Transformer

Abstract

To provide a versatile transformer capable of freely adjusting leakage inductance while suppressing volume change.SOLUTION: A transformer 1 includes a first bobbin 10 having a first cylindrical portion 11, a first winding 20 wound around the first cylindrical portion 11, a second bobbin 30 having a second cylindrical portion 31 and assembled to the first bobbin 10 such that the second cylindrical portion 31 overlaps the first cylindrical portion 11 in the radial direction of the first cylindrical portion 11, a second winding 40 wound around the second cylindrical portion 31, and a core 2 inserted through the first and second cylindrical portions 11 and 31, the first bobbin 10 includes a central collar portion 12c that divides the first cylindrical portion 11 into an overlapping portion 111 radially overlapping the second cylindrical portion 31 and a non-overlapping portion 112 not radially overlapping the second cylindrical portion 31 in the axial direction. The first bobbin 10 is configured such that the first winding 20 can be wound such that the thickness of the first cylindrical portion 11 in the radial direction increases in the non-overlapping portion 112 rather than the overlapping portion 111 in the first cylindrical portion 11.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] This invention relates to a transformer.

Background Art

[0002] Patent Document 1 discloses a transformer in which a primary winding and a secondary winding are wound around a core, and the primary winding has a portion (overlapping portion) that overlaps with the secondary winding and a portion (non-overlapping portion) that does not overlap with the secondary winding. In the transformer of Patent Document 1, the leakage inductance in the transformer is adjusted by adjusting the winding width and the number of turns of the primary winding.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the transformer (device) of Patent Document 1, the diameter dimensions (outer diameter dimension and inner diameter dimension) of the cylindrical primary winding and secondary winding are each constant in the axial direction. For this reason, in order to adjust the leakage inductance in the transformer, it is necessary to change the diameter dimensions of the primary winding and the secondary winding. Therefore, depending on the adjustment of the leakage inductance, the axial dimension and the radial dimension of the transformer change greatly. That is, the volume change of the transformer becomes large depending on the adjustment of the leakage inductance. For this reason, for example, when the volume of the transformer is limited due to the relationship with other components, in the conventional transformer, the leakage inductance cannot be freely adjusted, and it lacks versatility.

[0005] In view of the above problems, an object of the present invention is to provide a transformer with excellent versatility that can freely adjust the leakage inductance while suppressing a small volume change.

Means for Solving the Problem

[0006] One aspect of the present invention includes a first bobbin having a first cylindrical portion, a first winding wound around the first cylindrical portion, a second bobbin having a second cylindrical portion, and the second cylindrical portion being assembled to the first bobbin so as to overlap the first cylindrical portion in the radial direction of the first cylindrical portion, a second winding wound around the second cylindrical portion, and a core inserted through the first and second cylindrical portions. In a state where the second bobbin is assembled, the first bobbin has a wall portion that axially divides the first cylindrical portion into an overlapping portion that overlaps the second cylindrical portion in the radial direction and a non-overlapping portion that does not overlap the second cylindrical portion in the radial direction. The first bobbin is configured such that the first winding can be wound around the non-overlapping portion of the first cylindrical portion so that the radial thickness of the first cylindrical portion becomes larger than that of the overlapping portion. The second bobbin is assembled so as to be axially relatively movable with respect to the first bobbin in the axial direction of the first cylindrical portion, and is assembled radially inward of the overlapping portion in the first cylindrical portion. It is a transformer.

Advantages of the Invention

[0007] In the transformer of the present invention, the first bobbin is configured such that the first winding can be wound around the non-overlapping portion so that the radial thickness becomes larger than that of the overlapping portion. Thereby, the manufacturer can change the radial thickness of the first winding in the non-overlapping portion without changing the radial thickness of the first winding in the overlapping portion. For this reason, the manufacturer can adjust the leakage inductance without changing the radial thickness of the second winding that overlaps the overlapping portion in the radial direction. By changing the radial thickness of the first winding in the non-overlapping portion, the change in the radial volume of the first winding and the second winding can be suppressed to be smaller than the case where the radial thicknesses of the first winding and the second winding in the overlapping portion are changed. Further, in a state where the second bobbin is assembled, the first bobbin has a wall portion that axially divides the first cylindrical portion into an overlapping portion and a non-overlapping portion. Thereby, the manufacturer can axially divide the first winding into an overlapping winding that overlaps the second winding in the radial direction and a non-overlapping winding that does not overlap the second winding in the radial direction by simply assembling the first bobbin and the second bobbin. Therefore, the manufacturer can more easily form the overlapping winding and the non-overlapping winding as compared with the case where the wall portion is not provided on the first bobbin. Thus, the manufacturer can easily adjust the radial thickness, the axial length, etc. of the first winding at each of the overlapping portion and the non-overlapping portion. Therefore, it is possible to provide a transformer excellent in versatility that can freely adjust the leakage inductance while suppressing a small change in volume.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0009] Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 8. As shown in FIGS. 1 to 3, the transformer 1 according to this embodiment includes a core 2, a first bobbin 10, a first winding 20, a second bobbin 30, a second winding 40, a cover component 3, and a terminal block 8. The transformer 1 obtains the function of a resonant coil by utilizing the leakage inductance generated between the first winding 20 and the second winding 40.

[0010] The core 2 is formed of a magnetic material such as ferrite, for example. As shown in FIG. 2, the core 2 is formed of two core pieces 50. Since the two core pieces 50 are substantially the same, only one of the core pieces 50 will be described. The core piece 50 has an inner piece 51 formed in a columnar shape, two outer pieces 52 disposed on both sides in the radial direction with respect to the inner piece 51, and a connecting piece 53 connecting the two outer pieces 52 in the radial direction. The axial length of the inner piece 51 is longer in the core piece 50 on the first bobbin 10 side, which will be described later, among the two core pieces 50. In the following description, the axial direction of the inner piece 51 will simply be referred to as the "axial direction", the radial direction of the inner piece 51 will simply be referred to as the "radial direction", and the circumferential direction of the inner piece 51 will simply be referred to as the "circumferential direction". In the schematic diagram of FIG. 3, for simplicity, the pair of inner pieces 51 are integrated and simply illustrated as the core 2. Each of the two outer pieces 52 is formed in a rectangular plate shape with the thickness direction coinciding with the radial direction. The two outer pieces 52 are spaced apart on both sides of the inner piece 51 in the radial direction. The connecting piece 53 is formed in a rectangular plate shape with the thickness direction coinciding with the axial direction. The axial length of the outer piece 52 is longer in the core piece 50 on the first bobbin 10 side, which will be described later, among the two core pieces 50. The connecting piece 53 is formed in a rectangular plate shape with its thickness direction coinciding with the axial direction. The axial end of the inner piece 51 is continuous with the connecting piece 53. A recess 53a is formed in one end face of the connecting piece 53 in the direction facing the outer piece 52 and in a direction orthogonal to the axial direction. The recess 53a is formed in a tapered shape that widens as it goes from its bottom 53a2 toward the end face of the connecting piece 53 where the recess 53a opens. The recess 53a has a flat bottom 53a2 and two flat side portions 53a1 that extend inclined from both sides of the bottom 53a2 to the end face of the connecting piece 53. The core 2 is formed by abutting the axial tips of the outer pieces 52 of the two core pieces 50 described above and joining them with an adhesive or the like.

[0011] The first bobbin 10 is formed of an insulating material such as hard plastic, for example. The first bobbin 10 has a first cylindrical portion 11 and a first flange portion 12. The first cylindrical portion 11 is formed in a cylindrical shape. The inner diameter dimension of the first cylindrical portion 11 is larger than the outer diameter dimension of the core 2. The inner piece 51 of the core 2 is inserted inside the first cylindrical portion 11.

[0012] The first flange portion 12 has an end flange portion 12b disposed at one axial end 11b of the first cylindrical portion 11 and a central flange portion 12c (corresponding to the "wall portion" in the claims) disposed at the central portion 11c in the axial direction of the first cylindrical portion 11. The end flange portion 12b and the central flange portion 12c each project radially outward from the outer peripheral surface of the first cylindrical portion 11. In the following description, in the first cylindrical portion 11, the region on the opposite side of the end flange portion 12b in the axial direction with respect to the central flange portion 12c is defined as the overlapping portion 111, and the region between the end flange portion 12b and the central flange portion 12c is defined as the non-overlapping portion 112. A passage connecting the overlapping portion 111 and the non-overlapping portion 112 is formed in a part of the circumferential direction of the first cylindrical portion 11 around the central flange portion 12c. As shown in FIG. 3, the first flange portion 12 may have, in addition to the end flange portion 12b and the central flange portion 12c, an other-end flange portion 12a disposed at the other axial end 11a of the first cylindrical portion 11.

[0013] The first winding 20 is an input-side primary winding connected to a power supply circuit (not shown). The first winding 20 is formed by winding a wire around the outer peripheral surface of the first cylindrical portion 11 in its circumferential direction. That is, the first winding 20 is formed in a cylindrical shape by being wound around the core 2 via the first bobbin 10. In the following description, among the first winding 20, the portion wound around the overlapping portion 111 is referred to as the overlapping winding 21, and the portion wound around the non-overlapping portion 112 is referred to as the non-overlapping winding 22. The wire of the first winding 20 is a litz wire formed by twisting a plurality of enameled wires.

[0014] The overlapping winding 21 and the non-overlapping winding 22 are adjacent to each other in the axial direction. The thickness of the non-overlapping winding 22 in the radial direction is larger than the thickness of the overlapping winding 21 in the radial direction. The non-overlapping winding 22 and the overlapping winding 21 are connected by the wire of the first winding 20 passing through a passage provided in the central flange portion 12c.

[0015] The first winding 20 forms a base layer 23 by winding the wire around the overlapping portion 111 and the non-overlapping portion 112 at least one layer each. In FIG. 3, an example is illustrated in which the wire is wound around the overlapping portion 111 and the non-overlapping portion 112 one layer each to form the base layer 23, but the base layer 23 may be formed by winding the wire two or more layers. Note that the number of layers of the base layer 23 may be different between the overlapping portion 111 and the non-overlapping portion 112.

[0016] Both ends of the wire of the first winding 20 described above are connected to a first terminal 5a and a second terminal 5b (see FIGS. 4 to 8). The first and second terminals 5a, 5b are terminals for connecting the first winding 20 to the power supply circuit, and are arranged at positions corresponding to one end flange portion 12b of the first bobbin 10 (the fourth portion 2d of the core 2 described later). The first and second terminals 5a, 5b may be provided, for example, on the one end flange portion 12b of the first bobbin 10.

[0017] The second bobbin 30 is formed of an insulating material such as hard plastic. The second bobbin 30 is disposed radially outside the overlapping portion 111 in the first cylindrical portion 11. The second bobbin 30 is assembled to be axially slidable and relatively movable with respect to the first bobbin 10. The second bobbin 30 has a second cylindrical portion 31 and a second flange portion 32. An inner piece 51 of the core 2 is inserted inside the second cylindrical portion 31. The inner diameter dimension of the second cylindrical portion 31 is larger than the outer diameter dimension of the overlapping portion 111 in the first cylindrical portion 11. The radial separation distance between the second cylindrical portion 31 and the first cylindrical portion 11 is equal to or greater than twice the diameter dimension of the wire of the first winding 20.

[0018] The second flange portion 32 (one - end flange portion 32b) is provided at one end 31b on the side of the central flange portion 12c among the axial both ends 31a, 31b of the second cylindrical portion 31. The second flange portion 32 projects radially outward from the second cylindrical portion 31. As shown in FIG. 3, the second flange portion 32 may have, in addition to the one - end flange portion 32b, the other - end flange portion 32a disposed at the other axial end 31a of the second cylindrical portion 31.

[0019] The second winding 40 is an output - side secondary winding connected to a load device (not shown). The second winding 40 is formed by winding a wire around the outer peripheral surface of the second cylindrical portion 31 in its circumferential direction. That is, the second winding 40 is formed in a cylindrical shape by being wound around the core 2 via the second bobbin 30. The wire of the second winding 40 is a Litz wire in which a plurality of enameled wires are twisted together. The diameter dimension of the wire of the second winding 40 is larger than the diameter dimension of the wire of the first winding 20. The second winding 40 overlaps the overlapping winding 21 of the first winding 20 in the radial direction. Since the non - overlapping winding 22 of the first winding 20 located adjacent to the overlapping winding 21 in the axial direction is not inserted into the second cylindrical portion 31, the second winding 40 does not overlap the non - overlapping winding 22 in the radial direction. The second winding 40 is positioned adjacent to the portion of the non - overlapping winding 22 of the first winding 20 that is radially outside the base layer 23 in the axial direction.

[0020] The cover component 3 is provided on the opposite side of the first bobbin 10 in the axial direction with the second bobbin 30 interposed therebetween. The cover component 3 has an end wall portion 26 and a cover portion 27. The end wall portion 26 is provided on the opposite side of the first bobbin 10 with the second cylindrical portion 31 of the second bobbin 30 interposed therebetween. The end wall portion 26 is formed in a plate shape with the axial direction as the thickness direction. The outer shape of the end wall portion 26 is the same as the outer shape of one end flange portion 12b when viewed from the axial direction. An insertion hole 26a penetrating the end wall portion 26 in the axial direction is formed in the end wall portion 26. The insertion hole 26a is formed in the same shape as the inner peripheral surface of the first cylindrical portion 11 when viewed from the axial direction. The cover portion 27 opens outward in the radial direction at a part of the outer edge of the end wall portion 26 in the circumferential direction. The opening of the cover portion 27 functions as an injection port 3a (see FIG. 1) of the cover component 3 into which a filling resin (not shown) for protecting the first winding 20 and the second winding 40 of the transformer 1 is injected.

[0021] The cover portion 27 has a first cover component 27a and a second cover component 27b arranged in the axial direction. The first cover component 27a extends axially from the outer edge of the end wall portion 26 to the outer edge of the second flange portion 32 of the second bobbin 30. Thereby, the first cover component 27a covers the overlapping portion 111 of the first cylindrical portion 11, the overlapping winding 21 of the first winding 20, the second cylindrical portion 31, and the outside of the second winding 40 in the radial direction. The second cover component 27b extends axially from the outer edge of the second flange portion 32 to the outer edge of one end flange portion 12b of the first bobbin 10. Thereby, the second cover component 27b covers the non-overlapping portion 112 of the first cylindrical portion 11 and the outside of the non-overlapping winding 22 of the first winding 20 in the radial direction.

[0022] As shown in FIGS. 1 and 2, the terminal blocks 8 are provided one by one on the end wall portion 26 of the cover component 3 and the one end flange portion 12b of the first bobbin 10. The terminal blocks 8 are provided at the ends of the end wall portion 26 and the one end flange portion 12b in the opening direction of the injection port 3a. The terminal block 8 includes a terminal block main body 8a and a pedestal 8b. Only the terminal block 8 on the end wall portion 26 side among the two terminal blocks 8 will be described, and the description of the terminal block 8 on the one end flange portion 12b side is omitted because it has the same configuration as the terminal block 8 on the end wall portion 26 side. The terminal block 8 is integrally formed with the end wall portion 26. The terminal block main body 8a projects axially outward from the end wall portion 26. The terminal block main body 8a extends in a direction orthogonal to the axial direction and the opening direction of the injection port 3a. The end face of the terminal block main body 8a on the side opposite to the opening direction of the injection port 3a is along the recess 53a. Thereby, the terminal block main body 8a is fitted into the recess 53a. The pedestal 8b is a rectangular plate-like member provided at both longitudinal ends of the terminal block main body 8a. The thickness direction of the pedestal 8b coincides with the opening direction of the injection port 3a. The pedestal 8b is placed on the end face of the connecting piece 53 on the side where the recess 53a opens. A nut placement portion 8c for arranging a hexagonal nut is formed on the pedestal 8b. The nut placement portion 8c is a recess formed in a hexagonal shape when viewed from the side opposite to the opening direction of the injection port 3a. Each pedestal 8b has a terminal 9 attached thereto.

[0023] The terminal 9 is formed of a metal material such as copper, for example. The terminal 9 has a terminal main body 9a and a support portion 9b. The terminal main body 9a is formed in a rectangular plate shape whose thickness direction coincides with the opening direction of the injection port 3a. The terminal main body 9a is placed on the pedestal 8b. The terminal main body 9a has a claw portion extending toward the pedestal 8b side, and is fixed to the pedestal 8b by a snap foot formed by the claw portion. A through hole 9c penetrating the terminal main body 9a in the thickness direction is provided in the terminal main body 9a. A hexagonal nut is arranged between the terminal main body 9a and the pedestal 8b. The hexagonal nut is non-rotatably arranged within the nut placement portion 8c of the pedestal 8b. A terminal (not shown) of an external power circuit is connected to the terminal main body 9a, for example, by bolt fastening. The support portion 9b is provided inside a pair of terminal main bodies 9a. The support portion 9b extends along the axial direction. The axially outer end of the support portion 9b is located axially outside the terminal main body 9a. The axially outer end of the support portion 9b is formed in a U shape that opens inward in the facing direction of the pair of terminal main bodies 9a when viewed from the axial direction. Inside the axially outer end of the support portion 9b, end portions 20a, 40a of the wire rods constituting the windings 20, 40 are arranged. The end portions 20a, 40a are fixed to the support portion 9b by, for example, welding in a state of being clamped to the axially outer end of the support portion 9b.

[0024] Next, the winding method of the first winding 20 in the above transformer 1 will be described. The following description of the winding method is made with reference to the schematic diagrams of FIGS. 3 to 8. Different winding methods are shown in FIGS. 4 to 8. In FIGS. 4 to 8, only the core 2 and the first winding 20 of the transformer 1 are shown. In FIGS. 4 to 8, as in FIG. 3, a pair of inner pieces 51 are integrated and simply illustrated as the core 2. The arrows shown in FIGS. 4 to 8 schematically indicate the advancing direction of the wire of the first winding 20. In the following description, as shown in FIG. 3, in the core 2, the portion corresponding to the end portion on the other end flange portion 12a side of the overlapping winding 21 of the first winding 20 in the axial direction is defined as the first portion 2a. In the core 2, the portion corresponding to the end portion on the center flange portion 12c side of the overlapping winding 21 in the axial direction is defined as the second portion 2b. In the core 2, the portion corresponding to the end portion on the center flange portion 12c side of the non-overlapping winding 22 of the first winding 20 in the axial direction is defined as the third portion 2c. In the core 2, the portion corresponding to the end portion on the one end flange portion 12b side of the non-overlapping winding 22 in the axial direction is defined as the fourth portion 2d.

[0025] In the first example of the winding method of the first winding 20 shown in FIG. 4, the first portion 2a of the core 2 is set as the winding start portion A of the wire. In the first example, first, the wire is extended axially along the outer peripheral surface of the core 2 from the first terminal 5a to the first portion 2a, and the wire is wound in one layer from the first portion 2a, which is the winding start portion A, to the fourth portion 2d. Thereby, a single layer of overlapping winding 21 is formed in the range from the first portion 2a to the second portion 2b, and a single layer of base layer 23 including the single layer of overlapping winding 21 is formed in the range from the first portion 2a to the fourth portion 2d. Subsequently, the wire is wound in a plurality of layers (two layers in FIG. 4) while reciprocating the wire in the range from the fourth portion 2d to the third portion 2c. Thereby, a plurality of layers (three layers in FIG. 4) of non-overlapping windings 22 including the base layer 23 are formed in the range from the third portion 2c to the fourth portion 2d. After the formation of the non-overlapping winding 22, the wire is extended from the fourth portion 2d to the second terminal 5b and the end portion of the wire is connected to the second terminal 5b, thereby completing the winding method of the first example.

[0026] In the second example of the winding method of the first winding 20 shown in FIG. 5, the second part 2b of the core 2 is taken as the winding start part A of the wire. In the second example, first, the wire is wound in one layer from the second part 2b, which is the winding start part A, to the first part 2a. Thereby, a single-layer overlapping winding 21 is formed in the range from the first part 2a to the second part 2b. Subsequently, the wire is extended from the first part 2a to the first terminal 5a, and one end of the wire is connected to the first terminal 5a. Also, the wire is wound in one layer from the second part 2b, which is the winding start part A, to the fourth part 2d. Thereby, a single-layer base layer 23 including the single-layer overlapping winding 21 is formed in the range from the first part 2a to the fourth part 2d. Subsequently, the wire is wound back and forth in a plurality of layers (two layers in FIG. 5) while reciprocating the wire in the range from the fourth part 2d to the third part 2c. Thereby, a plurality of layers (three layers in FIG. 5) of non-overlapping windings 22 including the base layer 23 are formed in the range from the third part 2c to the fourth part 2d. After the formation of the non-overlapping winding 22, the second example of the winding method is completed by extending the wire from the fourth part 2d to the second terminal 5b and connecting the other end of the wire to the second terminal 5b.

[0027] In the third example of the winding method of the first winding 20 shown in FIG. 6, the fourth part 2d of the core 2 is taken as the winding start part A of the wire. In the third example, first, the wire is extended from the second terminal 5b to the fourth part 2d, which is the winding start part A, and the wire is wound in one layer from the fourth part 2d to the first part 2a. Thereby, a single-layer overlapping winding 21 is formed in the range from the first part 2a to the second part 2b, and a single-layer base layer 23 including the single-layer overlapping winding 21 is formed in the range from the first part 2a to the fourth part 2d. Subsequently, the wire is extended axially without winding from the first part 2a to the third part 2c, and then the wire is wound back and forth in a plurality of layers (two layers in FIG. 6) while reciprocating the wire in the range from the third part 2c to the fourth part 2d. Thereby, a plurality of layers (three layers in FIG. 6) of non-overlapping windings 22 including the base layer 23 are formed in the range from the third part 2c to the fourth part 2d. After the formation of the non-overlapping winding 22, the third example of the winding method is completed by extending the wire from either the third part 2c or the fourth part 2d to the first terminal 5a and connecting the other end of the wire to the first terminal 5a.

[0028] In the fourth example of the winding method of the first winding 20 shown in FIG. 7, the fourth part 2d of the core 2 is set as the winding start part A of the wire. In the fourth example, first, the wire is extended from the second terminal 5b to the fourth part 2d which is the winding start part A, and the wire is wound in a plurality of layers (two layers in FIG. 7) while reciprocating the wire in the range from the fourth part 2d to the first part 2a. Thereby, a plurality of layers (two layers in FIG. 7) of overlapping windings 21 are formed in the range from the first part 2a to the second part 2b, and a plurality of layers (two layers in FIG. 7) of a base layer 23 including the plurality of layers of overlapping windings 21 are formed in the range from the first part 2a to the fourth part 2d. Subsequently, in the range from the fourth part 2d to the third part 2c, the wire is wound in one layer. Thereby, in the range from the third part 2c to the fourth part 2d, a plurality of layers (three layers in FIG. 7) of non-overlapping windings 22 that are one layer more than the overlapping windings 21 are formed. After the formation of the non-overlapping windings 22, the winding method of the fourth example is completed by extending the wire from either the third part 2c or the fourth part 2d to the first terminal 5a and connecting the other end of the wire to the first terminal 5a. In the fourth example, for example, after forming the plurality of layers of the base layer 23, in the range from the fourth part 2d to the third part 2c, the wire may be wound in a plurality of layers while reciprocating the wire.

[0029] In the fifth example of the winding method of the first winding 20 shown in FIG. 8, the fourth part 2d of the core 2 is used as the winding start part A of the wire. In the fifth example, first, the wire is extended from the second terminal 5b to the fourth part 2d which is the winding start part A, and the wire is wound one layer from the fourth part 2d to the third part 2c. Subsequently, the wire is extended axially without winding from the third part 2c to the first part 2a, and the wire is wound one layer from the first part 2a to the fourth part 2d. Thereby, a single-layer overlapping winding 21 is formed in the range from the first part 2a to the second part 2b, and a base layer 23 is formed in the range from the first part 2a to the fourth part 2d. The base layer 23 is a single layer composed of the overlapping winding 21 in the range from the first part 2a to the second part 2b, and two layers constituting the non-overlapping winding 22 in the range from the third part 2c to the fourth part 2d. Subsequently, in the range from the fourth part 2d to the third part 2c, the wire is wound a plurality of layers. Thereby, a plurality of layers (three layers in FIG. 8) of non-overlapping windings 22 having a larger number of layers than the overlapping winding 21 are formed in the range from the third part 2c to the fourth part 2d. After the formation of the non-overlapping winding 22, the winding method of the fifth example is completed by extending the wire from either the third part 2c or the fourth part 2d to the first terminal 5a and connecting the other end of the wire to the first terminal 5a. In the fifth example, for example, after forming the base layer 23, in the range from the fourth part 2d to the third part 2c, the wire may be wound a plurality of layers while reciprocating. The winding method of the first winding 20 is not limited to the above-described first to fifth examples.

[0030] In the transformer 1, the electrical coupling between the first winding 20 and the second winding 40 is dense in the overlapping winding 21 and sparse in the non-overlapping winding 22. Therefore, the leakage inductance generated between the first winding 20 and the second winding 40 is small in the overlapping winding 21 and large in the non-overlapping winding 22. For this reason, by adjusting the number of turns of the first winding 20 in the non-overlapping winding 22, the leakage inductance can be changed and adjusted to an appropriate value.

[0031] As described above, according to the transformer 1 according to the present embodiment, the first bobbin 10 is configured such that the first winding 20 can be wound around the non-overlapping portion 112 of the first cylindrical portion 11 rather than the overlapping portion 111 in the first cylindrical portion 11 so that the thickness in the radial direction of the first cylindrical portion 11 increases. Thereby, the manufacturer can change the thickness in the radial direction of the first winding 20 in the non-overlapping portion 112 without changing the thickness in the radial direction of the first winding 20 in the overlapping portion 111. For this reason, the manufacturer can adjust the leakage inductance without changing the thickness in the radial direction of the second winding 40 that overlaps the overlapping portion 111 in the radial direction. By changing the thickness in the radial direction of the first winding 20 in the non-overlapping portion 112, compared with the case of changing the thickness in the radial direction of the first winding 20 and the second winding 40 in the overlapping portion 111, the change in the radial volume of the first winding 20 and the second winding 40 can be suppressed to a small size. The first bobbin 10 has a central flange portion 12c that axially divides the first cylindrical portion 11 into an overlapping portion 111 that overlaps the second cylindrical portion 31 in the radial direction and a non-overlapping portion 112 that does not overlap the second cylindrical portion 31 in the radial direction in a state where the second bobbin 30 is assembled. Thereby, the manufacturer can axially divide the first winding 20 into an overlapping winding 21 that overlaps the second winding 40 in the radial direction and a non-overlapping winding 22 that does not overlap the second winding 40 in the radial direction only by assembling the first bobbin 10 and the second bobbin 30. Therefore, the manufacturer can easily form the overlapping winding 21 and the non-overlapping winding 22 as compared with the case where the first bobbin 10 is not provided with the central flange portion 12c. Thus, the manufacturer can easily adjust the thickness in the radial direction, the length in the axial direction, etc. of the first winding 20 in each of the overlapping portion 111 and the non-overlapping portion 112. Therefore, it is possible to provide a transformer 1 having excellent versatility in which the leakage inductance can be freely adjusted while suppressing a small change in volume.

[0032] In this embodiment, the second bobbin 30 is provided so as to be axially relatively movable with respect to the first bobbin 10. Thereby, the manufacturer can adjust the axial relative position between the first bobbin 10 and the second bobbin 30. For this reason, the manufacturer can adjust the position and the axial length of the overlapping portion between the first winding 20 and the second winding 40, and thus can freely adjust the leakage inductance.

[0033] In this embodiment, the second bobbin 30 is assembled on the radially outer side of the overlapping portion 111. Thereby, the manufacturer can change the radial thickness of the second winding 40 without changing the radial thickness of the first winding 20 in the overlapping portion 111. By changing the radial thickness of the second winding 40, compared with the case of changing the radial thicknesses of the first winding 20 and the second winding 40 in the overlapping portion 111, the change in the radial volume of the first winding 20 and the second winding 40 can be suppressed to be small. Further, the manufacturer can easily change the radial thickness and the axial length of the second winding 40 in a state where the second bobbin 30 is assembled to the first bobbin 10. Therefore, the manufacturer can easily adjust the leakage inductance by adjusting the radial thickness and the axial length of the second winding 40.

[0034] In this embodiment, after forming the base layer 23 in which the wire is wound around the overlapping portion 111 and the non-overlapping portion 112 at least one layer each, the first winding 20 is wound by overlapping the portion of the base layer 23 located in the non-overlapping portion 112. Thereby, in order to configure the first winding 20, compared with the case where the wire is wound a plurality of layers only in the non-overlapping portion 112 and then wound around the overlapping portion 111, it is possible to suppress the occurrence of variations in the relative axial position between the first winding 20 and the second winding 40. Also, it is possible to suppress or prevent the generation of stress in the first winding 20.

[0035] Specifically explaining the above points, if the wire of the first winding 20 is wound around the non-overlapping portion 112 in multiple layers and then wound around the overlapping portion 111, the wire will move radially inward from the non-overlapping portion 112 to the overlapping portion 111. For this reason, the second winding 40 interferes with the "portion of the wire moving radially inward" of the first winding 20. Furthermore, variations are likely to occur in the form of the "portion of the wire moving radially inward". For this reason, variations occur in the relative axial position between the first winding 20 and the second winding 40. Also, since the second winding 40 interferes with the "portion of the wire moving radially inward", stress is generated in the "portion of the wire moving radially inward".

[0036] On the other hand, when the first winding 20 is formed by winding the wire as illustrated in FIGS. 4 to 8, there is no "portion of the wire moving radially inward" from the non-overlapping portion 112 to the overlapping portion 111. Thereby, it is possible to suppress variations in the relative axial position between the first winding 20 and the second winding 40. Also, since the first winding 20 does not interfere with the second winding 40, it is possible to suppress or prevent stress from being applied to the wire of the first winding 20 by the second winding 40.

[0037] In the present embodiment, the radial separation distance between the second cylindrical portion 31 and the first cylindrical portion 11 is equal to or greater than twice the diameter dimension of the wire of the first winding 20. Thereby, the manufacturer can wind the first winding 20 around the space between the second cylindrical portion 31 and the first cylindrical portion 11 a plurality of times without changing the radial thickness of the second winding 40. Therefore, the manufacturer can adjust the leakage inductance while suppressing the change in the volume of the entire transformer 1 compared to the case of changing the radial thickness of the overlapping winding 21 in the first winding 20 and changing the radial thicknesses of the first winding 20 and the second winding 40.

[0038] As described above, the details of the present invention have been explained. However, the present invention is not limited to the above-described embodiments, and various changes can be made without departing from the gist of the present invention.

[0039] In the present invention, as shown in FIG. 9, the second winding 40 may be disposed radially inside the overlapping winding 21 of the first winding 20. FIG. 9 is a schematic diagram corresponding to FIG. 3. Hereinafter, the configuration of the transformer 1 shown in FIG. 9 will be specifically described. In the following description, the same reference numerals are given to the same components as those in the above-described embodiment, and the description thereof will be omitted.

[0040] The first cylindrical portion 11 has a small-diameter portion 15 and a large-diameter portion 16. The small-diameter portion 15 is formed in a cylindrical shape. The inner diameter dimension of the small-diameter portion 15 is larger than the outer diameter dimension of the core 2. At both axial ends of the small-diameter portion 15, one-end flange portion 12b and the central flange portion 12c of the first flange portion 12 are provided, projecting radially outward from the small-diameter portion 15. The large-diameter portion 16 is formed in a cylindrical shape coaxial with the small-diameter portion 15. The inner diameter dimension of the large-diameter portion 16 is larger than the inner diameter dimension of the small-diameter portion 15. The large-diameter portion 16 extends axially from the central flange portion 12c to the side opposite to the one-end flange portion 12b. At the end of the large-diameter portion 16 on the side opposite to the central flange portion 12c in the axial direction, the other-end flange portion 12a of the first flange portion 12 is provided, projecting radially outward from the large-diameter portion 16. The inner diameter dimensions of the other-end flange portion 12a and the central flange portion 12c are larger than the inner diameter dimension of the one-end flange portion 12b, and the outer diameter dimension of the other-end flange portion 12a is substantially the same as the outer diameter dimensions of the one-end flange portion 12b and the central flange portion 12c.

[0041] The inner diameter dimension of the second cylindrical portion 31 of the second bobbin 30 is substantially the same as the inner diameter dimension of the small-diameter portion 15 of the first bobbin 10, and the outer diameter dimension of the second flange portion 32 of the second bobbin 30 is smaller than the inner diameter dimension of the large-diameter portion 16 of the first bobbin 10. The second bobbin 30 is inserted inside the large-diameter portion 16. With the second bobbin 30 inserted into the large-diameter portion 16, the second bobbin 30 is adjacent in the axial direction to a portion of the small-diameter portion 15 of the first bobbin 10 that is located radially inward of the large-diameter portion 16. As a result, the second winding 40 wound around the second cylindrical portion 31 of the second bobbin 30 is disposed radially inward of the overlapping winding 21 of the first winding 20 wound around the large-diameter portion 16 of the first bobbin 10 and is axially adjacent to the non-overlapping winding 22 of the first winding 20 wound around the small-diameter portion 15. The core 2 is inserted inside the small-diameter portion 15 of the first bobbin 10 and inside the second bobbin 30 inserted into the large-diameter portion 16 of the first bobbin 10. The wire diameter dimension of the wire of the second winding 40 is substantially the same as the wire diameter dimension of the wire of the first winding 20. The radial separation distance between the second cylindrical portion 31 and the first cylindrical portion 11 is substantially the same as the wire diameter dimension of the wire of the first winding 20. For this reason, the second cylindrical portion 31 can wind the second winding 40 in one layer.

[0042] In this modified example, the second bobbin 30 is assembled radially inward of the overlapping portion 111. As a result, the manufacturer can change the radial thickness of the first winding 20 at the overlapping portion 111 without changing the radial thickness of the second winding 40. By changing the radial thickness of the first winding 20 at the overlapping portion 111, the change in the radial volume of the first winding 20 and the second winding 40 can be suppressed to be smaller compared to the case of changing the radial thickness of the first winding 20 and the second winding 40 at the overlapping portion 111. Also, with the second bobbin 30 assembled to the first bobbin 10, the manufacturer can easily change the radial thickness and the axial length of the first winding 20 at the overlapping portion 111. Therefore, the manufacturer can easily adjust the leakage inductance by adjusting the radial thickness and the axial length of the first winding 20 at the overlapping portion 111.

[0043] In the present invention, the second bobbin 30 is not limited to a resin-molded part. The second bobbin 30 may be, for example, an insulating tape wound around the outer peripheral surface of the first winding 20.

[0044] In the present invention, the shape of the core 2 is not limited to a cylindrical shape. The core 2 may be formed, for example, in a prismatic shape.

[0045] In the present invention, the first winding 20 may be used as the secondary winding and the second winding 40 may be used as the primary winding.

Explanation of Reference Numerals

[0046] 1 Transformer 2 Core 10 First bobbin 11 First cylindrical part 111 Overlapping part 112 Non-overlapping part 12c Central flange part (wall part) 20 First winding 30 Second bobbin 31 Second cylindrical part 40 Second winding

Claims

1. a first bobbin having a first cylindrical portion; a first winding wound around the first cylindrical portion; a second bobbin having a second cylindrical portion, the second bobbin being assembled to the first bobbin such that the second cylindrical portion overlaps the first cylindrical portion in a radial direction of the first cylindrical portion; a second winding wound around the second cylindrical portion; a core inserted through the first and second cylindrical portions, and comprising: in a state where the second bobbin is assembled, the first bobbin has a wall portion that axially divides the first cylindrical portion into an overlapping portion that overlaps the second cylindrical portion in a radial direction and a non-overlapping portion that does not overlap the second cylindrical portion in the radial direction; the first bobbin is configured such that the first winding can be wound around the non-overlapping portion of the first cylindrical portion rather than the overlapping portion of the first cylindrical portion so that a thickness of the first cylindrical portion in a radial direction becomes larger; the second bobbin is assembled to be relatively movable in an axial direction of the first cylindrical portion with respect to the first bobbin, and is assembled inside a radial direction of the overlapping portion of the first cylindrical portion, a transformer.

2. The transformer according to claim 1, wherein the second bobbin is assembled outside a radial direction of the overlapping portion of the first cylindrical portion.

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