JP2002353038A - Ferrite core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust the air gap easily while reducing the labor required for polishing and enhancing the accuracy of polishing, and to enhance productivity by preventing chipping or damage. SOLUTION: In the ferrite core where a magnetic path is formed by bonding a plurality of cores, at least one core has such a structure as a plurality of thin core members of substantially identical shape having a plurality of leg parts are pasted and a step is formed at the forward end of leg parts pasted while differentiating the length of at least a part of leg parts of a part of the thin core member from the length of leg part of other thin core members. For example, an E-type core 28 has such a structure as first and second E-type thin core members 20 and 22 are pasted and the length at the intermediate leg part of the second E-type thin core member is set shorter than that of the first E-type thin core member thus forming a step at the forward end of the pasted intermediate legs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferrite core used in a choke coil, a transformer, and the like. The present invention relates to a ferrite core in which a desired step is formed at the tip of a bonded foot so as to be different from the length of the other foot. Although this ferrite core is not particularly limited, it is useful, for example, for a nonlinear choke coil used in a switching power supply.

[0002]

2. Description of the Related Art Recently, a choke coil incorporated in a secondary DC load circuit of a switching power supply has a large inductance for a small DC load current and a small inductance for a large DC load current. A choke coil whose inductance changes non-linearly with respect to a direct current is used. By using such a non-linear choke coil, the controllability of the output voltage at the time of no load can be improved, and wasteful power consumption due to the dummy current can be suppressed.

In such a non-linear choke coil, a ferrite core having a gap in a part of a magnetic path cross section is used. The ferrite core is EE type core or E-
An I-type core, for example, as shown in FIG.
Steps are applied to the tip of the midfoot 0 to form a portion having a gap and a portion having no gap in the magnetic path cross section. When the DC current flowing through the coil is small, a portion having no air gap becomes a magnetic path and a high inductance is generated. If the DC current flowing through the coil is large, portions without gaps will be magnetically saturated, but portions with gaps will not be magnetically saturated, resulting in low inductance. In this way, a non-linear characteristic of the inductance is obtained.

The stepped shape of the tip of the middle foot of the E-shaped core includes a shape shown in FIG. 5 in which one side is cut out, and a shape in which both sides are cut out so as to be convex.

[0005]

In any case, the stepped shape of the tip of the middle foot of the E-shaped core is formed by polishing.
In order to exhibit desired non-linear characteristics, it is necessary to strictly control the width a of the portion left without polishing and the depth b of the portion to be polished. The width a is determined, for example, with reference to the core side surface (the left side surface in FIG. 5).

However, since the ferrite core is obtained by firing a molded body, the dimensional accuracy of the fired product is naturally limited, and the foot may be slightly bent. Therefore, adjustment work such as changing the width and position of polishing is required one by one. Further, the polishing direction is parallel to the tip surface of the middle foot (indicated by an arrow in FIG. 5), but the tip of the middle foot is partially cut so that a cut surface is generated in a direction perpendicular to the tip surface of the middle foot. If the polishing rate is too high, the chipping or breakage is liable to occur, and it is very difficult to set the polishing operation conditions. For this reason, there has been a problem that polishing workability is extremely poor.

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the number of polishing steps and improve the polishing accuracy, to easily adjust the gap, to prevent chipping or breakage at the time, and to increase the productivity. It is to provide a ferrite core devised.

[0008]

According to the present invention, there is provided a ferrite core having a magnetic path formed by joining a plurality of cores, wherein at least one of the cores has a plurality of substantially identical thin cores having a plurality of feet. In a bonding structure of members, a step is formed at a tip end of the bonded foot so that at least a part of a foot of a part of the thin core is different from a corresponding foot of another thin core member. A ferrite magnetic core characterized in that the ferrite core is made to have the above configuration.

Further, the present invention provides a ferrite core comprising two E-shaped cores combined so that the tip surfaces of their feet are joined to each other, wherein at least one of the E-shaped cores comprises a plurality of E-shaped thin core members. A ferrite core, wherein the ferrite core has a laminated structure, wherein the length of at least one foot is different from the length of the other foot so that a step is formed at the tip of the laminated foot. It is. For example, one E-type core has a unitary structure, and the other E-type core has a first structure.
And an E-shaped thin core member and a second E-shaped thin core member. Then, the length of the middle foot portion of the second E-shaped thin core member is made shorter than the length of the middle foot portion of the first E-shaped thin core member, and a predetermined step is formed at the tip of the bonded middle foot. To be done.

[0010] Further, the present invention provides an E-type core and an I-type core,
In the ferrite magnetic core in which the tip surfaces of the foot portions of the mold core are combined so as to be joined to the I-type core, the E-type core has a structure in which a plurality of E-type thin core members are bonded to each other. A ferrite core characterized in that the length is different from the lengths of the other foot portions so that a step is formed at the tip of the bonded foot portions. For example, the E-shaped core has a structure in which a first E-shaped thin core member and a second E-shaped thin core member are bonded to each other, and the length of the middle foot portion of the second E-shaped thin core member is set to the first length. The length of the middle foot portion of the E-shaped thin core member is shorter than that of the middle foot portion so that a predetermined step is formed at the tip of the bonded middle foot.

[0011] These ferrite cores are particularly useful as cores for nonlinear choke coils.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is typically applied to an EE type or EI type ferrite core. Is also applicable. The number of thin core members to be bonded may be usually two, but it is also possible to bond three or more thin core members. Even when two pieces are bonded, the thickness of both thin core members may be the same or different. Only one portion of the thin core member may be shortened, but a plurality of portions may be used. In the case of an EE type core or a UU type core, only one of the cores may have a bonded structure, but both of the cores may have a bonded structure.

In the case of a thin core member having a short foot portion, the length of the gap is adjusted by polishing the entire front end of the foot portion. However, if the size to be polished is large, it should be formed in advance in consideration of the length. Is also possible. After laminating the thin core member, all the foot end surfaces can be lightly polished to make all the foot lengths uniform and smooth the front end surfaces.

The ferrite core having such a structure can be used not only for a choke coil for electronic equipment but also for a transformer.

[0015]

FIG. 1 is an explanatory view showing one embodiment of a ferrite core for a nonlinear choke coil according to the present invention, and shows an E-shaped core having a laminated structure. In this example,
Two substantially identical E-shaped thin core members are attached to each other. The first E-shaped thin core member 20 has a thin structure in which the middle foot is the same length as the outer foot on both sides, but is about half the originally required thickness. The second E-shaped thin core member 22 has a thin structure in which the middle foot is shorter than the outer feet on both sides by the length c, and is about half (thickness d) of the originally required thickness. The second E-shaped thin core member 22 is polished in the polishing direction indicated by the arrow to adjust the middle foot length. In this case, since the middle foot is entirely polished, chipping or breakage hardly occurs even if the polishing speed is increased.

The first and second E-shaped thin core members 20 and 22 having a predetermined shape are bonded and integrated using an adhesive 24. As a result, an E-shaped core 28 having a desired step 26 formed at the tip of the middle foot is obtained. If the core temperature during use becomes high, use a heat-resistant adhesive that can cope with this. The reason why the first and second thin core members 20 and 22 are bonded and integrated is that if the core members are not bonded and the core members are displaced, the electrical characteristics change.

As shown in FIG. 2, the E-shaped core 28 having such a bonding structure has a coil 30 wound around a middle foot.
A choke coil is formed by combining with a normal integrated E-shaped core 32. FIG. 3 shows the DC superimposition characteristics of the manufactured choke coil. Non-linear characteristics exhibiting high inductance when the DC current is small and low inductance when the DC current is large are obtained.

The E-shaped core 28 having such a bonding structure
As shown in FIG. 4, the coil 30 is wound around the middle foot,
A non-linear choke coil can be manufactured by combining with a normal integral type I core 34.

[0019]

As described above, the present invention is a ferrite magnetic core in which a step structure is formed at the tip of a foot by bonding the thin core member whose height of the foot has been adjusted in advance to another thin core member. In addition, the number of polishing steps can be reduced and the polishing accuracy can be improved, and the gap can be easily adjusted. Polishing process,
Since the polishing is performed on the entire surface of the foot portion of the thin core member, chipping or breakage hardly occurs even if the polishing rate is increased, the productivity can be increased, and the yield can be improved. Further, variation in characteristics due to polishing accuracy can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of an E-shaped core having a bonding structure used in the present invention.

FIG. 2 is an explanatory diagram of a nonlinear choke coil using the same.

FIG. 3 is a graph showing an example of the DC superimposition characteristic.

FIG. 4 is an explanatory diagram showing another configuration example of the nonlinear choke coil.

FIG. 5 is an explanatory view showing an example of an E-shaped core used in the related art.

[Explanation of symbols]

 Reference Signs List 20 first E-shaped thin core member 22 second E-shaped thin core member 24 adhesive 26 step 28 E-shaped core of bonded structure

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Satoshi Ota 5-36-11 Shimbashi, Minato-ku, Tokyo FDC Corporation (72) Inventor Yuji Inda 5-36 Shimbashi, Minato-ku, Tokyo No. 11 FDC Corporation (72) Inventor Masami Nonaka 5-36 Shimbashi, Minato-ku, Tokyo FDC Corporation

Claims (6)

[Claims] 1. A ferrite magnetic core in which a magnetic path is formed by joining a plurality of cores, wherein at least one of the cores has a structure in which a plurality of substantially identical thin core members having a plurality of feet are bonded. The length of at least some of the thin core members may be different from the corresponding length of the other thin core members, and a step may be formed at the tip of the bonded foot. Ferrite core. 2. A ferrite core in which two E-shaped cores are combined so that tip surfaces of respective feet are joined to each other, wherein at least one of the E-shaped cores is formed by bonding a plurality of E-shaped thin core members. A ferrite core characterized in that at least one foot portion has a length different from that of another foot portion so that a step is formed at the tip of the bonded foot portion. 3. One E-shaped core has an integral structure, and the other E-shaped core has a structure in which a first E-shaped thin core member and a second E-shaped thin core member are bonded to each other. The length of the middle foot of the E-shaped thin core member is shorter than the length of the middle foot of the first E-shaped thin core member, so that a step is formed at the tip of the bonded middle foot. Item 2. A ferrite core according to Item 2. 4. A ferrite core obtained by combining an E-shaped core and an I-shaped core such that a tip end surface of a foot portion of the E-shaped core is joined to the I-shaped core, wherein the E-shaped core comprises a plurality of E-shaped thin cores. A structure in which members are attached to each other, wherein the length of at least one foot is different from the length of the other feet, so that a step is formed at the tip of the attached feet. Ferrite core. 5. The E-shaped core has a structure in which a first E-shaped thin core member and a second E-shaped thin core member are bonded to each other, and a length of a middle foot portion of the second E-shaped thin core member. 5. The ferrite core according to claim 4, wherein the length of the middle foot portion of the first E-shaped thin core member is shorter than that of the first E-shaped thin core member so that a step is formed at the tip of the bonded middle foot. 6. The ferrite core according to claim 1, wherein the ferrite core is a core for a nonlinear choke coil.