JP2688769B2 - High frequency coil - Google Patents

Description

The present invention relates to a high-frequency coil having excellent magnetic characteristics as an inductor of a component of various electronic devices, such as a switching power supply, and particularly to an electrical resistivity in a high-frequency range.
The present invention relates to a high frequency coil using a magnetic core having a large magnetic permeability and a saturated magnetic flux density and a small core loss and having excellent DC superposition characteristics.

[Problems to be solved by conventional technology and invention]

Conventionally, various coils using a magnetic core material having excellent electric / magnetic characteristics such as electric resistivity, magnetic permeability, saturation magnetic flux density and core loss have been used as switching power supply coils for FA equipment and OA equipment. .

However, in recent years, there has been a tendency to use high frequencies in order to improve the characteristics of the equipment, especially downsizing, for example, those that were conventionally used at 10 to 20 KHz or less, but recently, generally 50 to 100 KHz or Higher frequency switching power supplies that have come to be used above this level and have reached megahertz (MHz) are being prototyped.

With the increase in the frequency of such switching power supplies, there has been a demand for high-frequency coils for choke coils that have excellent characteristics in the high-frequency range.

High-frequency coils for switching power supplies currently in use generally have a structure in which a copper wire is wound around a ring-shaped soft magnetic core, and the characteristics of the magnetic core have the greatest effect on the characteristics of the coil. Is giving. As a magnetic core for such a high frequency coil, (1) a ferrite core obtained by sintering a powder of a ferromagnetic oxide having an excellent soft magnetism, and (2) a powder of a ferromagnetic metal having an excellent soft magnetism such as sendust, permalloy and iron. And (3) a wound magnetic core in which a ribbon of a ferromagnetic amorphous alloy having excellent soft magnetism is formed in a toroidal shape.

However, the ferrite core (1) is, for example, 100K
In a high frequency range exceeding Hz, the magnetic permeability is large, but since the saturation magnetic flux density is as small as 5000 G or less, magnetic saturation occurs immediately when a direct current flows through the coil, and the inductance is greatly deteriorated. Since a relatively large DC current flows through the coil in the output side circuit of the switching power supply, the coil used for the switching power supply is required to have a property that the inductance does not decrease even in such a state, that is, the DC superposition characteristic is excellent. So
A high frequency coil having a ferrite core (1) does not have sufficient characteristics for use as a switching power supply.

Next, regarding the core (2), when it is composed of a compacted body of sendust and permalloy powder, the substantial volume ratio (space factor) is as low as about 70%, so the apparent saturation magnetic flux density in the high frequency region is low. Are as low as 7500G and 7000G respectively.
Therefore, the DC superposition characteristic is insufficient. Further, in the case of the iron powder compact compact core, the apparent saturation magnetic flux density of the core is as high as 15000 G or more, so that the DC superposition characteristics are excellent,
Since the electrical resistivity is small and the iron loss in the high frequency range is large, heat loss causes power loss and the inductance is significantly reduced. Therefore, a high frequency coil having a core (2) formed by compacting powder of sendust, permalloy, iron or the like also does not have sufficient characteristics for use in a switching power supply.

Furthermore, since the amorphous ribbon core (3) has a saturation magnetic flux density of 15000 G or more in the high frequency range and a substantial volume ratio (occupancy rate) of 80% or more, the apparent saturation magnetic flux density of the core in the high frequency range is 12000 G. Although it is possible to set the above, since the magnetic permeability is very large, magnetic saturation occurs even when a small amount of direct current flows through the coil, so that there is a problem that the direct current superposition characteristic is low. Therefore, it has been attempted to improve the direct current superposition characteristics by providing an air gap in the magnetic path of the core and increasing the magnetic resistance, but it is difficult to stably provide an appropriate air gap and there is a problem of beating. .
Further, since a Fe-Si-B type amorphous alloy, which is a typical amorphous alloy having a high saturation magnetic flux density, has a large magnetostriction, when a coil having such a magnetic core is used in a high frequency range, electric vibration such as magnetostriction vibration is generated. There is a problem that a beat is caused by. Further, the amorphous alloy material has a problem of high cost.

As described above, a high-frequency coil having a small core loss and a good DC superposition characteristic in a high-frequency range exceeding 100 KHz has not yet been provided.

Therefore, an object of the present invention is to provide a high-frequency coil suitable for use in a switching power supply or the like which has good DC superposition characteristics even in a high frequency range exceeding 100 KHz, has a small temperature rise due to heat generation during use, and can maintain high inductance. Is to provide.

[Means for solving the problem]

As a result of earnest research in view of the above object, the present inventor has found that a coil using a magnetic core material containing Fe-Cr-Al-Si alloy powder having a specific composition as a main component has excellent characteristics in a high frequency range. And found the present invention.

That is, in the high frequency coil of the present invention, at least 60% of the magnetic core material is 1 wt% or more of Al and 1 wt% or more of
Si, 15% by weight or less of Cr, and the balance substantially Fe,
Fe-Cr having a composition in which the sum of Al and Si is 10% by weight or less
It is characterized by being made of powder of -Al-Si alloy.

The Fe-Cr-Al-Si alloy powder preferably has an aspect ratio (maximum length / maximum thickness) of 2 or more and a particle size of 1 to 1.
It is in the form of flakes of 500 μm.

 The present invention will be described in detail below.

The high frequency coil of the present invention comprises at least 60% of the magnetic core material.
Is a powder of Fe-Cr-Al-Cr alloy. This Fe-Cr-Al
-The composition of the Si-based alloy is such that the Al content is 1% or more by weight, the Si content is 1% or more, the total amount of Al and Si is 10% or less, the Cr content is 15% or less, and the balance is substantially. It is Fe.

The additive elements such as Cr, Al, and Si of the above Fe-Cr-Al-Si alloy have the effects of increasing the electrical resistivity of the alloy and improving the soft magnetism. However, if the amount of addition of Cr, Al, Si, etc. is too large, the saturation magnetic flux density will decrease. That is, with Al
If each Si content is less than 1% by weight, there is no effect on improving electrical resistivity and soft magnetism. If the total amount of Al and Si exceeds 10% by weight, or if the Cr content is 15% by weight. When it exceeds, the saturation magnetic flux density decreases. Also, the Cr content is 0.01
If it is less than%, the corrosion resistance is low.

By satisfying the condition of the above composition range, it is possible to obtain a magnetic core having a high saturation magnetic flux density and a high electric resistivity. That is, the saturation magnetic flux density is 13000G or more, preferably 15000G or more, the electrical resistivity is 50μΩ · cm or more, preferably 80
Satisfies the requirement of μΩ · cm or more. By increasing the saturation magnetic flux density, magnetic saturation is less likely to occur even when a relatively large direct current flows through the coil, and it is possible to prevent deterioration of the inductance. That is, the direct current superposition characteristic can be improved. Further, by increasing the electric resistivity, it is possible to reduce iron loss in the high frequency range, prevent the temperature of the coil from rising due to heat generation, and prevent the inductance from deteriorating in the high frequency range.

 The preferable composition of the Fe-Cr-Al-Si alloy is a superimposition standard, Al content: 1 to 7% Si content: 3 to 9% Total amount of Al and Si: 2 to 10% Cr content : 1 to 13% The balance is substantially in the range of Fe.

The powder of the Fe-Cr-Al-Si alloy used in the present invention is flaky (scaly) having an aspect ratio of 2 or more, which is the ratio of the maximum length to the maximum thickness, and a particle size of 1 to 500 μm. preferable. The particle size is determined by measuring the major axis of the powder particles. If the shape is spherical or granular, or if it is flake-like and the particle size is larger than 500 μm, the power loss due to overcurrent of the obtained magnetic core is large, and desired characteristics cannot be obtained in the high frequency range. Further, a coil made of flaky powder having a particle size smaller than 1 μm has a low magnetic permeability.
After all, desired characteristics cannot be obtained in the high frequency range. A more preferable shape is a flake shape having an aspect ratio of 5 or more and a particle size of 10 to 250 μm.

Regarding the powder shape of the Fe-Cr-Al-Si alloy,
From the viewpoint of economy, a small amount may be mixed out of the above range as long as the high frequency characteristics are not impaired.

Such flaky Fe-Cr-Al-Si alloy powder is pulverized or cavitation method disclosed in, for example, JP-A-58-6907, that is, a surface having a small leak property against molten metal is used. A molten metal is supplied to the surface of a roll that has a layer and is rotating at high speed, and the molten metal is divided into fine molten metal droplets, which are subsequently collided with a rotating metal body that rotates at high speed. It can be produced by a cavitation method of causing rapid solidification.

The magnetic core material used in the present invention is 60% by weight or more of the above.
The powder of Fe-Cr-Al-Si alloy is used. If the content of the alloy powder is less than 60% by weight, the effect of the present invention cannot be obtained. In addition, an organic or inorganic binder, other metal powder, or the like can be appropriately used for the rest of the magnetic core material.

The Fe-Cr-Al-Si alloy powder described above in detail is formed into a ring shape to form a magnetic core. Molding can be carried out by an ordinary powder compacting method using a press or the like. By using an organic binder or an inorganic binder such as water glass that is usually used for molding, the moldability can be enhanced and the strength of the magnetic core after molding can be enhanced. Further, the binder enhances the electrical insulation between the particles of the powder, and is effective in improving the high frequency characteristics of the coil. Furthermore, when pressure molding is performed using an inorganic binder, the problem of pressure distortion during molding can be solved, so that the magnetic characteristics of the magnetic core can be improved.

The space factor of the dust core thus obtained is generally 60.
% Or more, preferably 65 or more.

Next, after putting the ring-shaped core in the insulating case,
By winding a copper wire, the high frequency coil of the present invention can be obtained.

An example of the high frequency coil of the present invention is shown in FIGS. 1 (a) and 1 (b). As shown in FIGS. 1 (a) and (b),
The high frequency coil of the present invention has a structure in which a winding 2 is wound around a magnetic core 1. The magnetic core 1 has a structure in which a dust core 1a is covered with an insulating case or a film 1b.

〔Example〕

 The present invention is described in more detail by the following examples.

Reference Example 1 Fe-Cr-Al-Si alloy with Cr content of 3 wt%
The saturation magnetic flux density (Bs) and the electrical resistivity (ρ) of the alloy were measured when the contents of Al and Si were variously changed. The results are shown in FIG.

As is clear from FIG. 2, when Al and Si are each 1% by weight or more and Al + Si is 2 to 10% by weight, the saturation magnetic flux density (Bs) and the electrical resistivity (ρ) are high.

Example 1 Cr 2.7% by weight, Al 2% by weight, Si 6% by weight, balance substantially F
An alloy having the composition e was produced. The saturation magnetic flux density (Bs) of this alloy is 18000G and the electrical resistivity (ρ) is 90μΩ ・
cm. Next, this alloy was pulverized into a flaky powder. The micrograph is shown in FIG. As is clear from FIG. 3, the aspect ratio of the flaky particles is 5 to 5.
The particle size was 100 and the particle size was 20 to 200 μm.

Using water glass as a binder to the obtained powder, 1500
Outer diameter of 20.3m after powder compaction with a press of 0kg / cm ²
A ring-shaped magnetic core having an m, an inner diameter of 12.7 mm, and a height of 6.4 mm was used. The space factor of this magnetic core was 70%. A predetermined insulating case was set on this, and a copper wire with a wire diameter of 1.0 mm was wound with 42 turns to obtain a high frequency coil.

In order to investigate the high frequency characteristics of the obtained high frequency coil, the inductance at 10 KHz, 100 KHz and 1 MHz was measured. The results are shown in Table 1.

Further, the apparent magnetic flux density (B) of the obtained high frequency coil and the inductance (L) under various superimposed DC magnetic fields at 20 KHz were measured. The results are shown in Table 2. The inductance is 0A for the DC superimposed magnetic field.
Relative value (L / L ₀ ) where L ₀ is the inductance at T
Indicated by.

The relationship between the DC superimposed magnetic field in Table 2 and L / L ₀ is shown in the graph of FIG.

At 10KHz and 50KHz, the operating magnetic flux density (△
The power loss of the high frequency coil when B) was 2000 G was measured. The results are shown in Table 3.

Comparative Examples 1 to 4 In the same manner as in Example 1, powders of Sendust (Comparative Example 1), molybdenum permalloy (Comparative Example 2), ferrite (Comparative Example 3), and iron (Comparative Example 4) were used as magnetic core materials. A high frequency coil was obtained.

The apparent saturation magnetic flux density (B) and the inductance (L) of the high frequency coils of Comparative Examples 1 to 3 were measured in the same manner as in Example 1. The results are shown in Table 2 and FIG. The power loss of the high frequency coil of Comparative Example 4 was measured in the same manner as in Example 1. The results are shown in Table 3.

From Tables 2 and 3, the high frequency coil of the present invention is
In particular, it can be seen that the decrease in inductance in the high frequency range of 100 KHz or more is extremely small, the DC superposition characteristics are excellent, and the power loss is small.

〔The invention's effect〕

Since the high-frequency coil of the present invention has at least 60% of its magnetic core material made of Fe--Cr--Al--Si alloy powder having a specific composition, it has a high saturation magnetic flux density and electrical resistivity, and has a DC superposition in a high frequency range. Excellent characteristics and low power loss.

Further, by making the powder of the Fe-Cr-Al-Si alloy into a flake shape having an aspect ratio of 2 or more and a particle size of 1 to 500 µm, the above characteristics can be further improved.

Such a high frequency coil of the present invention can be particularly suitably used as a choke coil for a switching power supply such as OA equipment and FA equipment used in a high frequency range.

[Brief description of the drawings]

1 (a) is a plan view showing an example of the high frequency coil of the present invention, and FIG. 1 (b) is a partially cutaway side view of the high frequency coil shown in FIG. 1 (a). FIG. 3 is a triangular graph showing the relationship between the composition of an example of the Fe—Cr—Al—Si alloy used in the present invention and the saturation magnetic flux density (Bs) and the electrical resistivity (ρ). FIG. FIG. 4 is an electron micrograph (100 times) showing the grain structure of an example of the Fe—Cr—Al—Si alloy used in the invention, and FIG. 4 is a graph showing the relationship between the DC superimposed magnetic field and the inductance (L / L ₀ ). Is. 1 …… Magnetic core 1a …… Dust magnetic core 1b …… Insulation case 2 …… Winding

Claims (2)

(57) [Claims] 1. At least 60% of the magnetic core material comprises 1% by weight or more of Al, 1% by weight or more of Si, and 15% by weight or less of Cr.
The high frequency having excellent DC superposition characteristics, characterized in that the balance consists essentially of Fe, and is composed of Fe-Cr-Al-Si alloy powder having a composition in which the total amount of Al and Si is 10% by weight or less. Coil. 2. The high frequency coil according to claim 1, wherein the powder of the Fe—Cr—Al—Si alloy is flaky having a particle size of 1 to 500 μm and an aspect ratio of 2 or more. And high frequency coil.