Low-profile transformer and method for manufacturing the same

Abstract

Provided are: a low-profile transformer which is equipped with a plurality of cylindrical secondary coils and is capable of being more compact and having a lower product height in comparison to the prior art; and a method for producing the same.　Thus, a transformer equipped with a primary coil 34 which is wound around the outer circumference of the center legs 4c, 6c of first and second cores 4, 6 which constitute a magnetic core, and also equipped on the outer circumference thereof with cylindrical secondary coils 22, 24 which are concentrically arranged relative to one another and also relative to the primary coil 34, wherein: the cylindrical secondary coils 22, 24 are provided with cylindrical secondary coil main body sections 22d, 24d which encircle and sandwich slits 22c, 24c therebetween, and terminal units 22a, b, 24a, b which each extend toward the outside from a region near the end section of the cylindrical secondary coil main body sections, which face one another with the slits 22c, 24c sandwiched therebetween; and the cylindrical secondary coils 22, 24 are positioned in a manner such that there is overlap between one of the terminal units 22a, 24a in each of said coils, and there is no contact between the other of the terminal units 22b, 24b in each of said coils.

Description

Technical Field

[0001] The present invention relates to a low-profile transformer and a method for manufacturing the same, and particularly to a low-profile transformer for power conversion, in which a primary coil and a secondary coil are arranged concentrically, and a method for manufacturing the same, which are used in a step-down DC-DC converter or the like of an electric vehicle or a hybrid vehicle (EV / HEV vehicle).

Background Art

[0002] For the transformer for power conversion of a switching power supply, specifications of an output voltage of about 12V and an output current of about 100A are required due to the demand for a step-down DC-DC converter or the like of recent EV / HEV vehicles. In addition, miniaturization and weight reduction of an in-vehicle converter unit are required, and particularly, it is an urgent task to promote miniaturization and weight reduction of a main transformer which is a large-sized component. As a conventional technique for miniaturizing a transformer with a large current specification, there is known a transformer 120 disclosed in Patent Document 1 below (particularly FIG. 1) described with reference to FIG. 7 of the present application, in which a primary coil 134 and a secondary coil 136 made of a cylindrical copper plate are housed between two PQ cores 146 and 148.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, in such power conversion transformers, it is necessary to use multiple secondary coils in order to obtain a larger current. In the case of the above-mentioned reference 1, multiple secondary coils 136, 136 are stacked outside the primary coil 134 in the winding axis direction, concentrically with the primary coil 134, and outputs are obtained from each of the terminals 136a, 136a of each stacked secondary coil 136, 136. However, in the case of this cited reference 1, the product height increased in proportion to the number of stacked secondary coils 136, 136, making it difficult to promote the reduction in height and miniaturization of the product.

[0005] This invention has been made in view of these circumstances, and aims to provide a low-profile transformer and a method for manufacturing the same that can promote the reduction in profile and miniaturization of a product when multiple secondary coils are arranged outside the primary coil. [Means for solving the problem]

[0006] The low-profile transformer of the present invention is A magnetic core and A primary coil is arranged in a wound state around the outer circumference of the magnetic core of the magnetic material core, On the outer circumference of the primary coil, concentrically with the primary coil, and relative to each other Overlapping in the radial direction It comprises at least two cylindrical secondary coils arranged concentrically, Each of the at least two cylindrical secondary coils has a cylindrical shape that encircles the slit. Made of a specified conductive material A cylindrical secondary coil body is provided, and terminal portions are provided on one longitudinal end of the slit of the cylindrical secondary coil body, extending outward from each of the regions near the ends of the cylindrical secondary coil body that are opposite each other across the slit. In each of the at least two cylindrical secondary coils, one terminal portion is arranged to overlap and be electrically connected to the other, while the other terminal portion is arranged to be in a non-contact state with the other. the law of nature, The cross-sectional area of ​​the at least two cylindrical secondary coils is adjusted so that the output current value is equivalent, according to the coil diameter of each cylindrical secondary coil. It is characterized by the following: Here, the term "end portion of the cylindrical secondary coil body" refers to the regions of the cylindrical secondary coil body that are opposite each other across the slit. Furthermore, it is preferable that all of the at least two cylindrical secondary coils are made by processing a plate-shaped conductive material made of the same material into a cylindrical shape. In this case, it is preferable that the same material is copper or aluminum.

[0007] Furthermore, in each of the at least two cylindrical secondary coils, the cylindrical secondary coil body portion is formed The aforementioned predetermined conductive material Preferably, the terminal portion of the cylindrical secondary coil is formed by a plate material, and a notch is provided in the corner formed by the side surface of each terminal portion in the extending direction that is opposite to the terminal portion from the slit, and the edge surface of the cylindrical secondary coil body. Furthermore, it is preferable that in each of the at least two cylindrical secondary coils, one terminal portion and the other terminal portion are formed to be substantially parallel to each other and to extend outward while bending.

[0008] Furthermore, in each of the at least two cylindrical secondary coils, it is preferable that the cross-section of the cylindrical secondary coil body is rectangular, with the longer side of the rectangle forming the circumferential surface of the cylinder and the shorter side of the rectangle forming the radial surface of the cylinder. Furthermore, it is preferable that the primary coil is an air-core coil in which the conductor is wound multiple times.

[0009] The method for manufacturing a low-profile transformer according to the present invention is: The first step involves arranging a primary coil in a wound state around the outer circumference of the middle leg portion of one of the first and second cores that constitute the magnetic core, For each of at least two cylindrical secondary coils, a cylindrical secondary coil body is formed from a predetermined metal material, encircling the slit, and one terminal portion is extended in a predetermined direction from each of the regions near the ends of the cylindrical secondary coil body opposite each other on one end of the slit in the longitudinal direction. Furthermore, when forming the cylindrical secondary coil body, the cross-sectional area is adjusted according to the coil diameter of each cylindrical secondary coil so that the output current value is equivalent. The second step, On the outer circumference of the primary coil, concentrically and relative to the primary coil, Overlapping in the radial directionA third step involves arranging the at least two cylindrical secondary coils concentrically, A fourth step involves arranging each of the at least two cylindrical secondary coils such that one of the two terminal portions is electrically connected to the other by overlapping them, while the other terminal portion is not in contact with the other; A fifth step involves combining the first and second cores to form the magnetic core by abutting the other middle leg of the first middle leg, which is located at the center of the primary coil and the at least two cylindrical secondary coils that are arranged concentrically, and housing the primary coil and the at least two cylindrical secondary coils within this magnetic core. The manufacturing process is characterized by carrying out the process in such an order that the third and fourth steps occur after the second step, and the fifth step occurs after the first, second, third, and fourth steps.

[0010] Furthermore, the second step includes a manufacturing step of forming the cylindrical secondary coil body by sheet metal processing of a sheet material made of the predetermined metal material, and extending one terminal portion in a predetermined direction from each of the regions near the ends of the cylindrical secondary coil body, When extending the terminal portion in the predetermined direction, it is preferable to provide a notch in the corner formed by the side of each terminal portion located on the side opposite to the slit in the extending direction and the edge of the cylindrical secondary coil body, so that the extending direction of the terminal portion can be adjusted. [Effects of the Invention]

[0011] According to the low-profile transformer and its manufacturing method of the present invention, by arranging a plurality of cylindrical secondary coils concentrically on the same plane, the height dimension can be significantly reduced compared to conventional transformers in which a plurality of secondary coils are stacked in the winding axis direction, thereby promoting the reduction in profile and miniaturization of the product. [Brief explanation of the drawing]

[0012] [Figure 1] These are perspective views (A) seen from obliquely above the front and (B) seen from obliquely above the back, showing the structure of a low-profile transformer according to an embodiment of the present invention. [Figure 2] This is an exploded perspective view showing the structure of a low-profile transformer according to an embodiment of the present invention. [Figure 3] This is a perspective view showing an enlarged cylindrical secondary coil of a low-profile transformer according to an embodiment of the present invention. [Figure 4] These are schematic views showing two cylindrical secondary coils according to an embodiment of the present invention ((a) is the overlapping state of the terminal portions of the two cylindrical secondary coils, (b) is the shape of the first cylindrical secondary coil, and (c) is the shape of the second cylindrical secondary coil). [Figure 5] This is a diagram for explaining a cylindrical secondary coil manufactured using sheet metal processing techniques. (A) is a perspective view seen from obliquely below the bottom surface, and (B) is a developed view showing the shape of the sheet-like conductive material before sheet metal processing. [Figure 6] These are schematic views for explaining the difference in height dimensions in the assembled states of Comparative Example (A) and Example (B) ((a) is a front view of the transformer, and (b) is a perspective view showing the shape of the cylindrical secondary coil). [Figure 7] This is a perspective view of a transformer according to the prior art seen from obliquely above the front.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, a low-profile transformer according to an embodiment of the present invention and a method for manufacturing the low-profile transformer will be described with reference to the drawings. The low-profile transformer of this embodiment is applied to, for example, an in-vehicle power conversion transformer. FIG. 1(A) is a perspective view of a low-profile transformer according to an embodiment of the present invention seen from obliquely above the front side, and FIG. 1(B) is a perspective view of a low-profile transformer according to an embodiment of the present invention seen from obliquely above the back side. Also, FIG. 2 is an exploded perspective view showing the low-profile transformer according to an embodiment of the present invention.

[0014] (Low-profile transformer) As shown in Figures 1(A), (B) and 2, the low-profile transformer 10 of this embodiment comprises, as its main elements, a first core 4 and a second core 6 made of PQ cores that constitute a magnetic core, a primary coil (preferably an air-core coil) 34 made by winding a wire, and first and second cylindrical secondary coils 22 and 24 made of cylindrical metal plates. The first core 4 and the second core 6 are made of, for example, ferrite core, and each has cylindrical middle legs 4c and 6c, outer legs 4a, 4b, 6a, and 6b arranged on both sides of the middle legs 4c and 6c, and back parts 4d and 6d connecting the middle legs 4c and 6c and the outer legs 4a, 4b, 6a, and 6b. The first core 4 and the second core 6 are symmetrical in shape, and the two cores 4 and 6 are combined such that corresponding members are positioned opposite each other.

[0015] Furthermore, the outer leg portions 4a, 4b, 6a, and 6b have a plate shape with an arc-shaped inner surface and a flat outer surface. Furthermore, the corresponding tips of the three legs 4a, 4b, and 4c constituting the first core 4 and the three legs 6a, 6b, and 6c constituting the second core 6 are preferably arranged to face each other with a small gap (not shown) in between.

[0016] The transformer structure is preferably a closed magnetic circuit, and instead of a PQ core, an EE core, EI core, or ER core can be used. Of course, it is also possible to adopt an open magnetic circuit structure using an I core or the like. Furthermore, a primary coil 34 of an air-core coil, formed by winding a wire, is arranged around the outer circumference of the middle legs (magnetic cores) 4c and 6c of the first core 4 and second core 6 that constitute the PQ core, as described above. Alternatively, instead of forming the primary coil 34 as an air-core coil, an insulating resin bobbin may be placed around the outer circumference of the middle legs (magnetic core) 4c and 6c, and a conductor may be wound around this resin bobbin. Of course, even when using the primary coil 34 of the air-core coil described above, resin bobbins may be placed around the middle legs (magnetic cores) 4c and 6c.

[0017] The inner diameter of the second cylindrical secondary coil 24 is formed to be larger than the outer diameter of the first cylindrical secondary coil 22, and is sized so that the first cylindrical secondary coil 22 fits inside the second cylindrical secondary coil 24 with a small gap between them. In other words, the primary coil 34, the first cylindrical secondary coil 22, and the second cylindrical secondary coil 24 are arranged concentrically in this order, centered on the central axes of the middle legs (magnetic cores) 4c and 6c of the first core 4 and the second core 6 that constitute the PQ core. Although not shown in the diagram, in reality, bobbins made of insulating material such as phenolic resin, or separators made of insulating material molded to correspond to the shapes of the cylindrical secondary coils 22 and 24, are interposed between each of the coils 34, 22, and 24.

[0018] The first cylindrical secondary coil 22 and the second cylindrical secondary coil 24 are made by processing a plate-shaped conductive material such as copper or aluminum into a cylindrical shape. These cylindrical secondary coils 22 and 24 have cylindrical secondary coil body portions 22d and 24d formed by sandwiching a plate-shaped conductive material around slits 22c and 24c, and terminal portions 22a, 22b, 24a, and 24b are located at the longitudinal lower ends of the circumferential ends of the coils facing each other across the slits 22c and 24c, respectively, extending from the vicinity of the ends of the cylindrical secondary coil body portions 22d and 24d facing each other across the slits 22c and 24c. Although the terminals 34a and 34b of the primary coil 34 are arranged to extend upward from the primary coil 34 as shown in Figures 1(A) and (B), the direction in which the terminals 34a and 34b are extended is not limited to this.

[0019] Furthermore, the terminal portions 22a and 22b of the first cylindrical secondary coil 22, and the terminal portions 24a and 24b of the second cylindrical secondary coil 24 are all configured to extend substantially parallel to each other. In addition, these terminal portions 22a, 22b, 24a, and 24b are formed to extend outward while bending. Specifically, the terminal portions 22a, 22b, 24a, and 24b extend forward from the cylindrical secondary coil body portions 22d and 24d, then bend downward, and then bend forward again. The forward-extending tips of the terminal portions 22a, 22b, 24a, and 24b are configured such that their bottom surfaces are electrically connected, for example, to a conductive pattern on a substrate by soldering.

[0020] One terminal portion 24a of the second cylindrical secondary coil 24 is superimposed on one terminal portion 22a of the first cylindrical secondary coil 22, so that these two terminal portions 22a and 24a are electrically connected (at a common potential) (see Figures 4(a), (b), and (c)). In contrast, the other terminal portion 24b of the second cylindrical secondary coil 24 is positioned so as not to overlap with the other terminal portion 22b of the first cylindrical secondary coil 22, and the two terminal portions 22b and 24b are spaced apart from each other (see Figures 4(a), (b), and (c)). Therefore, while the tips of both terminal portions 22a and 22b of the first cylindrical secondary coil 22 are designed to be placed on the same plane (substrate surface), the terminal portions 24a and 24b of the second cylindrical secondary coil 24 are configured such that the tip of terminal portion 24a is positioned above the tip of terminal portion 24b by the thickness of terminal portion 22a. This is because the tip of terminal portion 24a is superimposed on the tip of terminal portion 22a of the first cylindrical secondary coil 22, while the tip of terminal portion 24b needs to be configured to be placed on the substrate surface in the same way as the terminal portions 22a and 22b of the first cylindrical secondary coil 22.

[0021] Furthermore, if there is a request to reduce the width of the slits 22c and 24c of each cylindrical secondary coil 22 and 24, the overlapping terminal portions 22a and 24a will be placed between the other terminal portions 22b and 24b (see Figure 4(a)). However, if there is no restriction on the width of the slits 22c and 24c, the overlapping terminal portions 22a and 24a do not need to be placed between the other terminal portions 22b and 24b. In particular, when three or more cylindrical secondary coils are stacked concentrically, it is necessary to adjust the position of one of the terminal sections being stacked and the width of the slits so that the other terminal sections can be positioned at predetermined locations spaced apart from each other.

[0022] However, the terminal portions 22a, 22b, 24a, and 24b do not necessarily have to be configured to extend outward while bending as in the above embodiment, in whole or in part, but may be configured to extend in a straight line. Furthermore, for example, when connecting to a conductive pattern on the back side by penetrating through holes in the substrate, it is important to configure the downward-extending portions of the terminal portions 22a, 22b, 24a, and 24b to be longer.

[0023] Furthermore, the two cylindrical secondary coils 22 and 24 have rectangular cross-sections for their cylindrical secondary coil bodies 22d and 24d. The longer sides of this rectangle form the circumferential surface of the cylinder, and the shorter sides form the radial surface of the cylinder. This allows for a thinner radial thickness, making it easier to arrange the two cylindrical secondary coils 22 and 24 concentrically. Furthermore, since the two cylindrical secondary coils 22 and 24 have different coil diameters, their total coil lengths will differ, and under normal circumstances, the output current values ​​will be different. If it is necessary to make the output current values ​​between them equal (or in some other predetermined ratio), it is essential to adjust the cross-sectional area of ​​each coil 22 and 24 according to their respective coil diameters.

[0024] Incidentally, the cylindrical secondary coils 22 and 24 of the low-profile transformer 10 according to the above embodiment can be manufactured by various methods such as mold forming and sheet metal processing, but sheet metal processing is preferred because it is simpler. In this sheet metal processing method, for example, as shown in Figure 5(A), which is a view of the cylindrical secondary coil 24 from the bottom at an oblique angle, notches 24e and f are provided in the edge portions (corners) of the cylindrical secondary coil body 24d from which the terminal portions 24a and 24b branch off. By providing these notches 24e and f, when forming the cylindrical secondary coil body 24d into a cylindrical shape, the two terminal portions 24a and 24b can extend forward in a parallel shape to each other, rather than becoming a V-shape that widens towards the end.

[0025] Figure 5(B) is an unfolded view showing the shape of the sheet conductive material before sheet metal processing to form the cylindrical secondary coil 24. As shown in this unfolded view, notches 24e and f, which are cut out to become narrower on the inside, are provided at the edges (corners) of the cylindrical secondary coil body 24d, where the terminal portions 24a and 24b branch off, before sheet metal processing. The edges of the notches 24e and f on the cylindrical secondary coil body 24d side are given a radius of R (=2.0). An example of other dimensions of the cylindrical secondary coil 24 is also shown in Figure 5(B).

[0026] (Manufacturing method for low-profile transformers) The manufacturing method of the low-profile transformer according to this embodiment will be briefly described below using an example. First, a first step is performed in which a primary coil 34 of an air-core coil is formed by winding a wire around the outer circumference of the middle leg portion (magnetic core) 4c of the first core 4, which is made up of a PQ core that constitutes the magnetic material core. In addition, as mentioned above, the first step may be performed by placing an insulating resin bobbin around the outer circumference of the middle leg portion (magnetic core) 4c and forming the primary coil 34 by winding a wire around this resin bobbin.

[0027] Next, a second step is performed to create the two cylindrical secondary coils 22 and 24. The second step is performed by forming cylindrical secondary coil body portions 22d and 24d that encircle the slits 22c and 24c using a metal material such as copper or aluminum, and by making one bent terminal portion 22a, b, 24a, and b protrude from each of the cylindrical secondary coil body portion 22d and 24d regions that face each other across the slits 22c and 24c on one longitudinal end of the slits 22c and 24c. Note that this second step can also be performed before the first step.

[0028] Next, a third step is performed in which the two cylindrical secondary coils 22 and 32, formed as described above, are respectively placed on the outer circumference of the primary coil 34, concentrically with the primary coil 34. That is, the primary coil 34, the first cylindrical secondary coil 22, and the second cylindrical secondary coil 24 are arranged concentrically from the inside out, with the central legs (magnetic cores) 4c and 6c as the center.

[0029] Next, a fourth step is performed in which, of the two terminal portions 22a, 24a, one of the two terminal portions 22a, b, 24a, b of each of the two cylindrical secondary coils 22, 24 is electrically connected by overlapping them, while the other terminal portions 22b, 24b are arranged so that they are not in contact with each other.

[0030] Finally, a fifth step is performed to combine the first core 4 and the second core 6, such that the middle leg portion 6c and outer leg portions 6a, 6b of the second core 6, which is made up of a PQ core that constitutes the magnetic core, face the middle leg portion 6c and outer leg portions 6a, 6b of the first core 4 with a gap in between. This allows the primary coil 34 and the two cylindrical secondary coils 22, 24 to be housed concentrically between the first core 4 and the second core 6. Although the third and fourth steps described above are performed after the second step, the first step can also be performed between the second and third steps, or after the third step.

[0031] (Examples) The following examples will be compared with comparative examples to specifically demonstrate how the low-profile transformer according to this embodiment can promote a lower profile (see Figure 6).

[0032] (A) Structure of the comparative example As shown in Figure 6(A)(a), the transformer in the comparative example has a primary coil 234 sandwiched between two secondary coils 222 and 224, as shown in (A)(b), arranged so that they are superimposed in the axial direction. The secondary coils 222 and 224 in this comparative example are formed by wrapping a flat copper wire around a ring, with an annular portion and two bent terminal portions extending from this annular portion. The cross-section of the annular portion is shorter in the axial direction. Specifically, this flat wire has, for example, a long side of 6 mm and a short side of 3.3 mm (cross-sectional area of ​​19.8 mm²). 2 In the annular portion, the longer sides are oriented radially and the shorter sides oriented axially. The transformer in this comparative example, arranged in this manner, is formed with a width of 50 mm and a height of 36 mm, as shown in the front view (A)(a).

[0033] (B) Configuration of the embodiment On the other hand, as shown in Figure 6(B)(a), the low-profile transformer according to the embodiment has two cylindrical secondary coils 22 and 24, shown in (B)(b), arranged concentrically around the outer circumference of a primary coil (not shown). The cylindrical secondary coils 22 and 24 in this comparative example are formed by circling a flat copper wire, and are similar to the comparative example in that they have a cylindrical portion and two bent terminal portions extending from this cylindrical portion, but the cross-section of the cylindrical portion is shorter in the radial direction. Specifically, this flat wire has, for example, a long side of 10 mm and a short side of 2.0 mm (cross-sectional area of ​​20.0 mm²). 2 In the cylindrical portion, the longer side is oriented axially and the shorter side is oriented radially. As shown in the front view (B)(a), the low-profile transformer in this configuration has a width of 50 mm, the same as the comparative example above, but a height of 28.4 mm. As described above, the low-profile transformer of this embodiment is significantly lower in height compared to the conventional comparative example, with a reduction of 7.6 mm and a reduction of 21%.

[0034] (Type of change) Furthermore, the low-profile transformer and the method for manufacturing the low-profile transformer of the present invention are not limited to those of the embodiments described above, and various other embodiments can be applied. For example, in the above embodiment, two cylindrical secondary coils are arranged concentrically, but three or more cylindrical secondary coils may be arranged concentrically.

[0035] Furthermore, in the above embodiment, the terminal portion of the cylindrical secondary coil is formed to extend outward while bending, but the terminal portion may be made to extend linearly (for example, downward) without bending. Furthermore, regarding the core, as mentioned above, it is not limited to the type in which two PQ cores are combined to form a closed magnetic circuit, but may also be a type in which two E cores, ER cores, or other cores are combined to form a closed magnetic circuit. In addition, a type in which an open magnetic circuit is formed by an I core, etc., can also be used.

[0036] Furthermore, in the above embodiment, the two terminal portions of the cylindrical secondary coil are arranged to be approximately parallel to each other, thereby enabling a compact arrangement of the terminal portions. However, if there is sufficient space for arranging the terminal portions, they do not necessarily have to be parallel to each other. Furthermore, in the above embodiment, a notch is provided in the corner formed by the side of the terminal portion located on the side opposite to the slit in the extending direction and the circumferential surface of the cylindrical secondary coil body. However, if the cylindrical secondary coil is formed by a method such as mold molding rather than sheet metal processing, or if the terminal portion is connected to the cylindrical secondary coil body by welding or the like, the above notch does not need to be provided.

[0037] Furthermore, in the manufacturing method for low-profile transformers according to this embodiment, the manufacturing is carried out in the order described above from the first to the fifth step. However, as long as the manufacturing is carried out in an order such that the third and fourth steps come after the second step, and the fifth step comes after the first, second, third, and fourth steps, the other steps can be carried out in an order appropriate to the circumstances. For example, the second step may be performed before the first step, or the second and fourth steps may be performed in this order, followed by the first and third steps in this order. [Explanation of Symbols]

[0038] 4. First Core 4a, 4b, 6a, 6b outer legs 4c, 6c middle leg 4d, 6d back part 6. Second Core 10 Low-profile transformers 22 First cylindrical secondary coil 22a, 22b, 24a, 24b, 34a, 34b, 136a Terminal section 22c, 24c slit 22d, 24d Cylindrical secondary coil body 24. Second cylindrical secondary coil 24e, 24f notches 120 transformers 146, 148 PQ cores 34, 134, 234 Primary coil 222, 136, 224 Secondary coil

Claims

1. A magnetic core and A primary coil is arranged in a wound state around the outer circumference of the magnetic core of the magnetic material core, The primary coil is provided with at least two cylindrical secondary coils arranged on its outer circumference in a concentric manner with respect to the primary coil, and overlapping each other radially. Each of the at least two cylindrical secondary coils is provided with a cylindrical secondary coil body made of a predetermined conductive material that forms a cylindrical shape encircling a slit, and terminal portions extending outward from each of the regions near the ends of the cylindrical secondary coil body that are opposite each other across the slit, at one longitudinal end of the cylindrical secondary coil body. In each of the at least two cylindrical secondary coils, one terminal portion is arranged to overlap and be electrically connected to the other, while the other terminal portion is arranged to be in a non-contact state with the other. A low-profile transformer characterized in that the cross-sectional area of ​​at least two cylindrical secondary coils is adjusted so that the output current value is equivalent according to the coil diameter of each cylindrical secondary coil.

2. The low-profile transformer according to Claim 1, characterized in that all of the at least two cylindrical secondary coils are made by processing a plate-shaped conductive material of the same material into a cylindrical shape.

3. The low-profile transformer according to claim 2, characterized in that the same material is copper or aluminum.

4. The low-profile transformer according to claim 1, characterized in that in each of the at least two cylindrical secondary coils, the terminal portion of the cylindrical secondary coil is formed by a plate made of the predetermined conductive material that constitutes the cylindrical secondary coil body, and a notch is provided in the corner formed by the side surface in the extending direction of each terminal portion that is located on the side opposite to the terminal portion from the slit and the edge surface of the cylindrical secondary coil body.

5. The low-profile transformer according to claim 1, characterized in that in each of the at least two cylindrical secondary coils, one terminal portion and the other terminal portion are formed to be substantially parallel to each other and to extend outward while bending.

6. The low-profile transformer according to claim 1, characterized in that in each of the at least two cylindrical secondary coils, the cross-section of the cylindrical secondary coil body is rectangular, the longer side of the rectangle forms the circumferential surface of the cylinder, and the shorter side of the rectangle forms the radial surface of the cylinder.

7. The low-profile transformer according to claim 1, characterized in that the primary coil is an air-core coil in which a conductor is wound multiple times.

8. The first step involves arranging a primary coil in a wound state around the outer circumference of the middle leg portion of one of the first and second cores that constitute the magnetic core, A second step involves forming a cylindrical secondary coil body portion around a slit using a predetermined metal material for each of at least two cylindrical secondary coils, extending one terminal portion in a predetermined direction from each of the regions near the ends of the cylindrical secondary coil body portions facing each other on one end of the slit in the longitudinal direction, and further adjusting the cross-sectional area when forming the cylindrical secondary coil body portion so that the output current values ​​are equivalent according to the coil diameter of each cylindrical secondary coil. A third step involves arranging at least two cylindrical secondary coils on the outer circumference of the primary coil, concentrically with the primary coil and overlapping each other radially. A fourth step involves arranging each of the at least two cylindrical secondary coils such that, of the two terminal portions, one terminal portion is superimposed on the other and electrically connected, while the other terminal portion is not in contact with the other; A fifth step involves combining the first core and the second core to form the magnetic core by abutting the other middle leg portion of the central portion of one of the central portions of the primary coil and the at least two cylindrical secondary coils, which are arranged concentrically, and housing the primary coil and the at least two cylindrical secondary coils within this magnetic core. A method for manufacturing a low-profile transformer, characterized in that the manufacturing process is carried out in such an order that the third and fourth steps occur after the second step, and the fifth step occurs after the first, second, third, and fourth steps.

9. The second step includes a manufacturing step of forming the cylindrical secondary coil body by sheet metal processing of a sheet material made of the predetermined metal material, and extending one terminal portion in a predetermined direction from each of the regions near the ends of the cylindrical secondary coil body, The method for manufacturing a low-profile transformer according to claim 8, characterized in that, when extending the terminal portion in the predetermined direction, a notch is provided in the corner formed by the side of each terminal portion located on the side opposite to the slit and the edge of the cylindrical secondary coil body, so that the direction of extension of the terminal portion can be adjusted.

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