Transformer

Abstract

A transformer (1) comprises: a first core (2) which has a base (2a) and a first outer magnetic limb (2b) and a second outer magnetic limb (2c) that are arranged side by side in a second direction (D2); an inner magnetic limb (3) which extends in a first direction (D1); an inner magnetic limb unit part (10) which has a sub core (11) that forms at least part of the inner magnetic limb (3), and which is separate from the first core (2); a main substrate (4), at least part of which is positioned between the first outer magnetic limb (2b) and the second outer magnetic limb (2c); a primary winding (5) which is provided to the main substrate (4) so as to surround the first outer magnetic limb (2b) on one side in the second direction (D2) with respect to the inner magnetic limb (3); and a secondary winding (6) which is provided on the main substrate (4) so as to surround the second outer magnetic limb (2c) on the other side in the second direction (D2) with respect to the inner magnetic limb (3).

Description

Transformer

[0001] The present invention relates to a transformer.

[0002] Patent Document 1 discloses a combined bobbin, a transformer, and a resonant converter. The transformer includes a combined bobbin, a primary winding, a secondary winding, and a core. The combined bobbin is composed of an upper bobbin, a lower bobbin, and a clamp member. The lower bobbin has a cylindrical portion, an upper flange portion, and a lower flange portion. The primary winding and the secondary winding are disposed in the cylindrical portion of the lower bobbin. A magnetic path is formed in the core between the primary winding and the secondary winding. The winding pitch between the primary winding and the secondary winding is the sum of the thicknesses of the upper flange portion and the lower flange portion.

[0003] Patent Document 2 discloses a planar transformer and a DC-DC converter. The planar transformer includes a primary-side planar air-core coil, a secondary-side planar air-core coil, a primary-side planar core, and a secondary-side planar core. The secondary-side planar air-core coil is disposed at an interval from the primary-side planar air-core coil in the winding central axis direction of the primary-side planar air-core coil. The primary-side planar core and the secondary-side planar core are laminated outside the primary-side planar air-core coil and the secondary-side planar air-core coil in the winding central axis direction.

[0004] Japanese Patent Application Laid-Open No. 2017-183524, Japanese Patent Application Laid-Open No. 2019-021733

[0005] In a transformer, a main magnetic flux that links both the primary winding and the secondary winding is formed. In addition to the main magnetic flux, a leakage magnetic flux that links one of the primary winding and the secondary winding and does not link the other may occur in the transformer. The leakage inductance caused by the leakage magnetic flux tends to be proportional to the distance between the primary winding and the secondary winding. In the above prior art, the distance between the primary winding and the secondary winding is changed by changing the thickness of the transformer member according to the applicable product of the transformer, and the leakage inductance is adjusted. Thus, there are cases where the thickness of the transformer member is designed each time according to the specifications of the applicable product of the transformer, and it may not be easy to adjust the leakage inductance.

[0006] The objective of the present invention is to provide a transformer that allows for easy adjustment of leakage inductance.

[0007] (1) A transformer according to one aspect of the present invention comprises a base, a first core having a first outer magnetic leg and a second outer magnetic leg extending from the base in a first direction and arranged side by side in a second direction intersecting the first direction, a middle magnetic leg unit portion which is separate from the first core and has a middle magnetic leg extending in a first direction and a subcore forming at least a part of the middle magnetic leg, a main substrate in which at least a part is located between the first outer magnetic leg and the second outer magnetic leg in a second direction, a primary winding provided on the main substrate surrounding the first outer magnetic leg on one side in the second direction relative to the middle magnetic leg, and a secondary winding provided on the main substrate surrounding the second outer magnetic leg on the other side in the second direction relative to the middle magnetic leg.

[0008] In the transformer described above, the main magnetic flux forms a magnetic path that travels from the first outer magnetic leg surrounded by the primary winding to the second outer magnetic leg surrounded by the secondary winding, and then back to the first outer magnetic leg. The middle magnetic leg of such a transformer functions as the portion through which the leakage magnetic flux passes. The leakage magnetic flux forms at least one magnetic path that travels from the first outer magnetic leg to the middle magnetic leg and then back to the first outer magnetic leg, or a magnetic path that travels from the second outer magnetic leg to the middle magnetic leg and then back to the second outer magnetic leg. The transformer is equipped with a middle magnetic leg unit section having a subcore that forms at least a part of the middle magnetic leg. With this configuration, the middle magnetic leg unit section can adjust at least one of the dimensions of the subcore in the first direction and the position of the subcore in the first direction relative to the main substrate. Therefore, the length of the member through which the leakage magnetic flux passes can be changed to any length, or the position of the member through which the leakage magnetic flux passes in the first direction can be changed to any position, or both. This makes it possible to adjust the leakage inductance. Therefore, without designing the transformer according to the specifications of the applicable product, the leakage inductance can be adjusted by adjusting at least one of the dimensions of the subcore in the first direction and the position of the subcore in the first direction relative to the main board. Thus, the leakage inductance of the transformer can be easily adjusted.

[0009] (2) In (1) above, the central magnetic leg unit has a sub-substrate on which the sub-core is mounted, and the sub-substrate may be attached to the main substrate. In such a configuration, the central magnetic leg unit can be detachably attached to the main substrate.

[0010] (3) In (2) above, the central magnetic leg has a main magnetic leg portion extending in a first direction from the base of the first core, and the subcore of the central magnetic leg unit portion may be positioned to overlap with the main magnetic leg portion in the first direction. In such a configuration, leakage flux can be passed through the main magnetic leg portion, and by attaching and detaching the central magnetic leg unit portion, the dimension of the central magnetic leg in the first direction can be set to either the combined length of the subcore and the main magnetic leg portion, or the length of the main magnetic leg portion.

[0011] (4) In (2) or (3) above, the central magnetic leg unit may have a positioning member interposed between the main board and the sub-board. In such a configuration, the positioning member determines the position of the sub-board in the first direction relative to the main board. Therefore, the position of the sub-core in the first direction relative to the main board can be adjusted by the positioning member. This makes it easy to adjust the leakage inductance of the transformer. Furthermore, by setting a desired distance between the main board and the sub-board and interposing a positioning member of a size corresponding to that distance between the main board and the sub-board, the sub-board can be easily attached to the main board. This makes it easy to position the sub-core relative to the main board.

[0012] (5) In (4) above, the positioning member may be made of resin. With such a configuration, electrical losses in the transformer due to heat generation from the positioning member can be suppressed. In addition, since magnetic flux passing through the positioning member can be suppressed, disturbances in the magnetic path of leakage flux can be suppressed. As a result, the desired output of the transformer can be maintained.

[0013] (6) In any of (1) to (5) above, the primary winding and secondary winding may be formed in advance as conductor patterns on the main substrate. In such a configuration, the structure of the primary winding and secondary winding can be simplified by forming them as conductor patterns on the main substrate, and manufacturing costs can be reduced.

[0014] (7) In any of (1) to (6) above, the transformer may further include a second core positioned opposite the base in the first direction, with the main substrate in between. In such a configuration, the main magnetic flux and leakage magnetic flux can pass through the second core. This makes it easier to form magnetic paths for the main magnetic flux and leakage magnetic flux in the transformer.

[0015] (8) In (7) above, an air gap may be formed between the central magnetic leg and the second core. In such a configuration, the air gap can be positioned away from the main substrate. Leakage flux tends to concentrate in the air gap, but by positioning the air gap away from the main substrate, the concentration of leakage flux can be separated from the primary and secondary windings provided on the main substrate. This can suppress heat generation in the transformer and reduce electrical losses.

[0016] (9) In the above (7) or (8), a support member may be further provided to support the first core and the second core by sandwiching them from a first direction. In such a configuration, since the support member supports the first core and the second core by sandwiching them, the shapes of the first core and the second core can be maintained, and a part of the first core and the second core can be protected by the support member.

[0017] According to the present invention, the leakage inductance of a transformer can be easily adjusted.

[0018] This is a side view showing a transformer according to the first embodiment of the present invention. This is a plan view showing the transformer excluding the I-core. This is a side view showing the magnetic flux lines in the transformer and an equivalent circuit diagram of the transformer. This is a side view showing the central magnetic leg unit. This is a side view showing a transformer according to a comparative example. This is a side view showing a transformer according to the second embodiment of the present invention. This is a side view showing a transformer according to the third embodiment of the present invention.

[0019] Embodiments of the present invention will be described in detail below with reference to the drawings. In the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0020] Figure 1 is a side view showing a transformer 1 according to a first embodiment of the present invention. The transformer 1 is assembled, for example, into a power conversion device. As shown in Figure 1, the transformer 1 comprises a first core 2, a central magnetic leg 3, a main substrate 4, a primary winding 5 and a secondary winding 6, a central magnetic leg unit 10, an I-core 7, and a support member 8.

[0021] In the following description, the first direction D1 is the direction in which the central magnetic leg 3 extends. The second direction D2 is the direction that intersects the first direction D1. In the following, as an example, the second direction D2 will be the direction in which the main substrate 4 extends.

[0022] The first core 2 is made of a magnetic material such as a magnet or ferrite, from the viewpoint of efficiently passing magnetic flux. By making the first core 2 of a magnetic material, it is possible to easily form magnetic paths for the main magnetic flux ΦM and leakage magnetic flux Φ, which will be described later, in the first core 2. The first core 2 has a base portion 2a, a first external magnetic leg 2b, and a second external magnetic leg 2c.

[0023] The base portion 2a is located on one side of the first core 2 in the first direction D1. The base portion 2a extends in the second direction D2. The base portion 2a has, for example, a rectangular parallelepiped shape. The length of the base portion 2a in the first direction D1 is shorter than the length of the base portion 2a in the second direction D2.

[0024] The base portion 2a is aligned with the main substrate 4, which will be described later. The base portion 2a faces the main substrate 4. The base portion 2a extends substantially parallel to the main substrate 4. "Substantially parallel" means not only the configuration in which the base portion 2a and the main substrate 4 are arranged parallel to each other, but also the configuration in which the base portion 2a extends at an angle to the main substrate 4.

[0025] The first external magnetic leg 2b and the second external magnetic leg 2c are arranged side by side in the second direction. The first external magnetic leg 2b and the second external magnetic leg 2c are located at the ends of the first core 2 in the second direction D2. The first external magnetic leg 2b and the second external magnetic leg 2c extend from the base 2a in the first direction D1. The first external magnetic leg 2b extends from one end of the base 2a in the second direction D2 to the first direction D1. The second external magnetic leg 2c extends from the other end of the base 2a in the second direction D2 to the first direction D1.

[0026] The first and second external magnetic legs 2b and 2c are, for example, rectangular parallelepipeds. The length of the first external magnetic leg 2b in the first direction D1 is longer than the length of the first external magnetic leg 2b in the second direction D2. The length of the second external magnetic leg 2c in the first direction D1 is longer than the length of the second external magnetic leg 2c in the second direction D2. The first and second external magnetic legs 2b and 2c may have the same shape as each other.

[0027] The central magnetic leg 3 is located inside the concave region formed by the first core 2. The central magnetic leg 3 is located in the central part of the first core 2 in the second direction D2. As mentioned above, the central magnetic leg 3 extends in the first direction D1. One end of the central magnetic leg 3 in the first direction D1 is adjacent to the base 2a.

[0028] The central magnetic leg 3 is positioned between the first external magnetic leg 2b and the second external magnetic leg 2c. The central magnetic leg 3 is sandwiched between the first external magnetic leg 2b and the second external magnetic leg 2c. In the second direction D2, the first external magnetic leg 2b, the central magnetic leg 3, and the second external magnetic leg 2c are arranged in order. The first external magnetic leg 2b, the central magnetic leg 3, and the second external magnetic leg 2c are arranged at equal intervals. However, the spacing between the first external magnetic leg 2b, the central magnetic leg 3, and the second external magnetic leg 2c may be uneven.

[0029] An E-core may be formed by the central magnetic leg 3 and the first core 2. In this case, the central magnetic leg 3 and the base 2a of the first core 2 may be integrally formed with each other. The central magnetic leg 3 is made of a magnetic material, similar to the first core 2, from the viewpoint of allowing the leakage flux Φ described later to pass through.

[0030] The central magnetic leg 3 has a main magnetic leg portion 3a. The main magnetic leg portion 3a extends from the base portion 2a of the first core 2 in a first direction D1. The main magnetic leg portion 3a is fixed to the base portion 2a. The main magnetic leg portion 3a may be integrally formed with the base portion 2a.

[0031] The main magnetic leg portion 3a is, for example, shaped like a rectangular parallelepiped. The length of the main magnetic leg portion 3a in the first direction D1 is the length between the base portion 2a and the main surface 4a (described later) of the main substrate 4. In the first direction D1, the length of the main magnetic leg portion 3a is shorter than the length of the first outer magnetic leg 2b and the length of the second outer magnetic leg 2c.

[0032] The main substrate 4 extends in the second direction D2. The main substrate 4 is located in the central part of the first core 2 in the first direction D1. Specifically, the main substrate 4 is located in the central part of the first outer magnetic leg 2b and the second outer magnetic leg 2c in the first direction D1. The main substrate 4 has a plate-like shape. The main substrate 4 may be formed by laminating multiple layers.

[0033] At least a portion of the main substrate 4 is located between the first external magnetic leg 2b and the second external magnetic leg 2c in the second direction D2. In this embodiment, the length of the main substrate 4 in the second direction D2 is longer than the distance between the first external magnetic leg 2b and the second external magnetic leg 2c. The main substrate 4 intersects with the first external magnetic leg 2b and the second external magnetic leg 2c. The first external magnetic leg 2b and the second external magnetic leg 2c penetrate the main substrate 4.

[0034] The main substrate 4 has a pair of through holes 4c (see Figure 2) arranged in the second direction D2. The through holes 4c have a rectangular cross-section that is large enough for the first outer magnetic leg 2b and the second outer magnetic leg 2c to pass through.

[0035] The main magnetic leg portion 3a of the central magnetic leg 3 penetrates the main substrate 4 in a first direction D1. The main substrate 4 has a through hole 4d (see Figure 2) in its center. The through hole 4d has a rectangular cross-section large enough for the main magnetic leg portion 3a to pass through. In this case, for example, the end face of the main magnetic leg portion 3a facing the first direction D1, opposite to the base portion 2a, may be flush with the main surface 4a of the main substrate 4. The central magnetic leg 3 may be fixed to the main substrate 4.

[0036] However, the main magnetic leg portion 3a of the central magnetic leg 3 does not have to penetrate the main substrate 4. In this case, the other end of the central magnetic leg 3 may be in contact with the main substrate 4. The other end of the central magnetic leg 3 is the end of the central magnetic leg 3 opposite to the base portion 2a of the first core 2. The main substrate 4 may be supported by the main magnetic leg portion 3a.

[0037] The main substrate 4 has main surfaces 4a and 4b. The main surfaces 4a and 4b face the first direction D1. Main surface 4a faces the opposite side of the base 2a of the first core 2 (towards the I core 7, which will be described later). Main surface 4b faces the base 2a side of the first core 2. The main surfaces 4a and 4b extend in a direction intersecting the direction in which the central magnetic leg 3 extends. In one example, the main surfaces 4a and 4b face in a direction perpendicular to the central magnetic leg 3.

[0038] The main substrate 4 is made of, for example, glass fiber reinforced epoxy resin (Flame Retardant Type 4). Hereinafter, the glass fiber reinforced epoxy resin will be referred to as FR4. By making the main substrate 4 out of FR4, the strength and electrical insulation of the main substrate 4 can be maintained.

[0039] The primary winding 5 and the secondary winding 6 are provided on the main substrate 4. The primary winding 5 and the secondary winding 6 are pre-formed as conductor patterns on the main surface 4a of the main substrate 4. However, the primary winding 5 and the secondary winding 6 may also be formed in the inner layers of the main substrate 4 if it has multiple layers.

[0040] By forming the primary winding 5 and secondary winding 6 on the main substrate 4, the design flexibility of the primary winding 5 and secondary winding 6 can be improved. Furthermore, the primary winding 5 and secondary winding 6 can be provided on the main substrate 4 at a low cost.

[0041] The central magnetic leg unit 10 is positioned in the first direction D1, aligned with the main magnetic leg portion 3a of the central magnetic leg 3. The I-core 7 is positioned in the first direction D1, aligned with the first core 2. The support member 8 supports the first core 2 and the I-core 7. The specific configurations of the central magnetic leg unit 10, the I-core 7, and the support member 8 will be described in detail later.

[0042] Figure 2 is a plan view showing the transformer 1 excluding the I-core 7 to be described later. The primary winding 5 is provided on one side of the middle magnetic leg 3 in the second direction D2 on the main substrate 4. The secondary winding 6 is provided on the other side of the middle magnetic leg 3 in the second direction D2 on the main substrate 4. The primary winding 5 and the secondary winding 6 are provided on the main substrate 4 apart from each other in the second direction D2.

[0043] The primary winding 5 is provided at a portion penetrated by the first outer magnetic leg 2b on the main substrate 4. The primary winding 5 surrounds the first outer magnetic leg 2b. The primary winding 5 is provided around the first outer magnetic leg 2b. The primary winding 5 has, for example, a shape wound a plurality of times along the main surface 4a of the main substrate 4 around the first outer magnetic leg 2b.

[0044] The secondary winding 6 is provided at a portion penetrated by the second outer magnetic leg 2c on the main substrate 4. The secondary winding 6 surrounds the second outer magnetic leg 2c. The secondary winding 6 is provided around the second outer magnetic leg 2c. The secondary winding 6 has, for example, a shape wound a plurality of times along the main surface 4a of the main substrate 4 around the second outer magnetic leg 2c. The direction in which the primary winding 5 is wound and the direction in which the secondary winding 6 is wound are opposite to each other.

[0045] The primary winding 5 has a spiral shape. The conductors constituting the primary winding 5 are arranged, for example, in different layers on the main substrate 4. Therefore, in the plan view of FIG. 2, at the portion where the conductors of the primary winding 5 seem to cross, the conductors do not contact each other and the primary winding 5 does not short-circuit. The same applies to the secondary winding 6.

[0046] FIG. 3(a) is a side view of the transformer 1 showing the magnetic flux lines in the transformer 1. In FIG. 3(a), the magnetic flux lines formed by the magnetic flux are illustrated. FIG. 3(b) is an equivalent circuit diagram showing the transformer 1. The equivalent circuit diagram of FIG. 3(b) corresponds to the side view of FIG. 3(a).

[0047] As shown in FIG. 3(a), in the transformer 1, a main magnetic flux ΦM that links both the primary winding 5 and the secondary winding 6 is formed. As shown in FIG. 3(b), an exciting inductance LM is generated by the main magnetic flux ΦM.

[0048] Also, as shown in Fig. 3(a), in the transformer 1, in addition to the main magnetic flux ΦM, there may be leakage fluxes that link to one of the primary winding 5 and the secondary winding 6 and do not link to the other of the primary winding 5 and the secondary winding 6.

[0049] For example, in the transformer 1, a primary leakage flux Φ1 that links to the primary winding 5 and does not link to the secondary winding 6 occurs, and a secondary leakage flux Φ2 that links to the secondary winding 6 and does not link to the primary winding 5 occurs. As shown in Fig. 3(b), the primary leakage inductance L1 is generated by the primary leakage flux Φ1. The secondary leakage inductance L2 is generated by the secondary leakage flux Φ2.

[0050] In the following description, when it is not necessary to particularly distinguish between the primary leakage flux Φ1 and the secondary leakage flux Φ2, these are collectively referred to as the leakage flux Φ. When it is not necessary to particularly distinguish between the primary leakage inductance L1 and the secondary leakage inductance L2, these are collectively referred to as the leakage inductance L. Incidentally, as shown in Fig. 3(b), an unintended parasitic capacitance C1 may occur between the primary winding 5 and the secondary winding 6.

[0051] When the inductance of the transformer 1 is large, the rate of change of the current passing through the transformer 1 can be reduced, and the peak value of the current can be reduced. Thereby, the power loss in the transformer 1 can be reduced, and the conversion efficiency of the transformer 1 can be improved. There is a need to adjust the inductance of the transformer 1 according to the specifications of the applied product of the transformer 1.

[0052] In a general E-core, the primary winding and the secondary winding may be arranged in a portion corresponding to the middle magnetic leg 3 of the present embodiment to form a transformer. Conventionally, the primary winding and the secondary winding may be arranged side by side in the first direction D1. In this case, for example, the leakage inductance L is adjusted by adjusting the arrangement interval of the primary winding and the secondary winding in the first direction D1. Alternatively, the leakage inductance L is adjusted by arranging the primary winding and the secondary winding offset from each other in the second direction D2.

[0053] However, when adjusting the spacing between the primary and secondary windings in the first direction D1, the dimensions of the components for arranging the primary and secondary windings may be designed each time to achieve the desired leakage inductance L, and multiple transformers may be manufactured accordingly. Furthermore, when arranging the primary and secondary windings offset from each other in the second direction D2, the range of adjustment may be limited because the primary and secondary windings must overlap when viewed from the first direction D1.

[0054] In this embodiment, the central magnetic leg 3 is not provided with a primary winding 5 and a secondary winding 6, and the central magnetic leg 3 functions as a part that forms the magnetic path of the primary leakage flux Φ1 and the secondary leakage flux Φ2. The central magnetic leg unit 10 provided in the transformer 1 of this embodiment is a member that deforms the shape of the central magnetic leg 3. The central magnetic leg unit 10 is separate from the first core 2.

[0055] Figure 4 is a side view showing the central magnetic leg unit 10. As shown in Figure 4, the central magnetic leg unit 10 has a subcore 11 and a sub-substrate 12. The sub-substrate 12 is a separate substrate from the main substrate 4.

[0056] The sub-substrate 12 has main surfaces 12a and 12b facing the first direction D1. The sub-core 11 is placed on the main surface 12a of the sub-substrate 12. The area of ​​the main surface 12a of the sub-substrate 12 is large enough to accommodate the sub-core 11.

[0057] Refer again to Figures 1 and 2. The sub-sub

[0058] The transformer 1 is equipped with screws N for fastening the main board 4 and the sub-board 12. The sub-board 12 is fixed to the main board 4 by screws N. The screws N are installed along the first direction D1. The screws N are screwed into the sub-board 12 from the side opposite to the base 2a of the first core 2, relative to both the sub-board 12 and the main board 4.

[0059] The screw N is made of, for example, resin. The resin material of the screw N helps to suppress the passage of leakage magnetic flux Φ through the screw. The transformer 1 is equipped with multiple screws N (four in this example). These multiple screws N are attached to the four corners of the sub-board 12.

[0060] The sub-board 12 can be attached to the main board 4 by the screw N, and the sub-board 12 can also be removed from the main board 4. In other words, the sub-board 12 is detachable from the main board 4. Therefore, the central magnetic leg unit 10 is detachable from the main board 4.

[0061] In the second direction D2, the length of the sub-substrate 12 is shorter than the length of the main substrate 4. In the second direction D2, the length of the sub-substrate 12 is longer than the length of the main magnetic leg portion 3a. The thickness of the sub-substrate 12 is approximately the same as the thickness of the main substrate 4.

[0062] The subcore 11 is a member that forms the central magnetic leg 3. The subcore 11 forms at least a part of the central magnetic leg 3. The subcore 11 forms the end of the central magnetic leg 3 opposite to the base 2a. The subcore 11 may form the entirety of the central magnetic leg 3. In this case, the central magnetic leg 3 does not need to have a main magnetic leg portion 3a.

[0063] The subcore 11 of the central magnetic leg unit 10 is positioned to overlap with the main magnetic leg portion 3a in the first direction D1. The subcore 11 and the main magnetic leg portion 3a are aligned in the first direction D1. The subcore 11 is made of the same material as, for example, the main magnetic leg portion 3a. Leakage flux Φ passes through the subcore 11.

[0064] The subcore 11 is, for example, rectangular parallelepiped. In the second direction D2, the length of the subcore 11 is, for example, the same as the length of the main magnetic leg portion 3a. In the second direction D2, the length of the subcore 11 is shorter than the length of the sub-substrate 12.

[0065] The subcore 11 is fixed to the main surface 12a of the sub-substrate 12. For example, the subcore 11 is fixed to the sub-substrate 12 such that the center line of the subcore 11 along the first direction D1 coincides with the center line of the main magnetic leg portion 3a along the first direction D1. The subcore 11 is firmly fixed to the main surface 12a of the sub-substrate 12 by an adhesive or the like.

[0066] The central magnetic leg unit 10 adjusts at least one of the dimensions A1 of the subcore 11 in the first direction D1 and the position of the subcore 11 in the first direction D1 relative to the main substrate 4. In this embodiment, the central magnetic leg unit 10 adjusts the dimension A1 of the subcore 11 in the first direction D1. Adjusting the dimension A1 of the subcore 11 means setting the dimension A1 of the subcore 11 to a desired dimension according to the specifications, etc.

[0067] In other words, adjusting the dimension A1 of the subcore 11 means setting the dimension A1 of the subcore 11 so that the desired leakage inductance L is obtained in the transformer 1. In the example in Figure 1, the dimension A1 of the subcore 11 is adjusted to be shorter than the length of the main magnetic leg portion 3a in the first direction D1.

[0068] The length B of the central magnetic leg 3 in the first direction D1 can be adjusted by adjusting the dimension A1 of the subcore 11. The length B of the central magnetic leg 3 in the first direction D1 is the length from the base 2a of the first core to the end face 11a of the subcore 11 that faces away from the sub-substrate 12.

[0069] By increasing the dimension A1 of the subcore 11 and thus increasing the length B of the central magnetic leg 3, the leakage inductance L of the transformer 1 can be increased. By decreasing the dimension A1 of the subcore 11 and thus decreasing the length B of the central magnetic leg 3, the leakage inductance L can be decreased. In other words, the leakage inductance L can be adjusted by adjusting the dimension A1 of the subcore 11 in the central magnetic leg unit 10.

[0070] Therefore, if multiple types of transformers with different specifications are manufactured, for example, multiple subcores 11 with different dimensions A1 in the first direction D1 may be manufactured and prepared in advance. However, the number of central magnetic leg units 10 assembled to the main board 4 is one.

[0071] By attaching a subcore 11 with a desired dimension A1 to a sub-substrate 12 to form a central magnetic leg unit 10, and then assembling the central magnetic leg unit 10 to the transformer 1, the dimension A1 of the subcore 11 can be adjusted, and consequently, the length B of the central magnetic leg 3 in the first direction D1 can be adjusted.

[0072] In this way, the leakage inductance L can be adjusted by adjusting the dimension A1 of the subcore 11 using the central magnetic leg unit 10. For example, for multiple application products of the transformer 1, each with different specifications, the structure of the main magnetic leg portion 3a of the transformer 1 is designed to be common, and the central magnetic leg unit 10, which is equipped with a subcore 11 having a dimension A1 that results in the desired leakage inductance L, is assembled to the transformer 1 according to the application product.

[0073] As a result, in the manufacturing of the first core 2 and the central magnetic leg 3, the main magnetic leg portion 3a can be designed in common, and in the manufacturing of the central magnetic leg unit portion 10, the specifications of the product to which the transformer 1 is applied can be taken into consideration. Thus, the versatility of the manufacturing of the transformer 1 can be improved.

[0074] Furthermore, the length B of the central magnetic leg 3 in the first direction D1 may be adjusted by attaching or detaching the central magnetic leg unit 10, thereby adjusting the leakage inductance L. That is, the leakage inductance L may be adjusted by assembling the central magnetic leg unit 10 to make the length B of the central magnetic leg 3 the combined length of the subcore 11 and the main magnetic leg 3a, or by removing (not mounting) the central magnetic leg unit 10 to make the length B of the central magnetic leg 3 the length of the main magnetic leg 3a.

[0075] Furthermore, as described above, the central magnetic leg 3 does not necessarily have a main magnetic leg portion 3a between the base portion 2a and the main substrate 4. By directly attaching the central magnetic leg unit portion 10 to the base portion 2a, the length B of the central magnetic leg 3 may be set to the length of the central magnetic leg unit portion 10 in the first direction D1. In this case, the dimension A1 of the subcore 11 can be adjusted in the same way as above. This makes it possible to adjust the length B of the central magnetic leg 3.

[0076] The sub-substrate 12 is made of the same material as the main substrate 4, for example. The sub-substrate 12 does not penetrate either the sub-core 11 or the main magnetic leg portion 3a. Therefore, the intermediate magnetic leg 3 is separated by the sub-substrate 12.

[0077] The dielectric constant of FR4 and other materials constituting the sub-substrate 12 is different from the dielectric constant of the magnetic materials constituting the sub-core 11 and the main magnetic leg portion 3a. The thickness of the sub-substrate 12 can be rephrased as the length of the gap in the central magnetic leg 3. For example, the leakage inductance L may be adjusted by changing the thickness of the sub-substrate 12.

[0078] The transformer 1 is equipped with an I-core 7 (second core). The I-core 7 is positioned opposite the base 2a in the first direction D1, with the main substrate 4 in between. The I-core 7 is positioned on the opposite side of the main substrate 4 from the base 2a. In the first direction D1, the I-core 7 is aligned with the first outer magnetic leg 2b, the middle magnetic leg 3, and the second outer magnetic leg 2c. The I-core 7 is in contact with the first outer magnetic leg 2b and the second outer magnetic leg 2c.

[0079] The I-core 7 extends in the second direction D2. The I-core 7 is, for example, rectangular. In the second direction D2, the length of the I-core 7 is approximately the same as the length of the first core 2. The I-core 7 functions as a magnetic path for the main magnetic flux ΦM and the leakage magnetic flux Φ (see Figure 3(a)). The EI core may be formed by the first core 2, the central magnetic leg 3 (E-core), and the I-core 7.

[0080] An air gap G is formed between the central magnetic leg 3 and the I-core 7. The air gap G is the gap between the end face 11a of the sub-core 11 and the I-core 7. The leakage inductance L can be adjusted by adjusting the dimension A1 of the sub-core 11, and the leakage inductance L can also be adjusted by adjusting the length of the air gap G.

[0081] Increasing the size of the air gap G can reduce the leakage inductance L. Increasing the size of the air gap G can increase the leakage inductance L. An air gap may also be formed between the first and second outer magnetic legs 2b and 2c and the I-core 7. A gap member may be interposed between the first and second outer magnetic legs 2b and 2c and the I-core 7.

[0082] The area separated by the I-core 7, the first core 2, and the central magnetic leg 3 is a space. However, this separated area may be filled with adhesive or the like. This may help maintain the shape of the transformer 1.

[0083] The transformer 1 is equipped with a support member 8. The support member 8 is a member that supports the first core 2 and the I-core 7 by sandwiching them from a first direction D1. The shape of the transformer 1 can be maintained by the support member 8. The support member 8 functions, for example, as a clip. The support member 8 is positioned at the ends of the first core 2 and the I-core 7 in the second direction D2.

[0084] The transformer 1 is equipped with multiple sets (two sets in one example) of support members 8. The multiple support members 8 are arranged in the second direction D2. The multiple sets of support members 8 are arranged symmetrically with respect to the central magnetic leg 3.

[0085] The support member 8 has a fixing portion 8a and a support portion 8b. The fixing portion 8a is a member that fixes the support portion 8b to the main substrate 4. The fixing portion 8a may be, for example, a screw. The support member 8 has a pair of fixing portions 8a and a pair of support portions 8b. The pair of fixing portions 8a fix the support portion 8b to the main substrate 4 in the first direction D1.

[0086] The support portion 8b is made of, for example, metal, to ensure rigidity as a clip. The support portion 8b may also function as a spring. A portion between one end of the support portion 8b and the other end of the support portion 8b is V-shaped.

[0087] One end of a pair of support parts 8b is in contact with the surface of the I-core 7 facing away from the main substrate 4. The other end of one of the pair of support parts 8b is fixed to the main substrate 4 via a fixing part 8a. The other end of the pair of support parts 8b is in contact with the surface of the base 2a of the first core 2 facing away from the main substrate 4. The other end of the pair of support parts 8b is fixed to the main substrate 4 via a fixing part 8a.

[0088] Figure 5 is a side view showing a transformer 1X according to a comparative example. Transformer 1X does not have a central magnetic leg unit 10. Furthermore, transformer 1X has an E-core 2X having a central magnetic leg 3X, a base portion 2a, a first outer magnetic leg 2b, and a second outer magnetic leg 2c. In these respects, transformer 1X differs from transformer 1 of the first embodiment.

[0089] In transformer 1X, the dimension of the central magnetic leg 3X in the first direction D1 is the length between the base 2a and the end face 3b of the main magnetic leg 3a facing the I-core 7. In transformer 1X, an air gap G is formed between the end face 3b of the main magnetic leg 3a and the I-core 7. In conventional E-core 2X, the dimension of the central magnetic leg 3X in the first direction D1 is fixed, and in order to adjust the leakage flux Φ, it is necessary to manufacture multiple transformers 1X equipped with central magnetic legs 3X having different dimensions in the first direction D1, which can make it difficult to adjust the leakage inductance L.

[0090] In contrast, in the transformer 1 of this embodiment, the main magnetic flux ΦM forms a magnetic path that goes from the first outer magnetic leg 2b surrounded by the primary winding 5 to the second outer magnetic leg 2c surrounded by the secondary winding 6, and then returns to the first outer magnetic leg 2b. The middle magnetic leg 3 of such a transformer 1 functions as the portion through which the leakage magnetic flux Φ passes. The leakage magnetic flux Φ forms at least a magnetic path (primary leakage magnetic flux Φ1) that goes from the first outer magnetic leg 2b to the middle magnetic leg 3 and then returns to the first outer magnetic leg 2b, or a magnetic path (secondary leakage magnetic flux Φ2) that goes from the second outer magnetic leg 2c to the middle magnetic leg 3 and then returns to the second outer magnetic leg 2c. The transformer 1 is equipped with a middle magnetic leg unit section 10 having a subcore 11 that forms at least a part of the middle magnetic leg 3. With this configuration, the dimension A1 in the first direction D1 of the subcore 11 can be adjusted by the middle magnetic leg unit section 10. Therefore, the length of the member through which the leakage magnetic flux Φ passes can be changed to any length. This makes it possible to adjust the leakage inductance L. Therefore, the leakage inductance L of the transformer 1 can be adjusted by adjusting the dimension (length B) of the first direction D1 of the central magnetic leg 3, without having to design the transformer 1 according to the specifications of the product to which it is applied, such as a charger. Thus, the leakage inductance L of the transformer 1 can be easily adjusted.

[0091] Furthermore, although the specifications such as rated power, voltage, and current differ for the various application products of transformer 1, the leakage inductance L of transformer 1 can be easily adjusted to match the specifications of the application product by adjusting the length B of the first direction D1 of the central magnetic leg 3, thereby increasing the product configuration of transformer 1 at low cost.

[0092] Furthermore, in this embodiment, the primary winding 5 and the secondary winding 6 are provided on the main substrate 4, separated from each other in the second direction D2. The primary winding 5 and the secondary winding 6 are provided so as not to overlap in the first direction D1. As a result, the primary winding 5 and the secondary winding 6 are separated from each other, which weakens the electric field between the primary winding 5 and the secondary winding 6, and reduces the value of the parasitic capacitance C1 that occurs between the primary winding 5 and the secondary winding 6. Since the parasitic capacitance C1 is proportional to the reciprocal of the distance between the primary winding 5 and the secondary winding 6, the value of the parasitic capacitance C1 can be reduced by increasing this distance. Therefore, the conversion efficiency of the transformer 1 can be maintained.

[0093] Furthermore, in this embodiment, the central magnetic leg unit 10 has a sub-substrate 12 on which the sub-core 11 is mounted, and the sub-substrate 12 is attached to the main substrate 4. With this configuration, the central magnetic leg unit 10 can be detachably attached to the main substrate 4.

[0094] Furthermore, in this embodiment, the central magnetic leg 3 has a main magnetic leg portion 3a extending in a first direction D1 from the base portion 2a of the first core 2, and the subcore 11 of the central magnetic leg unit portion 10 is positioned to overlap with the main magnetic leg portion 3a in the first direction D1. In this configuration, leakage flux Φ can be passed through the main magnetic leg portion 3a, and by attaching and detaching the central magnetic leg unit portion 10, the length B of the central magnetic leg 3 in the first direction D1 can be set to either the combined length of the subcore 11 and the main magnetic leg portion 3a, or the length of the main magnetic leg portion 3a.

[0095] Furthermore, in this embodiment, the transformer 1 is equipped with screws N that fasten the main board 4 and the sub-board 12 together. The screws N may be made of resin. With this configuration, electrical losses in the transformer 1 due to heat generation from the screws N can be suppressed. In addition, since magnetic flux passing through the screws N can be suppressed, disturbances in the magnetic path of leakage flux Φ can be suppressed. As a result, the desired output of the transformer 1 can be maintained.

[0096] Furthermore, in this embodiment, the primary winding 5 and the secondary winding 6 are pre-formed as conductor patterns on the main substrate 4. With this configuration, since the primary winding 5 and the secondary winding 6 are formed as conductor patterns on the main substrate 4, the structure of the primary winding 5 and the secondary winding 6 can be simplified, and manufacturing costs can be reduced.

[0097] Furthermore, in this embodiment, the transformer 1 includes an I-core 7 positioned opposite the base 2a and the first direction D1, with the main substrate 4 in between. In this configuration, the main magnetic flux ΦM and the leakage magnetic flux Φ can pass through the I-core 7. This makes it easier to form magnetic paths for the main magnetic flux ΦM and the leakage magnetic flux Φ in the transformer 1.

[0098] Furthermore, in this embodiment, an air gap G is formed between the central magnetic leg 3 and the I-core 7. In this configuration, the position of the air gap G can be separated from the main substrate 4. Although leakage flux Φ tends to concentrate in the air gap G, by separating the position of the air gap G from the main substrate 4, the concentration of leakage flux Φ can be separated from the primary winding 5 and secondary winding 6 provided on the main substrate 4. As a result, heat generation in the transformer 1 can be suppressed and electrical losses can be reduced.

[0099] Furthermore, in this embodiment, the transformer 1 is provided with a support member 8 that supports the first core 2 and the I-core 7 by sandwiching them from a first direction D1. In this configuration, since the support member 8 supports the first core 2 and the I-core 7 by sandwiching them, the shapes of the first core 2 and the I-core 7 can be maintained, and a portion of the first core 2 and the I-core 7 can be protected by the support member 8.

[0100] Figure 6 is a side view showing a transformer 1A according to a second embodiment of the present invention. The central magnetic leg 3A of the transformer 1A according to the second embodiment differs from that of the transformer 1 in that the dimension A2 of the subcore 11A in the first direction D1 is shorter than the dimension A1 of the subcore 11 of the transformer 1 of the first embodiment.

[0101] The central magnetic leg unit 10 of the transformer 1A has a subcore 11A. As described above, in the central magnetic leg unit 10, a subcore with a desired size can be placed on the sub-substrate 12 from among a plurality of subcores (for example, subcore 11 and subcore 11A) that have different dimensions in the first direction D1 from each other.

[0102] Furthermore, since the central magnetic leg unit 10 is detachable from the transformer, the length B of the central magnetic leg in the transformer can be adjusted by assembling the central magnetic leg unit 10, which has a subcore of the desired dimensions mounted on the sub-substrate 12, onto the main substrate 4.

[0103] In the transformer 1A according to the second embodiment, the same effects as the transformer 1 of the first embodiment can be obtained.

[0104] Figure 7 is a side view showing a transformer 1B according to a third embodiment of the present invention. In Figure 7, a gap member (not shown) is interposed between the first and second outer magnetic legs 2b and 2c of the first core 2 and the I-core 7. The gap member fixes the first outer magnetic leg 2b and the I-core 7 to each other. Similarly, the gap member fixes the second outer magnetic leg 2c and the I-core 7 to each other.

[0105] The central magnetic leg unit 10 of the transformer 1B in the third embodiment differs from the transformer 1 of the first embodiment in that it has a positioning member 20. The positioning member 20 is interposed between the main substrate 4 and the sub-substrate 12. The positioning member 20 is made of, for example, resin.

[0106] As described above, the central magnetic leg unit 10 adjusts at least one of the dimension A1 of the subcore 11 in the first direction D1 and the position of the subcore 11 in the first direction D1 relative to the main substrate 4. In the third embodiment, the central magnetic leg unit 10 adjusts the position C of the subcore 11 in the first direction D1 relative to the main substrate 4. The position C of the subcore 11 will be described in detail later.

[0107] The positioning member 20 includes a spacer S and a screw N. The spacer S determines the position of the sub-sub

[0108] The transformer 1B is equipped with multiple (four in one example) cylindrical spacers S. For example, the multiple spacers S are arranged at the four corners of the sub-board 12. In the second direction D2, the spacing between the multiple spacers S is wider than the length of the main magnetic leg portion 3a and the length of the sub-core 11.

[0109] The dimensions of the spacer S in the first direction D1 are the length between the main surface 4a of the main substrate 4 and the main surface 12b of the sub-substrate 12. An air gap G is formed between the main surface 4a of the main substrate 4 and the main surface 12b of the sub-substrate 12.

[0110] A screw N is screwed into the inside of the spacer S. The screw N fastens the main board 4 and the sub-board 12 together, as in the first embodiment. The position of the sub-board 12 in the first direction D1 relative to the main board 4 is determined by the spacer S, and then by screwing the screw N into the inside of the spacer S, it is easy to form an air gap G of the desired size, and the sub-board 12 can be easily fixed to the main board 4.

[0111] Furthermore, by tightening the screw N into the spacer S from the first direction D1, a positioning member 20 can be formed in which the spacer S and the screw N are integrated. This makes the positioning member 20 more compact.

[0112] By replacing the spacer S with one having the desired dimensions in the first direction D1, the position of the sub-board 12 in the first direction D1 relative to the main board 4 can be adjusted. The position C of the sub-core 11 in the first direction D1 relative to the main board 4 can also be adjusted using the spacer S.

[0113] The position C of the subcore 11 in the first direction D1 relative to the main substrate 4 refers, for example, to the position of the end face 11a of the subcore 11 relative to the main surface 4a of the main substrate 4. In the third embodiment, adjusting the position C of the subcore 11 means adjusting the position of the end face 11a of the subcore 11 relative to the main surface 4a of the main substrate 4.

[0114] In other words, adjusting the position C of the subcore 11 means adjusting the dimension of the spacer S in the first direction D1. This allows for adjustment of the dimensions of the air gap G and the position C of the subcore 11. By adjusting the dimensions of the air gap G and the position C of the subcore 11, the desired leakage inductance L can be adjusted in the transformer 1B.

[0115] As in the third embodiment, the dimension A1 of the subcore 11 is fixed, and the leakage inductance L can be adjusted by adjusting the position C of the subcore 11 in the first direction D1 relative to the main substrate 4 using a spacer S. In this case, the leakage inductance L can be adjusted more easily than by replacing it with a subcore 11 of a different dimension.

[0116] In the third embodiment, the end face 11a of the subcore 11 is in contact with the I-core 7. The dimension A1 of the subcore 11 in the third embodiment is the same as the dimension A1 of the subcore 11 in the first embodiment.

[0117] However, in the third embodiment, the dimension A1 of the subcore 11 may be adjusted. In this case, the leakage inductance L may be adjusted by adjusting both the position C of the subcore 11 in the first direction D1 relative to the main substrate 4 and the dimension A1 of the subcore 11 in the first direction D1.

[0118] As described above, in this embodiment, the central magnetic leg unit 10 allows adjustment of the position C of the subcore 11 in the first direction D1 relative to the main substrate 4. Therefore, the position C of the member through which the leakage flux Φ passes in the first direction D1 can be changed to any position. This allows adjustment of the leakage inductance L. Thus, the leakage inductance L can be adjusted by adjusting the position C of the subcore 11 in the first direction D1 relative to the main substrate 4, without having to design the transformer 1 according to the specifications of the applicable product. Consequently, the leakage inductance L of the transformer 1 can be easily adjusted.

[0119] Furthermore, in this embodiment, the transformer 1B includes a positioning member 20 interposed between the main substrate 4 and the sub-sub

[0120] Furthermore, by setting a desired distance between the main board 4 and the sub-board 12, and interposing a positioning member 20 with dimensions corresponding to that distance between the main board 4 and the sub-board 12, the sub-board 12 can be easily attached to the main board 4. This facilitates the positioning of the sub-core 11 relative to the main board 4.

[0121] Furthermore, in this embodiment, the positioning member 20 is made of resin. With this configuration, electrical losses in the transformer 1B due to heat generation from the positioning member 20 can be suppressed. In addition, since magnetic flux passing through the positioning member 20 can be suppressed, disturbances in the magnetic path of leakage flux Φ can be suppressed. As a result, the desired output of the transformer 1B can be maintained.

[0122] Although several embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, in the above embodiments, the central magnetic leg unit 10 adjusts at least one of the dimensions of the subcore 11 in the first direction D1 and the position C of the subcore 11 in the first direction D1 relative to the main substrate 4, but the invention is not limited to such a form. For example, the central magnetic leg unit 10 may adjust both the dimensions of the subcore 11 in the first direction D1 and the position C of the subcore 11 in the first direction D1 relative to the main substrate 4.

[0123] Furthermore, in the above embodiment, the central magnetic leg 3 is located in the central part of the first core 2, but the embodiment is not limited to this configuration. For example, the central magnetic leg 3 may be positioned to one side of the second direction D2.

[0124] Furthermore, in the above embodiment, the length of the main magnetic leg portion 3a in the first direction D1 is the length between the base portion 2a of the first core 2 and the main surface 4a of the main substrate 4, but the embodiment is not limited to this. For example, the length of the main magnetic leg portion 3a in the first direction D1 may be the length from the base portion 2a to just before the main substrate 4. In this case, an air gap may be formed between the main magnetic leg portion 3a and the main substrate 4. The leakage inductance L can also be adjusted by adjusting the length of the air gap.

[0125] Furthermore, in the above embodiment, an air gap G is formed between the subcore 11 and the I-core 7, and the sub-substrate 12 is in contact with the main substrate 4, but the embodiment is not limited to this configuration. For example, the sub-substrate 12 may be positioned away from the main substrate 4. In this case, an air gap may also be formed between the sub-substrate 12 and the main substrate 4.

[0126] Furthermore, in the above embodiment, the primary winding 5 and the secondary winding 6 are formed in advance as conductor patterns on the main surface 4a of the main substrate 4, but the embodiment is not limited to this configuration. For example, the primary winding 5 and the secondary winding 6 may be arranged on the main surface 4a of the main substrate 4. In this case, the primary winding and the secondary winding may be placed on the main surface 4a of the main substrate 4 as a Litz wire. A Litz wire is a winding formed by bundling multiple conductors together. A Litz wire can reduce, for example, the loss of high-frequency current.

[0127] Furthermore, in the above embodiment, the positioning member 20 has a spacer S and a screw N, but it is not limited to such a configuration. For example, the positioning member 20 may have only a spacer S, or it may have only a screw N.

[0128] Furthermore, in the above embodiment, the positioning member 20 is interposed between the main substrate 4 and the sub-sub

[0129] Furthermore, in the above embodiment, the positioning member 20 is interposed between the main substrate 4 and the sub-substrate 12, but the configuration is not limited to this. For example, the positioning member 20 may be interposed between the main substrate 4 and the sub-core 11. In this case, the transformer 1B does not need to be provided with the sub-substrate 12.

[0130] 1, 1A, 1B Transformer 2 First core 2a Base 2b First outer magnetic leg 2c Second outer magnetic leg 3, 3A Middle magnetic leg 3a Main magnetic leg section 4 Main substrate 5 Primary winding 6 Secondary winding 7 I-core (second core) 8 Support member 10 Middle magnetic leg unit section 11, 11A Sub-core 12 Sub-sub substrate 20 Positioning member A1, A2 Dimensions C Position D1 First direction D2 Second direction G Air gap

Claims

1. A transformer comprising: a base portion; a first core having a base portion; a first outer magnetic leg and a second outer magnetic leg extending from the base portion in a first direction and arranged side by side in a second direction intersecting the first direction; a middle magnetic leg unit portion having a middle magnetic leg extending in the first direction and a subcore forming at least a part of the middle magnetic leg, and being separate from the first core; a main substrate having at least a part of which is located between the first outer magnetic leg and the second outer magnetic leg in the second direction; a primary winding provided on the main substrate surrounding the first outer magnetic leg on one side in the second direction relative to the middle magnetic leg; and a secondary winding provided on the main substrate surrounding the second outer magnetic leg on the other side in the second direction relative to the middle magnetic leg.

2. The transformer according to claim 1, wherein the central magnetic leg unit portion has a sub-substrate on which the sub-core is mounted, and the sub-sub-substrate is attached to the main substrate.

3. The transformer according to claim 2, wherein the central magnetic leg has a main magnetic leg portion extending in a first direction from the base portion of the first core, and the subcore of the central magnetic leg unit portion is positioned to overlap with the main magnetic leg portion in a first direction.

4. The transformer according to claim 2, wherein the central magnetic leg unit portion has a positioning member interposed between the main substrate and the sub-substrate.

5. The transformer according to claim 4, wherein the positioning member is made of resin.

6. The transformer according to claim 1, wherein the primary winding and the secondary winding are formed in advance as a conductor pattern on the main substrate.

7. The transformer according to claim 1, further comprising a second core arranged so as to face the base portion in the first direction, with the main substrate in between.

8. The transformer according to claim 7, wherein an air gap is formed between the central magnetic leg and the second core.

9. The transformer according to claim 7, further comprising a support member that sandwiches and supports the first core and the second core from a first direction.

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