JP3097484B2 - choke coil - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a choke coil mainly used for removing noise flowing out of an electronic device or the like.

[0002]

BACKGROUND OF THE INVENTION Generally, a common mode choke coil has a small amount of a normal mode leakage inductance component, and thus is effective for normal mode noise. Separately, it was necessary to take countermeasures against noise using a normal mode choke coil.

[0003] In the case of a common mode choke coil having a relatively large leakage inductance component in a normal mode, the leakage magnetic flux may have an adverse effect on peripheral circuits. For this reason, it is necessary to take measures such as applying a magnetic shield to the outer periphery of the common mode choke coil. As a countermeasure, for example, as shown in FIG. 8, the applicant has disclosed a bobbin 51 made of a magnetic material, a magnetic core 60 inserted through the bobbin 51, and a pair of windings 54 wound around the bobbin 51. , 55 are proposed.

[0004]

This choke coil can remove both the common mode noise and the normal mode noise. However, if the magnetic material core 60 is simply inserted through the bobbin 51, the choke coil can be connected to the bobbin 51. Since the gap between the magnetic cores 60 cannot be sufficiently secured, the bobbin 51
And the magnetic resistance between the magnetic core 60 and the magnetic core 60 becomes low, and the magnetic flux φ5 generated in the bobbin 51 due to the normal mode noise easily leaks to the magnetic core 60 having a high relative magnetic permeability. As a result, this choke coil has a problem that saturation of the common mode noise easily occurs, and it is not possible to sufficiently exert the noise removing effect on the common mode noise.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a choke coil that hardly causes saturation of common mode noise and has a sufficient noise removing effect on common mode noise and normal mode noise.

[0006]

In order to achieve the above object, a choke coil according to the present invention comprises: (a) a pair of windings; and (b) a cylindrical body around which the pair of windings is wound. A bobbin made of a magnetic material and having a closed magnetic path surrounding each of the pair of windings; and (c) a magnetic core inserted through a cylindrical body of the bobbin; Providing a gap forming projection on at least one of the hole wall surface of the cylindrical body of the bobbin or the surface of the magnetic core,
It is characterized by.

[0007]

With the above arrangement, the gap forming projections
A gap of a predetermined size is secured between the hole wall surface of the cylindrical body of the bobbin and the surface of the magnetic core. Therefore, the magnetic resistance between the bobbin and the magnetic core increases, and the magnetic flux generated in the bobbin due to the normal mode noise hardly leaks to the magnetic core.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a choke coil according to the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 1, the choke coil includes a bobbin 1, a pair of windings 4 and 5 wound around the bobbin 1, respectively, and two U-shaped magnetic cores 10 and 11. . Bobbin 1
Is a cylindrical body 1a, flanges 1b, 1c, 1d provided at both ends and a center of the body 1a, and flanges 1b to 1d.
And a lid 1f joined to the outer peripheral end surface of the cover.
In the case of the present embodiment, the lid 1f does not cover the entire outer peripheral end surfaces of the flanges 1b to 1d, but it goes without saying that it may cover the entire outer periphery. The material of the bobbin 1 has a relative magnetic permeability of 1
The above (for example, two to several tens) insulating magnetic material is used. Specifically, a material obtained by kneading a Ni-Zn or Mn-Zn ferrite and a resin binder is used.

On the wall surface of the opening of the hole 1e of the cylindrical body 1a, a projection 8 for forming a gap is provided.
Is sufficiently secured by the gap forming projections 8. The height of the gap forming projections 8 is determined by the magnetic resistance between the bobbin 1 and the cores 10 and 11, which corresponds to the points A and B shown in FIG.
It is set to be larger than the magnetic resistance between points. For example, if the relative magnetic permeability of the bobbin 1 is 20 and the distance between the points A and B is 10 mm, the height of the projection 8 is about 0.5 mm. As the material of the gap forming projections 8, the same material as that of the bobbin 1 may be used, or a different material may be used.

A pair of windings 4 and 5 are wound around a body 1a of the bobbin 1 with a flange 1c interposed therebetween, and start and end portions thereof are terminals (not shown) provided on the bobbin 1. )). The bobbin 1 forms a closed magnetic circuit that circumvents the winding 4 with the upper half of the body 1a, the flange 1b, the upper half of the lid 1f, and the flange 1c, and the lower half of the body 1a, the flange 1d, The lower half of the portion 1f and the flange portion 1c constitute a closed magnetic circuit that goes around the winding 5.

The magnetic cores 10 and 11 are joined while being inserted into the hole 1e of the body 1a of the bobbin 1 to form a square-shaped core. As a material of the cores 10 and 11,
It is preferable that the relative permeability is several thousand, and specifically, ferrite, amorphous, or the like is used. The choke coil having the above-described structure is provided with the bobbin 1 by the gap forming projections 8.
Since the gap between the magnetic cores 10 and 11 is sufficiently ensured, the magnetic resistance between the bobbin 1 and the magnetic cores 10 and 11 is large, and the magnetic flux generated in the bobbin 1 by the normal mode noise is generated by the magnetic core. It is hard to leak to 10 and 11. As a result, it is possible to obtain a choke coil in which saturation of the common mode noise hardly occurs and which can sufficiently exhibit the noise removing effect on the common mode noise and the normal mode noise. FIG. 2 is an electric equivalent circuit diagram of the choke coil.

FIGS. 3 and 4 show the common mode noise removing operation of the choke coil having the above configuration.
This will be described with reference to FIG. As shown in FIG. 3, the choke coil is electrically connected to two signal lines provided between a power supply 20 and a load 21 such as an electronic device. A stray capacitance C1 is generated between the power supply 20 and the ground, and a stray capacitance C2 is generated between the load 21 and the ground. When the common mode noise currents i ₁ and i ₂ flow in the two signal lines in the directions of the arrows in the figure, as shown in FIG.
φ2 occurs. The magnetic fluxes φ1 and φ2 are added to each other and orbit in the closed magnetic path of the cores 10 and 11, and gradually attenuate without leaking to other parts. This is because the magnetic fluxes φ1 and φ2 are converted into thermal energy in the form of eddy current loss or the like. Thereby, the common mode noise currents i ₁ and i ₂ are reduced.

Next, the normal mode noise removing operation of the choke coil will be described with reference to FIGS. As shown in FIG. 5, the normal mode noise current i ₃
Flows through the two signal lines in the directions of the arrows in the figure, as shown in FIG. 6, magnetic fluxes φ3 and φ4 are generated in the windings 4 and 5, respectively. Since the gaps between the cores 10 and 11 and the bobbin 1 are sufficiently secured by the gap forming projections 8, the magnetic flux φ
While rotating around the closed magnetic path of the bobbin 1 without leaking to the cores 10 and 11, the φ3 and φ4 are converted to thermal energy in the form of eddy current loss and gradually attenuated. Thereby, the normal mode noise current i ₃ is reduced.

The choke coil according to the present invention is not limited to the above embodiment, but can be modified within the scope of the invention. The gap forming projections may have any shape. For example, as shown in FIG. 7, strip-shaped triangular projections 31 are arranged at equal intervals on the inner wall surface of the hole 1e of the cylindrical body in the axial direction of the body. Is also good. The gap-forming projections may be provided not on the cylindrical body but on the magnetic core or on both.

The bobbin does not need to be one common bobbin for a plurality of windings, but may be a plurality of independent bobbins corresponding to each of the windings. May have a cylindrical shape or a rectangular tube shape. Further, the core may be a combination of two U-shaped cores or E-shaped cores, or a combination of a U-shaped core or E-shaped core with an I-shaped core. Alternatively, the core is not limited to a split type, but may be an integral type, for example, a Japanese character core or a square character core.

[0016]

As apparent from the above description, according to the present invention, the gap forming projection is provided on at least one of the hole wall surface of the cylindrical body of the bobbin and the surface of the magnetic core. The gap between the bobbin and the magnetic core can be sufficiently ensured, and the magnetic flux generated in the bobbin due to the normal mode noise hardly leaks to the magnetic core. As a result, it is possible to obtain a choke coil that hardly saturates the magnetic flux due to the common mode noise and has a sufficient noise removing effect on the common mode noise and the normal mode noise.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a choke coil according to the present invention.

FIG. 2 is an electric equivalent circuit diagram of the choke coil shown in FIG.

1. FIG. 3 is an electric circuit diagram for explaining common mode noise removal by the choke coil shown in FIG.

FIG. 4 is a magnetic circuit diagram for explaining common mode noise removal by the choke coil shown in FIG. 1;

FIG. 5 is an electric circuit diagram for explaining normal mode noise removal by the choke coil shown in FIG. 1;

FIG. 6 is a magnetic circuit diagram for explaining normal mode noise removal by the choke coil shown in FIG. 1;

FIG. 7 is a perspective view of an inner peripheral surface of a bobbin showing another embodiment.

FIG. 8 is a sectional view showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Bobbin 1a ... Cylindrical trunk | drum 1b, 1c, 1d ... Flange 1e ... Hole 1f ... Lid 4,5 ... Winding 8 ... Gap formation projection 10, 11 ... Magnetic core 31 ... Gap formation triangular projection

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Iwao Fukuya 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Murata Manufacturing Co., Ltd. (56) References JP-A-5-299273 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01F 17 / 04,27 / 00,37 / 00

Claims (1)

(57) [Claims] 1. A pair of windings, a cylindrical body around which the pair of windings are wound, and the cylindrical body
End flanges respectively provided at both ends of the cylindrical body,
A central flange provided at the center of the pair and separating the pair of windings
A bobbin made of a magnetic material having a closed magnetic circuit that goes around each of the pair of windings, and a magnetic core inserted into a cylindrical body of the bobbin. Providing a gap forming protrusion on at least one of the hole wall surface of the trunk or the surface of the magnetic core ,
The magnetic resistance between the bobbin and the magnetic core is
Larger than the magnetic resistance between the end flange and the center flange of the cylindrical body
Wherein the height of the gap-forming projections is set so as to be smaller .