JP2000182845A - Composite core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high inductance and a low loss for a bias current by specifying the volume percentage of a powder B to the volume sum of a powder A and the powder B as a compound ratio of the powder A to the powder B, wherein the mode of the grain size distribution of the powder A is a specified multiple of that of the powder B. SOLUTION: A bulk core uses a ferrite material, i.e., Ni-Zn ferrite and has a U-shaped core, heat-resistive tape is wound around the core 1 to form a slurry injection type convenient mold, a coil 3 is adhered and fixed to the center of the core 1, a soft magnetic powder-mixed slurry 2 is injected in the convenient mold made from the heat-resistive tape and hardened, and then the tape of this mold is removed to obtain a composite core 4. Powders A, B of the slurry 2 are compounded so that the volume percentage of the powder B to the volume sum of both powders is 15-60% and the mode of the grain size distribution of the powder A is 5 times or more that of the powder B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an inductance element such as a choke coil and a transformer mounted on an electronic circuit.

[0002]

2. Description of the Related Art At present, ferrite is mainly used as a core material of an inductance element such as a transformer or a choke coil. Ferrite is a highly versatile magnetic material that has excellent moldability and workability, is inexpensive, and can be used up to high frequencies in terms of magnetic properties, and has characteristics such as low loss and high magnetic permeability.

[0003] As another soft magnetic material, there is a dust core using a metal soft magnetic material powder. Although this dust core is superior to the ferrite in terms of high saturation magnetic flux density and stability of the temperature characteristics of magnetic permeability, it has a problem that the molding pressure is remarkably high, and thus the produced shape is limited.

[0004]

An inductance element such as a transformer or a choke coil using a ferrite uses a magnetic path to prevent magnetic saturation due to a bias current flowing through a coil in which a ferrite core is wound around the inductance element. Although a gap is provided in the portion, the characteristics as a ferrite material are impaired by the gap. Particularly, an increase in loss and a leakage magnetic flux have been problems.

A dust core using a metal-based soft magnetic material powder hardly causes magnetic saturation with respect to a bias current without providing a gap in a part of a magnetic path, and has a small leakage magnetic flux. There is a problem that the number of turns of the coil is increased to obtain a required inductance value due to low magnetic permeability. The present invention provides a magnetic core for an inductance element that solves the above problems.

[0006]

According to the present invention, a solid bulk soft magnetic material is used as a part of a magnetic path of a composite magnetic core, and the remaining magnetic path is formed by bonding a powder of the soft magnetic material with a liquid resin. This is carried out using a powdered resin hardened magnetic core which is obtained by mixing materials and forming a slurry, or by mixing a resin with a soft magnetic material powder and heating and once liquefied. The powder constituting the powdered resin cured core is composed of powder A and powder B of a soft magnetic material, the mode of the particle size distribution of powder A is at least 5 times that of powder B, and powder A and powder As a compounding ratio of B, the volume percentage of the powder B to the total sum of the volumes of the powder A and the powder B is 15% or more and 60% or less.

[0007] The solid bulk core used here is a conventional ferrite core or Fe-Al-Si.
A dust core formed by pressing a magnetic powder such as an alloy is used.

[0008] The composition of the soft magnetic material powders A and B, which become liquid once the resin is added, is basically not limited.
Metal powder such as e-Al-Si alloy, permalloy, silicon iron, pure iron, amorphous alloy, microcrystalline alloy, or metal oxide powder such as ferrite can be used.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a magnetic core of an inductance element such as a transformer or a choke coil, wherein a composite magnetic core composed of a solid bulk magnetic core and a powdered resin cured magnetic core is used. The required magnetic characteristics can be obtained depending on the ratio occupied by two magnetic cores. The powdered resin cured core is in contact with the bulk core in the form of a slurry with respect to the bulk core, and is tightly fixed to the bulk core when the slurry is cured.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment according to the present invention will be described below.
In this embodiment, Ni-Z is used as the bulk soft magnetic material.
An n-type ferrite was used. The powdered resin cured core to be combined with the ferrite is Fe-Al-S as powder A.
A water atomized coarse powder having an i-alloy composition was pulverized with a dry ball mill and a water atomized fine powder having an Fe-Al-Si alloy composition was used as powder B. Powder A was annealed at 950 ° C. in hydrogen after grinding, and its particle size distribution is shown in FIG. The particle size distribution was measured by a laser scattering method. The mode of the particle size of this powder is in the rank of 44 to 62 μm, and the median value of 53 μm is the mode of the powder A. (Hereinafter, the mode of particle size of each powder was calculated by this method). Powder B
Is used as it is after water atomization and dried,
FIG. 2 shows the particle size distribution. The mode is 5.5-7.8μ
m, and the median value of 6.7 μm is the mode of powder B. The mode ratio of powders A and B is 7.9. Solvent-free varnish (styrene polymerized unsaturated polyester type) was used as a binder.

The above-mentioned varnish is added little by little to a mixture obtained by putting predetermined amounts of powder A and powder B in a mortar and stirring, and the varnish is added until the mixture becomes a slurry and starts to flow. The addition weight was recorded. After vacuum defoaming the slurry for 5 minutes, the slurry was poured into a 26 mm outer diameter toroidal plastic case at 120 ° C.
Heat curing was performed for 3 hours. The inner volume of the case has an outer diameter of 24φ, an inner diameter of 13.5φ, and a height of 6.6H (mm). The slurry density was calculated from the weight of the injected slurry and the volume in the case, and the space factor of the magnetic core was calculated from the powder weight, the added amount of the resin, and the true density of the Fe-Al-Si alloy.

The magnetic properties to be measured were measured by measuring the magnetic permeability μi at 100 kHz with an LCR meter by winding a wire around the toroidal magnetic core. The core loss Pcv at 100 kHz and 50 mT was measured by a BH analyzer.
Was measured. The sum of the saturation flux densities of the individual magnetic materials multiplied by the volume percentage was defined as the composite saturation magnetic flux density, and the product of the occupation rate and the sum was regarded as the composite saturation magnetic flux density Bs of the obtained magnetic core.

Next, in order to confirm the magnetic characteristics in the actual shape, a composite magnetic core combining the above slurry and a ferrite core was prepared in the following manner. The ferrite material used for the bulk core is Ni-Zn based ferrite (Hitachi Metals)
(NL30S manufactured by KK Corporation), and the magnetic core shape was a U-shaped magnetic core 1 shown in FIG. After winding a heat-resistant tape having a width of 5 mm around the outer periphery of the magnetic core 1 to make a simple type of slurry injection, 1UE
W, a coil 3 formed by winding a self-fusing wire of 0.3 mm in diameter for 30 Ts, is adhered and fixed to the center of the ferrite core 1, and the slurry is poured into a simple mold made of heat-resistant tape up to the upper end of the tape. Slurry 2 at 120 ° C for 3 hours
Was cured. After curing, after removing the simple type tape, a composite magnetic core 4 having an outer dimension of 15 × 8 × 5 (mm) is obtained. FIG. 4 is a sectional view of the composite magnetic core.

In the above-mentioned composite magnetic core 4, powder A and powder B
Table 1 also shows a comparison table of magnetic properties when the compounding ratio of was changed, and also shows a magnetic property when a toroidal core was used. As a conventional example, an outer diameter of 24
φ, inner diameter 13.5φ, height 6.6H (mm), toroidal core, and EI shown in FIG.
Core (E-shaped core 5 and flat plate core 6 having an elliptical middle leg,
The data of a toroidal core having the same shape as the above-described present invention example, which is made of a Fe—Al—Si powder magnetic core manufactured by normal pressure molding, is shown.

[0015]

[Table 1]

When the mixing ratio of the powder B is 45 vol%, the space factor and μi are maximum as toroidal core characteristics,
This is significantly improved as compared with the case of a single core of each of powders A and B.

Also, regarding the composite magnetic core characteristics, the volume percentage of the powder B with respect to the total volume of the powders A and B is 1%.
In the region of 5% or more and 60% or less, both the inductance and the core loss are remarkably improved as compared with the case where the magnetic core is constituted only by ferrite.

As a second embodiment of the present invention, the magnetic characteristics of the composite magnetic core according to the present invention were confirmed by the ratio of the magnetic path length of the cured resin core to the total magnetic path length. As each magnetic material used in this example, the Ni-Zn-based ferrite used in the first example, powder A and powder B, and a slurry obtained by stirring a binder were used. In addition, the slurry was powder A: 55 v
ol%, powder B: 45 vol%.

The shape of the composite magnetic core is EI shown in FIG.
The coils used in the first embodiment were arranged on the respective ferrite cores shown in FIG. 6 with mold core dimensions, and the above-mentioned slurry was cast and cured to produce an inductance element using a composite magnetic core. FIG. 7 shows a sectional view of each inductance element. (2-a) to (2-e) are obtained by combining a powdered resin cured core with each of the ferrite cores in FIG. As a conventional example, a magnetic core was composed only of the powdered resin cured magnetic core of (2-f), and a magnetic core composed of only the ferrite core of (2-g) was also measured. The middle leg of the E-type ferrite core 7d shown in FIGS. 6 and 7 is provided with a gap of 0.45 mm.

Table 2 shows the characteristics obtained in the above experiment.
The value of (powder resin cured magnetic core magnetic path length) / (total magnetic path length) is 2 to 3.
In the 80% region, both the inductance and the iron loss are remarkably improved as compared with the magnetic core (2-g) of ferrite alone. In addition, since a part of the magnetic path is made of ferrite having high magnetic permeability, the inductance is remarkably improved as compared with the case of the powder molded core alone (2-f). FIG. 8 shows the DC superposition characteristics of each sample. Even when the bias current is increased in the configuration of the sample (2-b), the sample exhibits high inductance, has well-balanced characteristics, and is suitable as a current smoothing choke coil.

[0021]

[Table 2]

In general, the characteristics of the inductance element are largely controlled by the magnetic characteristics of the soft magnetic material in the portion (the middle leg portion in the above embodiment) surrounded by the coil. In particular, in applications where magnetic saturation is a problem such as a choke coil, It is desirable to use a metallic material having a high saturation magnetic flux density for the center leg of the magnetic core.

FIG. 9 shows an example of the shape of a bulk magnetic core used in the composite magnetic core of the present invention. In the embodiment, the EI
Although the ferrite core of the mold is used, the tape for holding the slurry can be made unnecessary by using the box-shaped core 8 shown in FIG.
The choke coil can be formed by fixing it inside, injecting and curing the slurry.

[0024]

According to the composite magnetic core of the present invention, since a part of the magnetic path is constituted by a powdered resin hardened core formed by hardening and molding a slurry obtained by mixing soft magnetic powders A and B, a bias current can be reduced. It is possible to use a slurry obtained by mixing the soft magnetic powders A and B with a ferrite core that enables high inductance and low loss, and further has good moldability and workability.
Various shapes can be manufactured.

[Brief description of the drawings]

FIG. 1 is a particle size distribution diagram of a soft magnetic powder A used in an example of a composite magnetic core of the present invention.

FIG. 2 is a particle size distribution diagram of a soft magnetic powder B used in an example of the composite magnetic core of the present invention.

FIG. 3 is an external view of a ferrite core used in the first embodiment of the composite core of the present invention.

FIG. 4 is a sectional view of an inductance element according to a first embodiment of the composite magnetic core of the present invention.

FIG. 5 is an external view of a conventional magnetic core.

FIG. 6 is an external view of the shape of a ferrite core used in a second embodiment of the composite core of the present invention.

FIG. 7 is a sectional view of an inductance element according to a second embodiment of the composite magnetic core of the present invention.

FIG. 8 is a diagram showing a DC superposition characteristic of an inductance element according to a second embodiment of the composite magnetic core of the present invention.

FIG. 9 is a perspective view showing an example of the shape of a bulk magnetic core used in the composite magnetic core of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 bulk core 2 powder resin cured core 3 coil 4 composite core

Claims (3)

[Claims] In a composite magnetic core formed by combining a plurality of soft magnetic materials, a bulk soft magnetic material is used as a magnetic material forming a part of the magnetic path, and the remaining part of the magnetic path is formed. As the soft magnetic material, a powder resin cured core formed by mixing two kinds of soft magnetic material powders A and B having different particle diameters and a liquid binder to form a slurry, and then curing the binder is used. The mode of the particle size distribution of the powder A is at least 5 times that of the powder B, and the mixing ratio of the powder A and the powder B is the volume of the powder B with respect to the sum of the volumes of the powder A and the powder B. A composite magnetic core having a percentage of 15% or more and 60% or less. 2. The composite magnetic core according to claim 1, wherein the magnetic path length of the cured resin core is 2% to 80% of the magnetic path length of the entire composite magnetic core. 3. A magnetic core made of a bulk soft magnetic material combined with a powdered resin cured magnetic core has a hollow box shape,
3. The composite magnetic core according to claim 1, wherein after the air-core coil is stored in the box in advance, a resin slurry in which powders A and B are mixed is poured into the box and hardened.