JPH0544805B2 - - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic core for a high frequency power transformer with low power loss, particularly for a power transformer operating at a high frequency of about 10 to 100 KHz. Prior art and its problems Manganese-zinc ferrite is widely used as a material for coils and transformers in various communications equipment, consumer equipment, etc., but recently there has been a tendency for high frequency power supplies to be used, and it has become difficult to use it for that purpose. There is an increasing demand for performance as a compatible transformer material. Particularly in video decks and various OA equipment, etc., motor drives that use several tens of W of power in the high frequency range of 10KHz to 100KHz, signal amplification,
There is a need for transformer materials that can supply a variety of stable voltages for transmitting purposes, etc. One of the properties required of manganese-zinc ferrite as a transformer material is high magnetic permeability. However, conventional manganese-zinc based high permeability ferrites have large power loss in the high frequency range of about 10 KHz to 100 KHz, and improvements in terms of loss are required. By the way, it is known that the power loss of ordinary transformer/coil materials can be reduced by adding potassium or sodium to manganese-zinc ferrite materials (Japanese Patent Publication No. 1973-
No. 28633). In this case, the amount of potassium and sodium added is K
In terms of conversion, it is less than 0.03wt%. However, the above-mentioned operating frequency of about 10 KHz to 100 KHz causes large power loss and is insufficient for practical use. Purpose of the Invention The present invention was made in view of the above-mentioned circumstances, and its main purpose is to provide a magnetic core for high-frequency power transformers using a novel manganese-zinc ferrite magnetic material with high magnetic permeability and low loss. It is about providing. Such an object is achieved by the following invention. That is, the first invention is a magnetic core for a high frequency power transformer characterized by being made of a manganese-zinc ferrite material containing calcium oxide, silicon oxide, niobium oxide, and sodium oxide. Further, a second invention provides a high frequency power transformer comprising a manganese-zinc ferrite material containing calcium oxide, silicon oxide, niobium oxide, indium oxide and/or bismuth oxide, and sodium oxide. It is a magnetic core for use. Specific Configuration of the Invention The specific configuration of the present invention will be described in detail below. The manganese-zinc ferrite magnetic material in the present invention has iron oxide, manganese oxide and zinc oxide as main components. And these main components are Fe ₂ O ₃
52 to 54 mol% in terms of MnO, 28 to 33 mol% in terms of MnO,
It is estimated to be 13 to 20 mol% in terms of ZnO. Outside this range, the Curie point will be 100°C or less, and μa will decrease in the high frequency region. In this case, it is more preferable that iron oxide is 52.5 to 53.5 mol % in terms of Fe ₂ O ₃ , manganese oxide is 29 to 31.5 mol % in terms of MnO, and zinc oxide is 15 to 18 mol % in terms of ZnO. In addition to these main components, the magnetic material of the present invention contains calcium oxide, silicon oxide, niobium oxide, sodium oxide, and, if necessary, indium oxide and/or bismuth oxide. be done. In this case, the content of each component of calcium oxide, silicon oxide, niobium oxide, and sodium oxide is 0.03 to 0.2 wt% in terms of CaCO ₃ and 0.03 to 0.2 wt% in terms of SiO _2, respectively.
0.001~0.05wt%, 0.001~0.1wt in terms of Nb ₂ O ₅
%, contains less than 0.3wt% in terms of Na ₂ CO ₃ . In addition, the content of indium oxide and/or bismuth oxide added as necessary is 0.001~
It is 0.1wt%. In the ferrite of the present invention, calcium oxide is a component that reduces loss in the high frequency range,
If it becomes less than 0.03wt%, its effectiveness disappears, and
If it exceeds 0.2wt%, the magnetic permeability will decrease. In this case, the calcium oxide content is from 0.04 to
At 0.08wt%, even more favorable results can be obtained. Silicon oxide is also a component that reduces loss in the high frequency range, but if it is less than 0.001 wt%, it becomes ineffective, and if it exceeds 0.05 wt%, the loss increases. In this case, silicon oxide content is 0.008~0.025wt
%, even more favorable results can be obtained. Niobium oxide is also a component that reduces loss in the high frequency range, but if it is less than 0.001 wt%, it becomes ineffective, and if it exceeds 0.10 wt%, the loss increases. In this case, the niobium oxide content is 0.01~0.04wt%
In this case, even more favorable results can be obtained. Furthermore, bismuth oxide is a component that increases magnetic permeability. The magnetic permeability is improved by including bismuth oxide at the above content, but if it is less than 0.001wt%, the effect is lost, and if it exceeds 0.10wt%, the magnetic permeability decreases. I end up. In this case, the bismuth oxide content is 0.01~0.08wt
%, even more favorable results can be obtained. Furthermore, indium oxide also improves magnetic permeability, but its content is 0.10wt% or less, particularly 0.001 to 0.10wt%, more preferably 0.01 to 0.05wt%.
%. These indium oxide and bismuth oxide may be added individually or both may be added. When both are added, the total amount is 0.001~
It is 0.10wt%. Furthermore, sodium oxide also has a loss reducing effect. In this case, the addition of sodium oxide is 0.2wt%
The power loss increases with the addition amount up to 100%, and if it is added more than this, it deteriorates, and if it exceeds 0.3wt%, it is not practical. Moreover, it is not effective at less than 0.001wt%. Further, when the sodium oxide content is 0.09 to 0.24 _wt %, particularly 0.12 to 0.22 wt% in terms of _Na2CO3 , even more favorable results can be obtained. In the ferrite material of the present invention, at 50°C, 25KHz sine wave, 2000G, 70mW/cm ³ or less,
In particular, a low power loss of up to 60 mW/cm ³ can be obtained. A magnetic core for a power transformer made of such a ferrite material operates at a frequency of 10 to 100 KHz, and its power is approximately 10 to 100 W. The shape, dimensions, etc. thereof are known. The ferrite material and magnetic core of the present invention are manufactured according to conventional methods. That is, first, in producing manganese-zinc ferrite, the raw material mixture contains 0.03 to 0.2 wt% of calcium carbonate, 0.001 to 0.05 wt% of silicon oxide, and 0.001 to 0.1 wt% of niobium oxide.
%, sodium carbonate 0.3wt% or less, and if necessary indium oxide and/or bismuth oxide
Add 0.001 to 0.1 wt%, respectively. This is then fired under atmospheric pressure. As the main component in the present invention, a mixture of a usual iron oxide component, manganese oxide component and zinc oxide component is used. These main components each account for 52 to 54 mol% in terms of Fe ₂ O ₃ , especially 52.5 mol%, as the final composition of the magnetic material.
~53.5 mol%, MnO equivalent 28-33 mol%, especially 29
~31.5 mol%, 13~20 mol% in terms of ZnO, especially 15~
They are mixed at a ratio of 18 mol% and used as raw materials. On the other hand, as mentioned above, the raw materials for the trace components contained in the magnetic material of the present invention include calcium carbonate, silicon oxide, niobium oxide, potassium carbonate, and if necessary, indium oxide and/or bismuth oxide. These are added to the raw material mixture. In order to suitably produce a desired magnetic material according to the present invention, first, the main components and additional minor components are mixed, a suitable binder such as polyvinyl alcohol is added in a small amount, for example 0.1 to 1.0 wt %, and molded. Next, this molded product is usually heated at 800~800℃ under atmospheric pressure.
up to a specified temperature within the range of 1000℃, e.g. 300℃/
After rapid heating at a heating rate of about hr, the sample is maintained at that temperature for a certain period of time, preferably one hour or more. Next, in an atmosphere with a controlled oxygen concentration, the material is slowly heated to a desired sintering temperature at a temperature increase rate of 50 to 150° C./hr, and sintering is completed at that temperature. At this time, the firing atmosphere has an oxygen concentration of 1 to 1.
A nitrogen atmosphere controlled to about 15% is preferable. And firing is usually done in this kind of atmosphere.
This is carried out by maintaining a predetermined temperature in the range of 1350 to 1400°C for 1 to 4 hours. The cooling process after sintering is completed in this way is carried out in an atmosphere where the oxygen concentration is controlled according to the temperature from the sintering temperature to about 1200℃, and thereafter in an inert atmosphere, such as a nitrogen atmosphere. is preferred. The cooling rate is preferably about 500 to 700°C/hr. Thus, at a suitable temperature between 800 and 1000℃,
Set a constant temperature state for a predetermined period of time, especially 1 hour or more,
By subsequently performing sintering in an atmosphere with controlled oxygen concentration, extremely high performance characteristics such as high magnetic permeability and low loss in the high frequency range can be obtained. Specific effects of the invention The manganese-zinc ferrite of the present invention has the characteristics of high magnetic permeability and low loss in a relatively high frequency range of 10 KHz to 100 KHz.
It is useful as the magnetic core of a transformer with an output of several watts to several 10 watts for OA equipment, etc. Moreover, such characteristics are realized over a wide temperature range. In this case, as will become clear from the examples below,
When even one essential component of the present invention is missing,
A high loss reduction effect cannot be obtained. Specific Examples of the Invention Hereinafter, specific examples of the present invention will be shown and the present invention will be explained in further detail. Example 1 MnO (30.8 mol%), ZnO (16.4 mol%), Fe ₂ O ₃
(52.8 mol%) as the main component, and as a subsidiary component
_CaCO3 0.055wt%, _SiO2 0.02wt%, _{Nb2O5 0.02wt}
%, _{Na2CO3 is} 0.05wt%, 0.10wt%,
It was added to contain 0.15wt% and 0.20wt%. The firing temperature was 1360°C. 50℃ for this manganese-zinc ferrite
The power loss and μa were measured and shown in Table 1 and Figure 1. Power loss is under the conditions of 25KHz sine wave and 2000G.

[Table] From the results in Table 1, it can be seen that the addition of Na ₂ CO ₃ improves the power loss. Furthermore, when we investigated the change in power loss due to temperature in these ferrite materials, the results shown in FIG. 2 were obtained. From FIG. 2, it can be seen that power loss is significantly reduced over a wide temperature range. Furthermore, in Figures 3, 4, and 5,
Optical micrographs (magnification x 340) of grain growth of ferrite materials in the case of containing 0.05 wt%, 0.10 wt%, and 0.15 wt% of Na ₂ CO ₃ are shown. This shows that the addition of Na ₂ CO ₃ suppresses abnormal grain growth, adjusts the grain size, and contributes to improving magnetic properties. Example 2 For further comparison, MnO (30.8 mol%),
Power loss and power loss were similarly calculated for manganese-zinc ferrite whose main components were ZnO (16.4 mol%) and Fe ₂ O ₃ (52.8 mol%), with the subcomponents changed as shown in Table 2 below, and under the same firing conditions. μa was measured. The results are shown in Table 2.

【table】

[Table] From the results shown in Table 2, the effects of the present invention are clear.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the power loss at 50° C. of the ferrite of Example 1 and the amount of K ₂ CO ₃ added. FIG. 2 is a graph showing the temperature characteristics of power loss and a graph showing the temperature characteristics of magnetic permeability in Example 1. Figure 3 shows Na ₂ CO ₃ 0.05wt of Example 1.
% addition is a grain type photograph taken by an optical microscope. FIG. 4 is a grain type photograph taken with an optical microscope in the case of Example 1 in which 0.10 wt% of Na ₂ CO ₃ was added. Fifth
The figure is a grain type photograph taken with an optical microscope in Example 1 when 0.15 wt% of Na ₂ CO ₃ was added.

Claims (1)

[Scope of Claims] 1. A magnetic core for a high frequency power transformer, characterized in that it is made of a manganese-zinc ferrite material containing calcium oxide, silicon oxide, niobium oxide, and sodium oxide. 2 Calcium oxide content is 0.03 in terms of CaCO ₃
~0.2wt%, silicon oxide content calculated as _SiO2
0.001~0.05wt%, the content of niobium oxide _{is Nb2O5}
The magnetic core for a high frequency power transformer according to claim 1, wherein the content of sodium oxide is 0.001 to 0.1 wt% in terms of _Na2CO3 , and 0.3wt% or less in terms of _Na2CO3 . 3 The content of sodium oxide in terms of Na ₂ CO ₃
The magnetic core for a high frequency power transformer according to claim 1 or 2, which has a content of 0.09 to 0.24 wt%. 4. The magnetic core for a high frequency power transformer according to any one of claims 1 to 3, which has an operating frequency of 10 to 100 KHz. 5. A magnetic core for a high frequency power transformer characterized by being made of a manganese-zinc ferrite material containing calcium oxide, silicon oxide, niobium oxide, indium oxide and/or bismuth oxide, and sodium oxide. 6 Calcium oxide content is 0.03 in terms of CaCO ₃
~0.2wt%, silicon oxide content calculated as _SiO2
0.001~0.05wt%, the content of niobium oxide _{is Nb2O5}
0.001-0.1wt% in terms of indium oxide and/or
Or, the content of bismuth oxide is 0.001 to 0.1 wt% in terms of In ₂ O ₃ and/or Bi ₂ O ₃ , and the content of sodium oxide is 0.3 wt% or less in terms of Na ₂ CO ₃ Claim 5 Magnetic core for high frequency power transformer as described in section. 7 The content of sodium oxide in terms of Na ₂ CO ₃
The magnetic core for a high frequency power transformer according to claim 5 or 6, which has a content of 0.09 to 0.24 wt%. 8. The magnetic core for a high frequency power transformer according to any one of claims 5 to 7, which has an operating frequency of 10 to 100 KHz.