JP2001244120A - Dust core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dust core which is superior in a frequency characteristic and a DC superposition characteristic, for which a circuit can be designed easily and which can be manufactured easily and inexpensively. SOLUTION: The dust core is constituted by a molded body 1, in which magnetic powder and resin are molded and heat-treated and a gap part is provided, and a silicone rubber sheet 2 to be inserted into the gap part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dust core for a reactor mounted on a power supply having a switching frequency of 10 kHz or more, among switching power supplies mounted on industrial equipment and general household electric appliances. Regarding the structure.

[0002]

_2. Description of the Related Art In recent years, energy-saving and CO2 problems have been increasing, and energy-saving measures have been rapidly progressing in general home electric appliances and industrial equipment. In general, those that use a motor such as an air conditioner or a refrigerator, lighting equipment, and the like can be cited as those having high power consumption and high energy saving measures. In order to promote energy saving of these products, adoption of high-efficiency motors, higher efficiency of electric circuits, and the like are being promoted. A major problem in the efficiency of electric circuits is a power supply unit that converts 50/60 Hz AC input into DC. In order to improve the efficiency, switching power supplies have been rapidly spreading in recent years.

[0003] However, when a switching power supply is employed, the generation of a harmonic current becomes a problem due to the distortion of the current waveform. As a countermeasure, various circuit methods have been proposed, for example, a choke input method, a one-stone converter method, an active filter method, and the like.In each case, a reactor is used to increase the conduction angle of current. Is done. In addition to the inductance value, the characteristics required for this reactor are diverse, such as high conversion efficiency, no swell in the audible range, small temperature rise, small size and light weight, and low cost.

There are various methods for achieving these characteristics, but the most effective means that can be simultaneously solved is as follows.
It is conceivable to increase the switching frequency. In that case, the reactor material to be used is important, and a material having low loss up to high frequencies, high rated permeability and high magnetic permeability is required. In fact, it is a well-known fact that commercialization of a high-frequency ferrite material greatly contributes to the design of a high-frequency power supply for a small-capacity power supply.

On the other hand, in a large capacity power supply, in addition to the above characteristics,
DC superposition characteristics are important, and ferrite materials with low saturation magnetization cannot be used. Therefore, other reactor materials must be used. However, general silicon steel sheets cannot be used due to large core loss at high frequencies, and even high silicon steel sheets cannot be used.
When the frequency exceeds kHz, the magnetic core loss sharply increases and the magnetic permeability significantly deteriorates, so that the operating frequency is limited to 20 kHz or less.

Next, since amorphous B requires the use of expensive B and a special manufacturing apparatus, the cost is inevitably high, and since the magnetostriction is large, undulation in the audible range cannot be avoided. Not the optimal material.

On the other hand, the dust core has good frequency characteristics, but is inferior in DC superposition characteristics as compared with high silicon steel sheets. A method of improving the superposition characteristics by providing a gap in the magnetic path has also been used, but as the superposition current increases,
The problem that the inductance value is reduced still exists. Therefore, the only way to obtain a desired inductance value with a predetermined superimposed current is to use a large magnetic core, and even in this case, if the superimposed current value changes, the inductance value also greatly changes. However, it is difficult in terms of external circuit design and reduction in size and weight.

[0008]

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a dust core which has excellent frequency characteristics and direct current superposition characteristics, is easy to design a circuit, and can be easily and inexpensively manufactured. To provide.

[0009]

Means for providing a gap in a magnetic path include a method of cutting a part of a joint, which is often used for an E-shaped magnetic core, and a method of cutting a thick paper or FRP on the joint.
There is a spacer gap method in which a nonmagnetic material is interposed, and the present invention is applied to the latter method. As the spacer to be inserted at this time, a spacer which is not easily deformed is inserted for the purpose of keeping the gap amount constant and keeping the inductance value at a predetermined value. In the present invention, the spacer portion is formed of a material that does not reach the elastic limit even if the elastic body is deformed by 20% or more.

That is, the present invention is a dust core comprising a molded body having a gap formed by molding and heat-treating a magnetic powder and a resin, and an elastic body inserted into the gap.

The present invention also provides the dust core as described above, wherein the elastic body is made of a substance that does not reach the elastic limit even if it is deformed by 20% or more.

According to this method, a special device for manufacturing the reactor is not required, so that the reactor can be easily and inexpensively provided.

When a DC superimposed current is flowing, a magnetic field is generated inside the magnetic core by the current. The magnetic flux φ at this time can be expressed as follows using the inductance value L and the superimposed current value I.

Φ = LI

In the gap, the magnetic flux exits from one magnetic core and enters the other magnetic core. As a result, NS at the tip of the gap portion
Magnetic poles are created and an attractive force is created. The attractive force F per unit cross-sectional area of the gap can be represented by the following equation using the magnetic flux density B and the magnetic field H at the gap.

F = (B · H) / 2

Here, assuming that the thickness of the spacer inserted in the gap portion is D and the longitudinal elastic modulus is E, the thickness of the spacer is changed by the suction force F by an amount represented by the following equation.

ΔD = D · F / E

The inductance value per turn of the magnetic core, that is, the AL value, changes according to the gap amount, that is, the total sum G of the spacer thicknesses, as follows.

AL = (AL ₀ ) · G ^α

Here, AL ₀ is the AL value when there is no gap. In most of the spacer gap methods, spacers are arranged at two positions.
= 2D.

For this reason, when the superimposed current increases, the gap contracts due to the attraction force, and attempts to increase the AL value. As a result, a decrease in the inductance component due to an increase in the superimposed current is mitigated, and a magnetic core having a DC superimposition characteristic that is flatter than the conventional superimposed current value can be obtained.

[0023]

Embodiments of the present invention will be described below.

(Embodiment 1) 6. Fabricated by pulverization method
5 wt% Si-1.0 wt% Mn-balFe alloy powder was classified to 150 μm or less, and 2 wt% of a Si-based resin as a binder was mixed at a weight ratio. Next, using a molding die, the die was formed into an outer diameter of 27 mm, an inner diameter of 14 mm, and a height of 8 mm. Next, the molded body was kept at 700 ° C. × 2 hours in an inert atmosphere, and then gradually cooled to room temperature.

Further, as shown in FIG.
Is cut into two U-shapes, and the cut surface is polished.
They were assembled via a silicone rubber sheet 2 of 0.2 mm thickness and 5 mm square. At this time, the silicone rubber sheet 2
0.2mm thick and 1mm wide to prevent excessive force from being applied
The solid silicone varnish 3 formed in the above was disposed on both sides thereof.

In this state, a glass fiber tape was wound to provide electrical insulation, and then immersed in methanol to dissolve and remove the silicone varnish 3. After drying, a primary winding of 120 turns and a secondary winding of 30 turns were wound on the glass fiber tape, and the winding was performed using a Hewlett-Packard HP4284A, LCR meter and 42841A DC superimposed current source.
100 kHz when 0AT DC current is superimposed,
The inductance value at 0.2 mA was measured.

As a comparative example, a magnetic core was produced by combining magnetic cores of exactly the same shape with a thick paper having a thickness of 0.2 mm interposed therebetween.
The same tape winding and winding were performed, and the superposition characteristics were measured. The result is shown in FIG.

As shown in FIG. 2, it can be seen that the magnetic core manufactured in the present embodiment has better DC superposition characteristics than the comparative example. Further, for the silicone rubber sheet used in the present embodiment, the strain amount when the elastic limit was reached with respect to the compressive stress was measured using a tensile tester.
%Met.

(Embodiment 2) As shown in FIG. 3, a molded article 1 manufactured in the same manner as that used in Embodiment 1 is coated with a paint for insulation and dried. 2
After being cut into two U-shapes, the cut surface was polished, and stored in a cylindrical plastic case 4 having an opening in the center of the plane. At this time, silicone grease was applied to the inner wall of the plastic case 4 for the purpose of lubrication and release. Then, two naphthalenes 5 each having a thickness of 0.2 mm, a width of 1 mm, and a length of 10 mm are inserted into opposite portions of the cut surface to form gaps, and a commercially available cold-curable silicone rubber 6 is inserted into the gaps. Was poured. After 6 hours, they are immersed in ethanol and
Was dissolved and removed.

After drying, the first 120 turns, the second 3
0 turn winding, Hewlett-Packard H
As a result of measuring the inductance value at 100 kHz and 0.2 mA when the DC current was superimposed up to 1200 AT using the P4284A, LCR meter and 42842A DC superimposed current source, the same result as in the first embodiment was obtained. .

For the silicone rubber 6 used in the present embodiment, the amount of strain when reaching the elastic limit with respect to compressive stress was measured using a tensile tester.
%Met.

In the above embodiment, silicone rubber is used. However, other synthetic rubbers can be used in consideration of heat resistance and elastic limit to compressive stress. For example, fluorine rubber, styrene-butadiene rubber, ethylene-propylene rubber, and the like.

[0033]

As described above, according to the present invention,
Provided is a dust core which has excellent frequency characteristics and direct current superposition characteristics, is easy to design a circuit, and can be easily and inexpensively manufactured.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a method for manufacturing a dust core according to Embodiment 1 of the present invention. FIG. 1A is a plan view. FIG. 1 (b)
Is a side view.

FIG. 2 is a characteristic diagram showing a comparison between the dust cores of the first embodiment and a comparative example.

FIG. 3 is an explanatory view illustrating a method for manufacturing a dust core according to Embodiment 2 of the present invention. FIG. 3A is a plan view. FIG. 3 (b)
Is a sectional view.

[Description of Signs] 1 molded body 2 silicone rubber sheet 3 silicone varnish 4 plastic case 5 naphthalene 6 silicone rubber A present invention B comparative example

Claims (2)

[Claims] 1. A dust core comprising a molded body having a gap formed by molding a magnetic powder and a resin and performing heat treatment, and an elastic body inserted into the gap. 2. The dust core according to claim 1, wherein the elastic body is made of a material that does not reach an elastic limit even when deformed by 20% or more.