TWI390559B - Transformer - Google Patents

Description

transformer

The present invention relates to a small-sized transformer for use in various electronic/electrical devices and the like, and more particularly to a discharge of a cold cathode discharge lamp (CCFL) for backlights that is mounted on various display panels such as a notebook computer and a liquid crystal television. An inverter transformer used in a lighted DC/AC inverter circuit.

In general, in the transformer, in order to ensure the insulation turbulence between the primary winding and the secondary winding, it is required to ensure a creepage distance above a certain distance between the primary winding and the secondary winding (creepage distance). ).

This kind of creeping distance is not a problem in a large-scale transformer. However, for transformers such as electronic equipment and notebook computers that are used for miniaturization every year, the requirements for miniaturization of the transformer main body are also severe. Both the securing and miniaturization of the creeping distance have become important issues.

In the conventionally proposed variator proposed to solve the above problems, the following Patent Document 1 is known. The transformer described in Patent Document 1 has a first bobbin having a first winding portion wound once, and a second bobbin having a second winding portion wound twice. The tube is disposed coaxially, and a cylindrical housing portion is provided on the other end side in the axial direction of the first winding portion, and the second winding portion in which the winding is wound twice is inserted in the housing portion. .

Patent Document 1: Japanese Laid-Open Patent Publication No. 2007-173359

In the transformer described in Patent Document 1, the second winding portion that is wound twice is inserted into the housing portion provided in the first bobbin, and the winding is performed once and twice. In the coaxial arrangement, the creeping distance of the length of the side surface of the accommodating portion can be additionally ensured, and the primary winding and the secondary winding can be arranged close to each other in the axial direction. Therefore, the length in the axial direction can be obtained. However, since the winding is covered by the accommodating portion for the secondary winding, the following problems occur.

In other words, in recent years, the voltage supplied to the general household (AC100V in Japan) is directly input to the primary winding. When the transformer is used to step down the supply voltage, a large current is generated in the secondary winding. Therefore, it is difficult to release the heat generated in the secondary winding to the outside by the above-described configuration in which the secondary winding is covered by the accommodating portion.

On the other hand, when heat dissipation is considered, it is preferable to adopt a configuration in which not only the secondary winding but also the primary winding is not covered, but the primary winding and the secondary winding are coaxial. In the case of the arrangement of the mode, in order to secure a certain creeping distance, it is necessary to arrange the primary winding and the secondary winding away from each other in the axial direction, thereby causing a problem that the length of the entire axial direction of the transformer increases. Further, in general, when the distance between the primary winding and the secondary winding becomes long, the coupling between the two becomes poor, and the conversion efficiency of the transformer is lowered.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a creeping distance between a primary winding and a secondary winding which are disposed coaxially with each other, and which can shorten the length of the entire axial direction of the transformer. And a transformer with excellent heat dissipation.

In order to achieve the above object, the transformer of the present invention is constructed as follows.

That is, the transformer of the present invention includes: a first winding; a second winding electromagnetically coupled to the first winding; and a first winding portion that winds the first winding and penetrates the first winding a first bobbin of the first through hole inside the portion; a second bobbin having a second winding portion that winds the second winding and a second through hole that penetrates the inside of the second winding portion And a core inserted into the first through hole and the second through hole; and configured to arrange the first bobbin and the second bobbin coaxially;

The first bobbin includes a hollow extending portion extending from one end portion of the first winding portion in the axial direction toward the second bobbin and having the iron core inserted therein;

The second through hole of the second bobbin includes an insertion port into which the extending portion is inserted at one end portion of the second through hole in the axial direction, and the insertion hole is oriented in the axial direction of the second through hole. A certain range of portions extending at one end portion is formed as a large hole portion, and the large hole portion is formed to have a certain air gap along the entire circumference between the outer peripheral surface of the extending portion inserted from the insertion port. size.

In the transformer of the present invention, the second bobbin may be provided with a partition flange for dividing the second winding portion into a plurality of winding regions.

Further, a portion of the second through hole in the axial direction on the other end side of the second bobbin may be formed to be smaller than the large hole portion and to be able to insert the core. a small hole portion, and a portion between the small hole portion and the large hole portion is formed as a middle hole portion having a size that fits between the large hole portion and the small hole portion and is engageable with the extending portion.

In the present invention, the first winding is used as the primary winding, and the second winding is used as the secondary winding. Alternatively, the first winding may be used as the secondary winding, and the first winding may be used. 2 winding as a winding.

Further, the transformer of the present invention includes: a first bobbin that winds the winding on the input side; a second bobbin that winds the winding on the output side; and the first one that is inserted coaxially a through hole of the bobbin and an inner core of the through hole of the second bobbin; wherein

One of the first bobbin and the second bobbin has an extension on a side in contact with the other bobbin;

One end of the through hole of the other bobbin is provided with an insertion port for inserting the extension portion;

The inner circumference of the through hole of the other bobbin and the outer circumference of the extending portion are spaced apart from each other by a certain distance.

In this case, the second bobbin may be provided with a plurality of partitioning flanges for dividing a region around which the winding on the output side is wound.

Further, in the through hole of the other bobbin, the portion on the side of the insertion port may be formed as a large hole portion that can be separated from the outer circumference of the extending portion by a predetermined distance. a portion on the opposite side of the insertion port is smaller than the large hole portion and is formed in a small hole portion that can be inserted into the core, and a portion between the small hole portion and the large hole portion is formed as The large hole portion and the intermediate hole portion of the size of the small hole portion and capable of being fitted to the extending portion.

According to the above configuration, the transformer of the present invention achieves the following effects.

In other words, the hollow extending portion extending from the one end portion of the first winding portion in the axial direction of the first bobbin is inserted from the second bobbin at the one end portion of the second through hole in the axial direction. Inserted in the large hole portion, and a certain air gap is ensured along the entire circumference between the outer peripheral surface of the inserted extending portion and the large hole portion, whereby the first winding is simpler than the first surface When the tube and the second bobbin are disposed coaxially, at least a large hole portion can be secured between the first winding wound around the first winding portion and the second winding wound around the second winding portion. The amount of back and forth distance of the length of the axis direction.

Therefore, since a certain creeping distance is ensured between the first and second windings, and the first winding and the second winding can be arranged close to each other in the axial direction, the length of the entire axial direction of the transformer can be Shortened.

Further, since the one inserted into the large hole portion is an extending portion extending from one end portion of the first winding portion in the axial direction, and the first winding portion is not inserted into the large hole portion, the first one is used as compared with the first hole portion. When the winding is inserted into the large-hole portion, the first winding wound around the first winding portion is excellent in heat dissipation and does not cover the second winding wound around the second winding portion. Since the surrounding wrap is applied, the heat dissipation of the second winding is also excellent.

Hereinafter, embodiments of the transformer of the present invention will be described in detail with reference to the accompanying drawings. Figs. 1 to 4 show a first embodiment of the transformer of the present invention, and Figs. 5 and 6 show a second embodiment of the transformer of the present invention. In the first to fourth figures, in order to clearly distinguish the correspondence between the directions of the drawings, the three-dimensional coordinate system composed of three orthogonal X, Y, and Z axes is similarly In the fifth to sixth figures, in order to make the correspondence between the directions between the two drawings clear, a three-dimensional coordinate system composed of three orthogonal X', Y', and Z' axes is attached.

(First embodiment)

First, a transformer according to a first embodiment of the present invention will be described with reference to Figs. 1 to 4 . Fig. 1 is a front elevational view showing the overall configuration of a transformer according to a first embodiment of the present invention, and Fig. 2 is an exploded perspective view showing the transformer. 3 is a cross-sectional view taken along line A-A of FIG. 1, and FIG. 4 is an exploded view of a cross-sectional view shown in FIG. 3.

The transformer 1 of the present embodiment is used as an inverter transformer in a DC-AC inverter circuit that discharges and illuminates a backlight for a cold cathode discharge lamp (CCFL) of various display panels used in a notebook computer or a liquid crystal television. The user, or a transformer used for the purpose of insulation and voltage transformation, as shown in Fig. 1, has the following components: the first winding 2 (only a part is shown in Fig. 1), a second winding 3 (only a part of which is shown in Fig. 1) electromagnetically coupled to the first winding 2, a bobbin unit 4 made of an insulating material such as plastic, and a ferrite The cores 5A, 5B and the terminals 6A to 6G formed of a magnetic material such as ferrite. In the present embodiment, the first winding 2 is used as a primary winding, and the second winding 3 is used as a secondary winding. Further, the bobbin unit 4 is composed of a first bobbin 10 and a second bobbin 20 which are disposed coaxially with each other.

The first bobbin 10 includes a first winding portion 11 that winds the first winding 2 and a first through hole 12 that penetrates the inside of the first winding portion 11 (see FIGS. 2 and 4). a hollow extension extending direction of the axis C ₁ of the first end portion of the winding portion 11 toward the second bobbin 20 13 (hollow portion is formed by a first line through hole 12) from, and is formed in volume 1 terminal base portion 11 about an axis C of the other end portion of the _direction 14, and based on the terminal block 14 is held by the primary-side terminals 6A to 6C. Further, both end portions in the axis line C _direction of the first winding portion 11 are respectively formed with end flanges 15A, 15B, and these end lugs 15A, 15B between the primary winding 2 is wound (refer to FIG.1 Figure).

On the other hand, the second bobbin 20 includes a second winding portion 21 that winds the second winding 3 and a second through hole 22 that penetrates the inside of the second winding portion 21 (see FIG. 2 and FIG. FIG. 4), and are formed in the second terminal block 23A in the axis C _direction both end portions of the winding portion 21, 23B, and these terminals 23A and 23B based units are held terminal 6D secondary side with, 6E And 6F, 6G. Further, the second winding portion 21 is formed with end flanges 24A and 24B at both end portions in the direction of the axis C ₂ , and is formed between the end flanges 21A and 21B to form the second winding portion. 21 is divided into a plurality of (in this embodiment three) spacer region S winding flange 25A, 25B ₁ to S _3, and S in each winding _{area. 1} to S ₃ is wound secondary winding 3 (see Figure 1). Wherein, the partition flanges 25A and 25B are respectively formed with the notch portions 26A, 26B and 26C, 26D for traversing the secondary winding 3 to the adjacent winding region, and the end flange 24B is formed to be useful. It is visually confirmed whether or not the height of the second winding 3 wound around the winding region S ₃ exceeds the height of the bottom surface of the winding region S ₂ .

As shown in FIG. 2, lines of the core 5A is formed in a U shape with two legs 51A, 52A, and 51A and two legs, the other end of the line from the leg portion 51A in the axial direction of one of C ₁ among 52A The portion side (the side on which the terminal block 14 is formed) is inserted into the first through hole 12 of the first bobbin 10 . On the other hand, the core 5B is formed in the same shape as the core 5A, and one leg portion 51B of the two leg portions 51B and 52B is on the other end side from the axis C ₂ direction (the above terminal block is formed). The side of 23B is inserted into the second through hole 22 of the second bobbin 20 described above. Further, the leg portions 52A of the core 5A and the leg portions 52B of the core 5B are in contact with each other at the front end portion of the bobbin unit 4.

Hereinafter, the characteristic configuration of the present embodiment and its action will be described.

The second through hole 22 of the second bobbin 20 is one end portion (end portion on the first bobbin 10 side) in the direction of the axis of the second through hole 22 (the axis C _{2 of} the second winding portion 21). An insertion port 27 into which the extension portion 13 of the first bobbin 10 is inserted is provided, and the other end portion of the insertion port 27 in the direction of the axis C ₂ is sequentially provided with a large hole portion 28L, a middle hole portion 28M, and a small portion. The hole portion 28S (and any of the cross-sectional shapes perpendicular to the axis C _{2 is} rectangular) (see Fig. 4).

The large-hole portion 28L is formed in a portion extending from the insertion port 27 toward the other end portion in the direction of the axis C ₂ (in the present embodiment, the range of the length d ₁ shown in FIG. 3), and is formed as It is possible to ensure a constant air gap along the entire circumference between the outer peripheral surface of the extending portion 13 of the first bobbin 10 inserted from the insertion port 27 (in the present embodiment, the length d ₂ shown in FIG. 3 ₎ The size of the space interval).

Meanwhile, the small hole portion 28S is formed in the portion of the axis line C of the other end side of the _second direction, smaller than the size of the large hole portion 28L, and can be formed to have the leg portion 51B of the core 5B of the inserted size. Further, the intermediate hole portion 28M is formed in a portion between the large hole portion 28L and the small hole portion 28S, and has a size between the large hole portion 28L and the small hole portion 28S, and is formed to be capable of being embedded with the extension portion. The size of the combination.

By forming the second through hole 22 as described above, the distal end portion of the extending portion 13 is fitted into the intermediate hole portion 28M, whereby the first bobbin 10 is held by the second bobbin 20 ( Refer to Figure 3). In this holding state, an air gap having a length d ₂ is ensured along the entire circumference as described above between the outer peripheral surface of the extending portion 13 and the large hole portion 28L. Therefore, in the creeping distance, the winding portion can be wound around the winding portion 27 at a position where the extending portion 13 and the second bobbin 20 are in contact with each other at the position of the insertion hole 27 of the second through hole 22. The distance between the first winding 2 of the winding portion 11 and the second winding 3 wound around the second winding portion 21 is ensured by at least the distance d ₁ of the length d ₁ of the large hole portion 28L in the direction of the axis C ₂ . + The amount of distance of the air interval of length d ₂ . Therefore, the first winding 2 and the second winding 3 can be arranged close to each other in the directions of the axes C ₁ and C ₂ while ensuring a constant creeping distance between the first and second windings 2 and 3, transformer 1 the entire axis C _1, C ₂ longitudinal direction of shortening it is possible, and can be a whole size of a transformer, and enable the first wire 2 and the second wire 3 has a good coupling.

Further, the insertion into the large hole portion 28L is such that the extension portion 13 of the first winding 2 is not wound, and the first winding portion 11 is designed not to be inserted into the large hole portion 28L. Therefore, compared with the configuration in which the first winding portion 11 is inserted into the large hole portion 28L, the first winding 2 wound around the first winding portion 11 is excellent in heat dissipation property, and since it is not covered Since the coating around the second winding 3 of the second winding portion 21 is wound, the heat dissipation property of the second winding 3 is also excellent.

Furthermore, as shown in FIG. 3, in the second bobbin 20, by the end flange. 24A, 24B and three spaced single coil region of the flange 25A, 25B is formed along the S ₁ to S ₃ of The area of each cross section of the above-described axis C ₂ (indicated by x in the drawing) is formed to be equal to each other. That is, the system is configured to width (the direction of the longitudinal axis C ₂₎ each of the winding regions S ₁ to S ₃ lines by winding area S _1, S _2, S ₃ being the order of sequentially becomes smaller, and conversely, each The depths of the winding regions S ₁ to S ₃ (the lengths in the direction perpendicular to the axis C ₂ ) are sequentially increased in the order of the winding regions S ₁ , S ₂ , and S ₃ .

Accordingly, since the winding area S 2 can each secondary winding wound in an amount of ₃ to S ₃₁ are equal to each other, each of the field winding S ₁ to S ₃ ensure insulating property becomes easy to At the same time, the balance between the length of the second winding portion 21 (the length in the direction of the axis C ₂ ) and the height (the length in the direction perpendicular to the axis C _{2 in} FIG. 3 ) can be achieved (for example, according to the present embodiment, When the width of the winding range S ₁ is small, the length of the second winding portion 21 is reduced and the height is increased, and the second winding portion 21 is miniaturized, and as a result, the entire transformer 1 can be obtained. Miniaturization (including low-profile).

(Second embodiment)

Next, a transformer according to a second embodiment of the present invention will be described with reference to FIGS. 5 and 6. Fig. 5 is a front view showing the overall configuration of a transformer according to a second embodiment, and Fig. 6 is a perspective view showing a core and a holding belt of the transformer. Here, the illustration of the first and second windings is omitted.

The transformer 7 of the present embodiment is used as an inverter transformer or the like in the same manner as the above-described transformer 1. The basic configuration is as shown in Fig. 5, and the transformer 1 shown in Figs. 1 to 4 is used. The two-in-one (2 in 1) type of the bobbin unit 4 is arranged side by side. Therefore, in order to avoid repetition, the parts related to the bobbin 4 are denoted by the same reference numerals as those of the users in FIGS. 1 to 4, and detailed description thereof will be omitted. In the following description, only the cores 8A, 8B and the holding band are used. 9 for explanation.

As shown in Fig. 6, the core 8A is an E-shaped type having two outer leg portions 81A and 82A and one middle leg portion 83A, and one of the outer leg portions 81A and 82A is an outer leg portion 81A. The two bobbin units 4 shown in Fig. 5 are placed in the first bobbin 10 of the bobbin unit 4 on the right side in the drawing, and the other outer leg portion 82A is placed in the figure. In the first bobbin 10 of the bobbin unit 4 on the left side. On the other hand, the core 8B is formed in the same shape as the core 8A, and one of the outer leg portions 81B and 82B is disposed in the two bobbin units 4 shown in FIG. The other outer leg portion 82A is placed in the second bobbin 20 of the bobbin unit 4 on the right side in the figure, and is disposed in the second bobbin 20 of the bobbin unit 4 on the left side in the drawing. Further, the front end portions of the intermediate leg portion 83A of the core 8A and the intermediate leg portion 83B of the core 8B are in contact with each other between the two bobbin units 4.

On the other hand, as shown in Fig. 6, the holding belt 9 is composed of a base portion 91 and four claw portions 92A to 92D formed on the lower surface of the base portion 91, and is formed by two claws. The portions 92A, 92B are held in a manner to hold the first bobbin 10 of the bobbin unit 4 located on the left side in the drawing among the two bobbin units 4 shown in Fig. 5, and by the two claw portions The 92C and 92D are held in a manner to hold the first bobbin 10 of the bobbin unit 4 on the right side in the drawing. By attaching the holding tape 9, the distance between the two bobbin units 4 can be kept constant, and the workability when the transformer 7 is mounted on a substrate or the like (not shown) can be improved.

Although the embodiment of the transformer of the present invention has been described above, the present invention is not limited to the above-described aspects, and various changes can be made.

For example, in the above-described embodiment, the first winding 2 is wound once and the second winding 3 is wound twice, but the first winding 2 may be reversed as 2 The second winding 3 is used as the primary winding.

Further, in the above-described embodiment, each of the cross-sectional shapes of the large hole portion 28L, the intermediate hole portion 28M, and the small hole portion 28S perpendicular to the axis C _{2 is} designed to have a rectangular shape, but the cross-sectional shape is not limited to a rectangular shape. Can be designed in a variety of shapes.

Further, the configuration of the core is not limited to the embodiment described above, and a core of various shapes may be combined and used.

Further, in the above-described embodiment, an aspect used as an inverter transformer or the like is described. However, the present invention is not limited to application to an inverter transformer or the like, and may be applied to various transformers used for other purposes, such as a drop. Voltage transformers, etc.

Further, although the second bobbin 20 in the above embodiment has three hole portions (a large hole portion 28L, a middle hole portion 28M, and a small hole portion 28S) having different sizes, the size may be different from each other. Two different hole portions (large hole portion and middle hole portion or large hole portion and small hole portion). Fig. 7 shows a transformer 1' which is a modification of the first embodiment. Fig. 7 is a cross-sectional exploded view of the transformer 1' (corresponding to Fig. 4), and the same members and parts as those of the first embodiment are labeled the same as those of the first to fourth figures. Numbering.

As shown in Fig. 7, the second bobbin 20' of the transformer 1' is formed by two hole portions (a large hole portion 28L' and a small hole portion 28S) having different sizes. Further, the first bobbin 10 is held by the distal end portion 13a of the extending portion 13 inserted into the large-hole portion 28L' from the insertion opening 27' and then attached to the distal end portion 29 of the large-hole portion 28L'. 2 bobbin 20'.

1. . . Transformer (first embodiment)

1'. . . Transformer (variation of the first embodiment)

2. . . 1st winding (1 winding)

3. . . 2nd winding (2 windings)

4. . . Bobbin unit

5A, 5B. . . (first embodiment) core

6A to 6G. . . Terminal

7. . . Transformer (second embodiment)

8A, 8B. . . (second embodiment) core

9. . . Hold belt

10. . . First bobbin

11. . . First winding section

12. . . First through hole

13. . . Extension

13a. . . Front end face

14. . . Terminal block (of the first bobbin)

15A, 15B. . . End flange of the first bobbin

20, 20’. . . Second bobbin

twenty one. . . Second winding section

twenty two. . . Second through hole

23A, 23B. . . Terminal block (of the second bobbin)

24A, 24B. . . End of the second bobbin

25A, 25B. . . Separate flange

26A to 26E. . . Concave

27, 27’. . . Insert

28L, 28L’. . . Large hole

28M. . . Middle hole

28S. . . Small hole

29. . . Tail end

51A, 52A. . . (iron core 5A) foot

51B, 52B. . . (iron core 5B) foot

81A, 82A. . . (iron core 8A) outer leg

81B, 82B. . . (iron core 8B) outer leg

83A. . . Middle foot (core 8A)

83B. . . Midfoot (iron core 8B)

91. . . Base

92A to 92E. . . Claw

d ₁ , d ₂ . . . length

C ₁ , C ₂ . . . Axis

S ₁ to S ₃ . . . Winding area

Fig. 1 is a front elevational view showing the overall configuration of a transformer according to a first embodiment.

Fig. 2 is an exploded perspective view showing the transformer of the first embodiment.

Fig. 3 is a cross-sectional view taken along line A-A of Fig. 1 of the transformer of the first embodiment.

Figure 4 is an exploded view of the cross-sectional view shown in Figure 3.

Fig. 5 is a front elevational view showing the overall configuration of a transformer according to a second embodiment.

Fig. 6 is a perspective view showing a core and a holding belt used in the second embodiment.

Fig. 7 is a cross-sectional, exploded view of a transformer according to a modification of the first embodiment.

1. . . Transformer (first embodiment)

2. . . 1st winding (1 winding)

3. . . 2nd winding (2 windings)

4. . . Bobbin unit

5A, 5B. . . (first embodiment) core

6A to 6G. . . Terminal

10. . . First bobbin

11. . . First winding section

13. . . Extension

14. . . Terminal block (of the first bobbin)

15A, 15B. . . End flange of the first bobbin

20. . . Second bobbin

twenty one. . . Second winding section

23A, 23B. . . Terminal block (of the second bobbin)

24A, 24B. . . End of the second bobbin

25A, 25B. . . Separate flange

26A to 26E. . . Concave

52A. . . (iron core 5A) foot

52B. . . (iron core 5B) foot

Claims (6)

A transformer includes: a first winding; a second winding electromagnetically coupled to the first winding; and a first winding portion that winds the first winding and an inner portion that penetrates the first winding portion a first bobbin of the first through hole; a second bobbin having a second winding portion that winds the second winding and a second through hole that penetrates the inside of the second winding portion; and a second winding a core in the first through hole and the second through hole; and the first bobbin and the second bobbin are disposed coaxially; wherein the first bobbin is provided from the first One end portion of the winding portion in the axial direction extends toward the second bobbin, and has a hollow extending portion through which the iron core is inserted; and the second through hole of the second bobbin is attached to the second through hole One end portion of the hole in the axial direction is provided with an insertion port through which the extension portion is inserted, and a portion of a predetermined range extending from the insertion port toward the other end portion of the second through hole in the axial direction is formed as a large hole portion, and the large hole is formed The portion is formed to have a full circumference along the outer peripheral surface of the aforementioned extension portion inserted from the insertion port Air predetermined size interval. The transformer according to claim 1, wherein the second bobbin includes a partition flange for dividing the second winding portion into a plurality of winding regions. The transformer according to the first or second aspect of the invention, wherein the portion of the second through hole in the second bobbin is smaller than the large hole portion. a small hole portion having a size that allows the iron core to be inserted, and a portion between the small hole portion and the large hole portion is formed to have a size between the large hole portion and the small hole portion and formed It is a mesoporous portion of a size that can be fitted to the extension portion. A transformer includes: a first bobbin that winds a winding on an input side; a second bobbin that winds a winding on an output side; and a first winding that is inserted in a coaxial manner a through hole of the tube and an inner core of the through hole of the second bobbin; wherein one of the first bobbin and the second bobbin is tied to the other winding The side of the tube contact has an extension portion; at one end of the through hole of the other bobbin, an insertion port for inserting the extension portion is provided; and an inner circumference of the through hole of the other bobbin is extended with the extension The peripheral parts of the department are separated from each other by a certain distance. The transformer according to claim 4, wherein the second bobbin is provided with a partition flange for dividing a region around which the winding on the output side is wound into a plurality of partition flanges. The transformer of claim 4 or 5, wherein, in the through hole of the other bobbin, the portion on the side of the insertion port is formed to be spaced apart from the outer circumference of the extension portion. a large hole portion having a large distance, a portion on the opposite side of the insertion port is smaller than the large hole portion, and is formed in a small hole portion having a size in which the iron core can be inserted, and the small hole portion is The portion between the large hole portions is formed as a middle hole portion having a size that is large between the large hole portion and the small hole portion and that can be fitted to the extending portion.