいずれも、電力損失は２００ 〜２８９ ｋＷ／ｍ^３ と大幅な低損失を達成している。一方、この発明から外れた組成、平均結晶粒径又は焼結温度では、電力損失が２９０ ｋＷ／ｍ^３ 以上であったり、電力損失が極小となる温度が８０℃以下であるために動作温度近傍で正の温度依存性を持ったりして、実用上問題のあるものであった。
【００２６】
【発明の効果】
かくしてこの発明によれば駆動周波数が１００ ｋＨｚ 程度のスイッチング電源用トランス材料として高磁場下での電力損失が従来の材料と比較して格段に小さい、低損失のＭｎ−Ｚｎ系フェライトを得ることができる。[0001]
[Industrial application fields]
The present invention relates to a Mn—Zn-based ferrite having a small power loss and suitable for use in applications such as a transformer for a switching power supply and a method for producing the same.
[0002]
[Prior art]
Mn-Zn-based ferrite is widely used as a coil and transformer material for various communication devices and power supplies. Especially, it contributes greatly to miniaturization of electronic devices as a transformer material for switching power supplies that operate in a high frequency region of about 100 kHz or higher. Yes. The Mn-Zn ferrite used as a transformer material for such a switching power supply is required to have characteristics such as high saturation magnetic flux density, high magnetic permeability, and low loss. It is important to have low loss below.
[0003]
Various proposals have been made regarding Mn—Zn-based ferrites for switching power supplies at high frequencies. For example, in Japanese Patent Laid-Open No. 3-248405, by adding CaO ₂ , SiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ and TiO ₂ , 25 kHz Although it is said that the loss is reduced in the frequency region of ˜1 MHz, the power loss at 100 kHz and 0.2 T remains at 291 to 338 kW / m ³ .
[0004]
Similarly, JP-A-3-184307 discloses the addition of CaO ₂ , Ta ₂ O ₅ and SiO ₂ , and JP-A 63-62206 and JP-A-5-166620 discloses TiO ₂ and Ta _2. By adding O ₅ , SiO _2, and CaO ₂ , reduction of power loss in a frequency range of several hundred kHz or more, particularly, a high frequency of 500 kHz or more is achieved. However, on the other hand, in the frequency region of about 100 kHz or in a high magnetic field exceeding 0.1 T, the power loss is not improved or even if there is an improvement effect, it is only a poor one.
[0005]
[Problems to be solved by the invention]
In the present invention, the power loss under a high magnetic field is further improved in the standard frequency range of about 100 kHz as the current switching power supply frequency, so that the loss is greatly reduced when used as a transformer for a switching power supply. An object of the present invention is to propose an Mn—Zn ferrite that can be reduced to a low level together with its advantageous manufacturing method.
[0006]
[Means for Solving the Problems]
The Mn-Zn based ferrite of the present invention that solves the above problems is
Fe ₂ O ₃ : 51.5 mol% or more and less than 54.0 mol%,
MnO: 30-39 mol% and ZnO: 8-16 mol%
As a basic component, and silicon oxide as an auxiliary component: 0.005 to 0.015 wt% ( excluding 0.015 wt %) in terms of SiO ₂ ,
Calcium oxide: 0.02-0.15 wt% in terms of CaO
Tantalum oxide: _Ta 2 _{O 5} converted at 0.01 to 0.1 wt% and titanium oxide: TiO ₂ converted at 0.01 to 0.1 wt%
Mn—Zn based ferrite having an average crystal grain size of 6 to 15 μm.
[0007]
Moreover, as the manufacturing method,
Fe ₂ O ₃ : 51.5 mol% or more and less than 54.0 mol%,
MnO: 30-39 mol% and ZnO: 8-16 mol%
As a basic component, and silicon oxide as an auxiliary component: 0.005 to 0.015 wt% ( excluding 0.015 wt %) in terms of SiO ₂ ,
Calcium oxide: 0.02-0.15 wt% in terms of CaO
Tantalum oxide: _Ta 2 _{O 5} converted at 0.01 to 0.1 wt% and titanium oxide: TiO ₂ converted at 0.01 to 0.1 wt%
The Mn-Zn ferrite raw material containing, sintered at 1,300 to 1,370 ° C., it is useful to the average crystal grain size and. 6 to 15 mu m.
[0008]
[Action]
First, the reason why the composition of the basic component is limited to the range of Fe ₂ O ₃ : 51.5 mol% or more and less than 54.0 mol%, MnO 3: 30 to 39 mol%, and ZnO 3: 8 to 16 mol% in the present invention. explain.
[0009]
The operating temperature of the transformer for switching power supply is usually 60 to 70 ° C. Therefore, the Mn—Zn ferrite used in such applications has a small power loss in this temperature range, and the power loss from the room temperature to the temperature range of about 80 to 120 ° C. exceeding the operating temperature has a negative temperature dependence. Is desirable. From this point of view, the inventors examined the preferred composition range of Fe ₂ O ₃ , MnO ₂ and ZnO ₂ , and on the other hand, in the present invention, titanium oxide is contained. Since the temperature characteristic of the magnetic anisotropy constant of ferrite changes, the temperature characteristic of power loss was examined in detail by changing the content of titanium oxide together with the basic component. From these results, each of the above ranges was obtained as a composition suitable for reducing power loss in a frequency region of about 100 kHz and under a high magnetic field of 0.2 T.
[0010]
In the present invention, silicon, calcium, tantalum and titanium oxides are contained as subcomponents in the basic component. The reasons for limiting the contents of these subcomponents are as follows.
[0011]
Silicon oxide: 0.005 to 0.015 wt% in terms of SiO ₂ ( excluding 0.015 wt %)
Silicon oxide increases the specific resistance of the grain boundary by coexistence with calcium oxide and contributes effectively to the reduction of eddy current. However, if the content is less than 0.005 wt%, the addition effect is poor, while the content is the amount is more than 0.015 wt%, when fired at 1300 ° C. or higher, more likely abnormal grain growth occurs and the characteristics are greatly deteriorated, 0.005 to 0.015 wt% (provided that 0. ( Excluding 015 wt %) .
[0012]
Calcium oxide: 0.02-0.15wt% in terms of CaO
Calcium oxide is a useful component that effectively increases the grain boundary resistance in the coexistence with silicon oxide, thereby causing a low loss. However, if the content is less than 0.02 wt%, the effect of improving the grain boundary resistance is achieved. On the other hand, if it exceeds 0.15 wt%, the loss increases conversely, so it was added in the range of 0.02 to 0.15 wt%.
[0013]
Tantalum oxide: _Ta 2 _{O 5} converted at 0.01~0.1 wt%
Tantalum oxide (mainly Ta ₂ O ₅ ) contributes to further reduction of loss in the high frequency region. The reason why the loss is improved by the addition of tantalum oxide has not yet been elucidated, but the high resistance grain boundary phase formed by the combined inclusion of silicon oxide and calcium oxide is altered to increase electrical resistance. This is thought to be due to the effect of mitigating the adverse magnetic effects caused by the presence of a heterogeneous phase at the grain boundaries. However, if the content is less than 0.01 wt%, the effect is poor. On the other hand, if the content exceeds 0.1 wt%, an increase in power loss such as abnormal grain growth occurs at the time of sintering. It was limited to the range of 01 to 0.1 wt%.
[0014]
Titanium oxide: TiO ₂ converted at 0.01 to 0.1 wt%
Titanium oxide (mainly TiO ₂ ) has the effect of promoting re-oxidation of grain boundaries during the cooling process during sintering of the ferrite core, increasing the core electrical resistance, and reducing eddy current loss in the high frequency region. However, if the content is less than 0.01 wt%, the effect of addition is poor. On the other hand, if it exceeds 0.1 wt%, there is an effect of reducing eddy current loss due to high resistance, but at the same time an increase in hysteresis loss is achieved. The power loss that is the sum of these increases. Therefore, it was limited to the range of 0.01 to 0.1 wt%.
[0015]
In the present invention, the average crystal grain size of ferrite is further limited to a range of 6 to 15 μm. When the average crystal grain size is less than 6 μm, the power loss is greatly increased due to an increase in hysteresis loss and when it exceeds 15 μm due to an increase in eddy current loss. For this reason, in the frequency region of about 100 kHz, the power loss is minimized when the average crystal grain size is in the range of 6 to 15 μm. The crystal grain size is defined as follows.
[0016]
That is, after the ferrite sintered body is mirror-polished, it is etched and observed with a microscope to determine the cross-sectional area of the crystal particles. The diameter of a circle having an area equal to the cross-sectional area is defined as the crystal grain size of the particles. The average crystal grain size is obtained by averaging the crystal grain sizes obtained as described above for 500 or more crystal grains.
[0017]
As described above, the present invention achieves the above-mentioned object by containing silicon oxide, calcium oxide, tantalum oxide and titanium oxide, uniformly dispersing at grain boundaries, and setting the average crystal grain size to 6 to 15 μm. It is a thing.
[0018]
In order to produce the ferrite of the present invention, the treatment may be performed according to the following method.
That is, as the raw material, the final composition of the ferrite, for example, 30 to 39 mol% of iron oxide calculated as _Fe 2 _{O 3} is less than 51.5 mol% or more 54.0 mol%, a manganese oxide in terms of MnO, zinc oxide were mixed so as to contain in a proportion ranging from 8 to 16 mol% calculated as ZnO, and then silicon oxide as a sub ingredient (SiO ₂ equivalent) 0.005 to 0.015 wt%, calcium oxide (CaO equivalent) 0.02-0.15 wt%, tantalum oxide (Ta ₂ O ₅ equivalent) 0.01-0.1 wt% and titanium oxide (TiO ₂ equivalent) 0.01-0.1 wt%. What was added so that it may contain is used. However, the addition time of the subcomponent may be after calcination described later.
[0019]
This raw material is calcined at a temperature of 800 ° C. or higher, then finely pulverized, and calcined in a nitrogen gas having a controlled oxygen concentration at a high temperature of 1300 to 1370 ° C.
When the sintering temperature is less than 1300 ° C., the sintering is insufficient, and it takes a long time to grow to the above-mentioned average crystal grain size (6 to 15 μm) of the sintered body. In addition, although the sintering density increases when the temperature exceeds 1370 ° C., an increase in eddy current loss is caused by the occurrence of abnormal grain growth, or residual stress is generated on the surface of the sintered body due to the transpiration of zinc, thereby deteriorating the magnetic properties. . For this reason, sintering temperature shall be the range of 1300-1370 degreeC.
[0020]
In addition, as a raw material of iron oxide, not only Fe ₂ O ₃ but also FeO or Fe ₃ O ₄ , and a compound that can be changed to Fe ₂ O ₃ by firing, such as iron hydroxide and iron oxalate, are used. can do. As the manganese oxide material, not MnO _only, MnO 2, _Mn 3 _{O 4} further compounds which can be changed to MnO by firing can be used, for example, manganese carbonate, manganese oxalate and the like. Furthermore, the zinc oxide raw material is not limited to ZnO 2, and compounds that can be changed to ZnO 2 by firing, such as zinc carbonate and zinc oxalate, can be used.
[0021]
The addition of oxides of silicon, calcium, tantalum and titanium may be in the form of oxides, and also by metals or compounds such as carbonates and oxalates that change to oxides upon heating during the manufacturing process. Good.
[0022]
【Example】
After mixing the raw materials having the basic composition of Fe ₂ O ₃ : 52.5 mol%, MnO ₃ : 36.5 mol% and ZnO 11.0 mol% as the final composition, 900 ° C. for 3 hours in the atmosphere Was calcined. To this calcined powder, SiO ₂ , CaO (using CaCO ₃ ), Ta ₂ O ₅ and TiO ₂ were added and blended so as to be contained at the ratio shown in Table 1 as the final composition, and pulverized with a wet ball mill. Next, PVA (polyvinyl alcohol) was added to the pulverized powder as a binder, granulated, and then formed into a ring shape having an outer diameter of 36 mm, an inner diameter of 24 mm, and a height of 12 mm. This molded body was fired at a sintering temperature shown in Table 1 for 3 hours in a nitrogen atmosphere with a controlled oxygen concentration.
[0023]
[Table 1]

[0024]
The sintered body thus obtained was measured for temperature characteristics of power loss at a frequency of 100 kHz and a maximum magnetic flux density of 0.2 T with an AC B-H loop tracer. The temperature T _p such measurements from a minimum value P _CV obtained power loss at that time are shown in Table 1. Further, the sintered body was mirror-polished, etched with hydrochloric acid, and the average crystal grain size was determined from a photograph of the polished surface taken with an optical microscope.
[0025]
As is apparent from Table 1, according to the present invention, silicon oxide, calcium oxide, tantalum oxide, and titanium oxide are mixedly contained as subcomponents and the average crystal grain size is 6 to 15 μm. A significantly low loss of ˜289 kW / m ³ has been achieved. On the other hand, at a composition, average crystal grain size, or sintering temperature that is out of the present invention, the power loss is 290 kW / m ³ or more, or the temperature at which the power loss is minimized is 80 ° C. or less. In other words, it has a positive temperature dependence and has practical problems.
[0026]
【The invention's effect】
Thus, according to the present invention, as a transformer material for a switching power supply having a driving frequency of about 100 kHz, it is possible to obtain a low-loss Mn—Zn-based ferrite whose power loss under a high magnetic field is much smaller than that of a conventional material. it can.

Claims (2)

Fe ₂ O ₃ : 51.5 mol% or more and less than 54.0 mol%,
MnO: 30-39 mol% and ZnO: 8-16 mol%
As a basic component, and silicon oxide as an auxiliary component: 0.005 to 0.015 wt% ( excluding 0.015 wt %) in terms of SiO ₂ ,
Calcium oxide: 0.02-0.15 wt% in terms of CaO
Tantalum oxide: _Ta 2 _{O 5} converted at 0.01 to 0.1 wt% and titanium oxide: TiO ₂ converted at 0.01 to 0.1 wt%
A Mn-Zn ferrite containing, wherein the average crystal grain size of 6～15Myuemu, 100kHz about Mn-Zn ferrite is less power loss in the frequency domain. Fe ₂ O ₃ : 51.5 mol% or more and less than 54.0 mol%,
MnO: 30-39 mol% and ZnO: 8-16 mol%
As a basic component, and silicon oxide as an auxiliary component: 0.005 to 0.015 wt% ( excluding 0.015 wt %) in terms of SiO ₂ ,
Calcium oxide: 0.02-0.15 wt% in terms of CaO
Tantalum oxide: _Ta 2 _{O 5} converted at 0.01 to 0.1 wt% and titanium oxide: TiO ₂ converted at 0.01 to 0.1 wt%
The Mn-Zn ferrite raw material containing, sintered at 1,300 to 1,370 ° C., characterized by an average crystal grain size and. 6 to 15 mu m, less power loss at 100kHz about the frequency domain Manufacturing method of Mn-Zn ferrite.