JP2009252845A - Balloon transformer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a balloon transformer which uses a drum type core and whose primary winding and secondary winding are different in number of turns. <P>SOLUTION: The balloon transformer includes the drum type core 110 having a core portion 111 and a pair of collar portions 112 and 113, terminal electrodes 141 to 144 provided to the collar portions 112 and 113, and windings 131 and 132 wound around the core portion 111. The number of turns of the winding 131 is larger than that of the winding 132, and the winding 131 has a parallel winding portion 131x wound in parallel along the winding 132 and a cross winding portion 131y wound crossing the winding 132, the parallel winding portion 131x being longer than the cross winding portion 131y. A decrease in magnetic balance caused when the windings 131 and 132 are unevenly wound is suppressed while a decrease in magnetic coupling caused by the cross winding portion 131x is suppressed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a balun transformer, and more particularly to a balun transformer using a drum core.

  Usually, a transmission line connected to an antenna or the like is an unbalanced transmission line, while a transmission line connected to a high-frequency circuit such as a semiconductor IC is a balanced transmission line. For this reason, when connecting an unbalanced transmission line and a balanced transmission line, the balun transformer which mutually converts an unbalanced signal and a balanced transmission line is inserted between them. Here, the unbalanced signal refers to a single-ended signal based on a fixed potential (for example, ground potential), and the balanced signal refers to a differential signal.

  As the balun transformer, a type using a glasses-type core as described in Patent Document 1 and a type using a toroidal core as described in Patent Document 2 are common. However, the balun transformer using the glasses-type core and the toroidal core has a problem that it is relatively large in overall size, and it is difficult to automate the winding operation and surface mount.

On the other hand, the balun transformer using the drum core described in Patent Document 3 has the advantage that it is easy to downsize, and is suitable for automation of winding work and surface mounting. Yes.
Japanese Patent Laid-Open No. 11-135330 JP-A-8-115820 JP 2005-39446 A

  However, there are types of balun transformers in which the number of turns of the primary winding and the secondary winding is different. When a drum-type core is used in such a type of balun transformer, there is a problem that the characteristics greatly change depending on the winding method.

  In other words, when the number of turns of the primary winding and the secondary winding is different, if the winding is performed by a normal method, that is, a method in which the amount of movement in the axial direction of the winding accompanying the winding is constant, the primary winding The winding and the secondary winding are wound non-parallel. As a result, the magnetic coupling is lowered as compared with the case where the primary winding and the secondary winding are wound in parallel, and there arises a problem that the insertion loss increases particularly in a high frequency region. On the other hand, when the primary winding and the secondary winding are wound in parallel, due to the difference in the number of turns, the winding with the smaller number of turns (for example, the primary winding) is turned into the winding with the larger number of turns (for example, the primary winding). The secondary winding) is wound together. In this case, the magnetic balance is remarkably lowered by uneven winding, and various characteristics are greatly deteriorated.

  Accordingly, an object of the present invention is to improve the characteristics of a balun transformer using a drum-type core, in which the number of turns of the primary winding and the secondary winding is different.

  A balun transformer according to the present invention is wound around a core portion and a drum core having a pair of flange portions provided at both ends of the core portion, a plurality of terminal electrodes provided at the flange portion, and the core portion. The first and second windings having both ends connected to the terminal electrode, the number of turns of the second winding is greater than the number of turns of the first winding, It has a parallel winding part wound in parallel along the second winding, and a cross winding part wound so as to cross the second winding, and the parallel winding part is It is characterized by being longer than the cross winding part.

  According to the present invention, since the parallel winding portion is set longer than the cross winding portion, the first and second windings are suppressed while suppressing a decrease in magnetic coupling occurring in the cross winding portion. It is possible to suppress a decrease in magnetic balance caused by uneven winding of the wire. As a result, it is possible to reduce the insertion loss particularly in the high range. In the present invention, the “first winding” and the “second winding” do not define the primary side and the secondary side. It does not matter which winding is connected to the unbalanced transmission line or the balanced transmission line.

  In the present invention, it is preferable that the first winding is wound substantially evenly in the area where the second winding is wound in the core portion. According to this, since the first winding is wound almost uniformly with respect to the second winding, it is possible to obtain a high magnetic balance.

  In the present invention, it is preferable that the first winding is wound on the outer peripheral side of the core part and the second winding is wound on the inner peripheral side of the core part. According to the present invention, since the first winding with a small number of turns is wound on the second winding with a large number of turns, the second winding wound first is the first winding. A guide for winding the winding. For this reason, it is possible to perform a stable winding operation.

  In this case, the parallel winding portion of the first winding is preferably wound along a trough formed by the second winding wound on the inner peripheral side. This makes it possible to reliably wind the parallel winding portion in parallel with the second winding.

  In the present invention, it is preferable that the first winding has a plurality of cross turns and the number of cross turns is equal to the number of turns of the first winding. According to this, since the uniformity of the first winding is increased, it is possible to obtain a good magnetic balance. In this case, it is preferable that the first winding is wound so that a plurality of cross winding portions appear periodically. According to this, since the uniformity of the first winding is further improved, it is possible to obtain a better magnetic balance.

  In the present invention, the cross section in the radial direction of the core portion is polygonal, whereby a plurality of corner portions extending in the axial direction are present on the surface of the core portion, and the parallel winding portion and the cross winding portion are present. It is preferable that the boundary of a part is located in a corner | angular part. According to this, since the boundary between the parallel winding portion and the cross winding portion is fixed to the corner portion of the core portion, stable characteristics can be obtained.

  In this case, the first boundary that changes from the parallel winding portion to the cross winding portion and the second boundary that changes from the cross winding portion to the parallel winding portion are formed on the surface of the core portion. Of the plurality of corners, the first corner where the first boundary is located and the second corner where the second boundary is located are preferably adjacent in the circumferential direction. According to this, it becomes possible to set the length of the cross winding part shorter. In particular, of the sides constituting the polygon, the side located between the first and second corners is preferably shorter than at least one of the other sides. According to this, it becomes possible to set the length of a cross winding part still shorter.

  Thus, according to the present invention, a decrease in magnetic coupling that occurs at the cross winding portion is suppressed, and a decrease in magnetic balance that occurs due to uneven winding of the first and second windings is suppressed. Therefore, various characteristics of the balun transformer using the drum-type core are improved, and it becomes possible to reduce the insertion loss particularly in a high region.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic perspective view showing the appearance of a balun transformer according to a first embodiment of the present invention. FIG. 2 is a schematic bottom view of the balun transformer according to the present embodiment as viewed from the mounting surface side.

  As shown in FIGS. 1 and 2, the balun transformer 100 according to the present embodiment includes a drum core 110, a plate core 120, and two windings 131 and 132. The drum-type core 110 has a core 111 and a pair of flanges 112 and 113 provided at both ends of the core 111. One terminal 112 is provided with two terminal electrodes 141 and 142, and the other terminal 113 is provided with two terminal electrodes 143 and 144.

  The plate-like core 120 is disposed so as to connect the upper portions of the flange portions 112 and 113 of the drum core 110. Although it is not essential to use the plate core 120 in the present invention, if a closed magnetic circuit is formed by using the plate core 120, high magnetic coupling can be obtained. The drum core 110 and the plate core 120 are made of a magnetic material and are not particularly limited, but it is preferable to use a NiZn-based ferrite material. This is because NiZn-based ferrite not only has a relatively high magnetic permeability, but also has a low conductivity, so that a terminal electrode can be directly formed. However, for the plate-like core 120 on which no terminal electrode is formed, an MgZn ferrite material having higher magnetic permeability can be used.

  As shown in FIG. 2, the two windings 131 and 132 are both wound clockwise (in the clockwise direction) toward the arrow A. FIG. 3 is a schematic diagram for explaining a connection relationship between the windings 131 and 132 and the terminal electrodes 141 to 144. As shown in FIG. 3, one end 131 a of the winding 131 is connected to the terminal electrode 141, and the other end 131 b is connected to the terminal electrode 143. In the present embodiment, the winding 131 has six turns. One end 132 a of the winding 132 is connected to the terminal electrode 142, and the other end 132 b is connected to the terminal electrode 144. In the present embodiment, the number of turns of the winding 132 is 14 turns. Thus, in the present embodiment, the winding 132 has more turns than the winding 131.

  FIG. 4 is an equivalent circuit diagram of the balun transformer 100 according to the present embodiment.

  As shown in FIG. 4, the balun transformer 100 according to the present embodiment includes a primary winding L1 connected between the primary side terminal P and the ground terminal GND, a secondary side positive terminal ST, and a secondary side negative electrode. The secondary winding L2 is connected between the terminal SB. In the present embodiment, the winding 131 constitutes the primary winding L1, and the winding 132 constitutes the secondary winding L2. Therefore, the terminal electrode 141 is used as the primary terminal P, the terminal electrodes 142 and 144 are used as the secondary positive terminal ST and the secondary negative terminal SB, respectively, and the terminal electrode 143 is used as the ground terminal GND. However, the primary side and the secondary side may be used as the reverse of the above.

  FIG. 5 is a sectional view in the radial direction of the core 111 of the drum core 110.

  As shown in FIG. 5, the cross section in the radial direction of the core part 111 is substantially rectangular. Therefore, the winding core part 111 has winding surfaces 111a and 111b that constitute long sides (length L1) and winding surfaces 111c and 111d that constitute short sides (length L2). With this shape, there are four corner portions 111ac, 111bc, 111ad, and 111bd extending in the axial direction on the surface of the core portion 111. However, the corner may be rounded to some extent.

  FIG. 6 is a development view of the core 111 of the drum core 110. 7 is a schematic cross-sectional view along the line BB shown in FIG.

  In FIG. 6, the winding 132 wound on the inner peripheral side (that is, the lower layer side) is indicated by a broken line, and the winding 131 wound on the outer peripheral side (that is, the upper layer side) is indicated by a solid line. Yes. The winding 131 is hatched for easy viewing. In addition, an area C shown in FIG. 6 is an area where the winding 132 is wound around the core 111.

  As shown in FIG. 6, the winding 132 located on the inner peripheral side is tightly wound in the area C of the core portion 111 with almost no gap. For this reason, as shown in FIG. 7, valley lines 132 x formed by the winding 132 are formed on the surface of the winding 132 wound around the winding core portion 111. Of course, the valley line 132 x is parallel to the winding 132.

  As shown in FIG. 6, the winding 131 wound around the outer peripheral side is wound along the valley line 132x on the winding surfaces 111a, 111b, and 111d. As a result, portions of the winding 131 wound around the winding surfaces 111 a, 111 b, and 111 d constitute a parallel winding portion 131 x that is wound in parallel along the winding 132. On the other hand, a portion wound around the winding surface 111c, that is, a portion wound between two adjacent corner portions 111ac and 111bc, is a cross winding portion 131y where the winding 131 intersects the winding 132. Configure. Therefore, the winding 131 changes from one end 131a toward the other end 131b at the corner portion 111ac from the parallel winding portion 131x to the cross winding portion 131y, and at the corner portion 111bc from the cross winding portion 131y to the parallel winding portion 131x. Will change.

  The reason why such a cross winding part 131y is provided is that the number of turns of the winding 131 (6 turns) is smaller than the number of turns of the winding 132 (14 turns). That is, when the entire winding 131 is a parallel winding portion 131x without providing such a cross winding portion 131y, the winding is wound only on one side (or only a part of the center) of the area C as shown in FIG. 131 concentrates and magnetic balance falls remarkably. On the other hand, if the cross winding part 131y is provided in addition to the parallel winding part 131x, the winding 131 can be wound almost uniformly in the area C as shown in FIG.

  Even when the cross winding portions 131y are provided, if the number thereof is extremely small, the uniformity of the windings 131 in the area C is lowered as shown in FIG. The example shown in FIG. 9 is an example in which the number of cross winding portions 131y is only one. In such a case, it is difficult to obtain a good magnetic balance. Therefore, it is desirable that the number of cross winding portions 131y be large to some extent, and in particular, winding so that the cross winding portions 131y appear periodically. Is more desirable. Although not particularly limited, it is preferable that the number of the cross winding portions 131y matches the number of turns of the winding 131. In the present embodiment, as shown in FIG. 6, the number of cross winding portions 131 y (six locations) matches the number of turns (6 turns), and the cross winding portions 131 y appear periodically. This is an ideal pattern.

  On the other hand, as shown in FIG. 10, when the entire winding 131 is formed as a cross winding portion 131 y without providing the parallel winding portion 131 x, there is no portion where the winding 131 and the winding 132 are parallel to each other. Overall, the magnetic coupling is reduced. On the other hand, if the parallel winding part 131x and the cross winding part 131y are mixed as in the present embodiment, it is possible to ensure high magnetic coupling while winding the winding 131 in the area C almost uniformly. It becomes possible.

  Thus, in this embodiment, the part wound by winding surface 111a, 111b, 111d among the windings 131 comprises the parallel winding part 131x, and the part wound by the winding surface 111c Constitutes the cross winding part 131y. Here, as shown in FIG. 5, if the length of the winding surfaces 111a and 111b in the circumferential direction is L1, and the length of the winding surfaces 111c and 111d in the circumferential direction is L2, winding for one turn is performed. Among the wires 131, the length of the parallel winding portion 131x is defined by 2 × L1 + L2, and the length of the cross winding portion 131y is defined by L2 (however, the winding 132 wound on the inner peripheral side) I ignored the diameter. Therefore, the parallel winding portion 131x is always longer than the cross winding portion 131y.

  In particular, in the present embodiment, the cross winding portion 131y of the winding 131 is located only on one winding surface 111c, and the winding surface 111c has a short side on the short side in the circumferential direction. Therefore, the length of the cross winding part 131y can be made very short with respect to the length of the parallel winding part 131x.

  Thus, in the balun transformer 100 according to the present embodiment, the winding 131 having a small number of turns is constituted by the parallel winding part 131x and the cross winding part 131y, and the parallel winding part 131x is longer than the cross winding part 131y. Since the winding is performed in such a manner, it is possible to suppress a decrease in magnetic balance caused by uneven winding of the windings 131 and 132 while suppressing a decrease in magnetic coupling that occurs in the cross winding part 131y. It becomes possible. As a result, it is possible to reduce the insertion loss particularly in the high range.

  In addition, since the winding 131 is wound almost uniformly in the area C around which the winding 132 is wound in the winding core portion 111, a high magnetic balance can be obtained. Further, since the winding 131 having a small number of turns is wound on the outer peripheral side of the core part 111 and the winding 132 having a large number of turns is wound on the inner peripheral side of the core part 111, the winding 132 is wound. The winding 131 can be wound with the valley line 132x formed by the guide as a guide. In addition, a portion wound along the valley line 132x becomes a parallel winding portion 131x, and can be reliably wound in parallel with the winding 132.

  Furthermore, in this embodiment, since the cross winding part 131y is located only on one winding surface 111c on the short side among the four winding surfaces 111a to 111d, the parallel winding part 131x. It becomes possible to make the length of the cross winding part 131y very short with respect to the length of.

  In the above embodiment, as shown in FIG. 6, the cross winding part 131y is located only on the winding surface 111c. However, as shown in FIG. 11, the cross winding part 131y is placed on the winding surface 111c. , 111d may be alternately positioned. In the example shown in FIG. 11 as well, the number of cross winding portions 131y (six locations) matches the number of turns (6 turns), and the cross winding portions 131y appear periodically, which is favorable. It is possible to obtain characteristics.

  When the difference in the number of turns of the windings 131 and 132 is large, the cross winding part 131y may be positioned on the winding surface 111b on the long side as shown in FIG. In the example shown in FIG. 12, the winding 131 has 4 turns and the winding 132 has 14 turns.

  When the cross winding part 131y is positioned on the winding surface 111b on the long side, the length of the cross winding part 131y is slightly longer, but the boundary between the parallel winding part 131x and the cross winding part 131y is The stress applied to the winding 131 at the corners 111bc and 111bd can be reduced. That is, when the difference in the number of turns of the windings 131 and 132 is large, the angle formed by the winding 131 and the winding 132 is increased in the cross winding portion 131y. Therefore, the parallel winding portion 131x and the cross winding portion 131y The stress applied to the winding 131 is increased at the corner portion that becomes the boundary. As a result, the winding position of the winding 131 may be shifted, and in some cases, the reliability such as disconnection may be reduced.

  In such a case, as shown in FIG. 12, if the cross winding part 131y is arranged on the winding surface 111b on the long side, the angle formed between the winding 131 and the winding 132 in the cross winding part 131y is small. Therefore, the stress applied to the winding 131 at the corner portions 111bc and 111bd is relieved. As a result, it is possible to prevent the occurrence of deviations in winding positions and disconnection.

  Next, a second preferred embodiment of the present invention will be described.

  As shown in FIG. 13, the present embodiment is different from the balun transformer according to the first embodiment in that the core section 211 has a hexagonal cross section in the radial direction. Since the other points are the same as those of the balun transformer according to the first embodiment, a duplicate description is omitted. As shown in FIG. 13, in this embodiment, the winding core part 211 has six winding surfaces 211a-211f, and among these, the winding surfaces 211a-211d constitute long sides, The surfaces 211e and 211f constitute short sides.

  FIG. 14 is a development view of the core part 211. Also in FIG. 14, the winding 132 wound on the inner peripheral side (that is, the lower layer side) is indicated by a broken line, and the winding 131 wound on the outer peripheral side (that is, the upper layer side) is indicated by a solid line. Yes.

  As shown in FIG. 14, also in the present embodiment, the winding 132 positioned on the inner peripheral side is densely wound in the area C of the core portion 211 with almost no gap. The winding 131 wound on the outer peripheral side is wound along the valley line on the winding surfaces 211a to 211d and 211f, and is wound so as to intersect the winding 132 on the winding surface 211e. Accordingly, in the winding 131, the portion wound around the winding surfaces 211a to 211d, 211f constitutes the parallel winding portion 131x, and the portion wound around the winding surface 211e constitutes the cross winding portion 131y. Will do.

  Thereby, since the length of the cross winding part 131y can be shortened, in addition to the effect by 1st Embodiment, it becomes possible to obtain a more favorable characteristic.

  Further, when the difference in the number of turns of the windings 131 and 132 is large, the cross winding part 131y may be positioned on the two winding surfaces 211c and 211e as shown in FIG. In the example shown in FIG. 15, the winding 131 has 4 turns and the winding 132 has 14 turns. When the cross winding part 131y is positioned on the two winding surfaces 211c and 211e, the length of the cross winding part 131y is slightly longer. However, as described with reference to FIG. 12, the parallel winding part 131x and The stress applied to the winding 131 at the corner that becomes the boundary with the cross winding part 131y can be alleviated.

  Next, a preferred third embodiment of the present invention will be described.

  As shown in FIG. 16, the present embodiment is different from the balun transformer according to the first embodiment in that the cross section in the radial direction of the core portion 311 is a circular shape having a notch (in this example, an oval shape). ing. Since the other points are the same as those of the balun transformer according to the first embodiment, a duplicate description is omitted. As shown in FIG. 16, in this embodiment, the winding core portion 311 has a winding surface 311a that is a curved surface and a winding surface 311b that is a flat surface, and the boundary portions thereof are corner portions 311c, 311d is configured.

  FIG. 17 is a development view of the core portion 311. Also in FIG. 17, the winding 132 wound on the inner peripheral side (that is, the lower layer side) is indicated by a broken line, and the winding 131 wound on the outer peripheral side (that is, the upper layer side) is indicated by a solid line. Yes.

  As shown in FIG. 17, also in this embodiment, the winding 132 positioned on the inner peripheral side is tightly wound in the area C of the core portion 311 with almost no gap. The winding 131 wound on the outer peripheral side is wound along the valley line on the winding surface 311a, and wound so as to intersect the winding 132 on the winding surface 311b. Accordingly, in the winding 131, the portion wound around the winding surface 311a constitutes the parallel winding portion 131x, and the portion wound around the winding surface 311b constitutes the cross winding portion 131y. .

  In this way, even if the majority of the winding core portion is a curved surface, if the two corner portions 311c and 311d are formed by forming a part of the curved portion, the parallel winding portion 131x and the cross winding portion are formed. It becomes possible to fix the boundary of the part 131y to the corner of the core part.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, it is included in the range.

  For example, in each of the above embodiments, the center tap is not provided on the secondary side, but the present invention can also be applied to a balun transformer having a center tap.

  Moreover, in each said embodiment, although the boundary of the parallel winding part 131x and the cross winding part 131y is being fixed to the corner | angular part of a winding core part, the boundary of the parallel winding part 131x and the cross winding part 131y is used. The fixing method is not limited to this. For example, a groove or a protrusion that serves as a guide for the winding with the smaller number of turns (winding 131 in the above example) is formed on the winding core, and the winding with the smaller number of turns is formed along this. You can wind it first.

  Hereinafter, although the Example of this invention is described, this invention is not limited to this Example at all.

  First, the balun transformer of the Example which has the same structure as 1st Embodiment mentioned above was prepared. As already described, the windings 131 and 132 are wound by the method shown in FIG. On the other hand, a balun transformer of the same comparative example as the balun transformer of the embodiment was prepared except that the windings 131 and 132 were wound by the method shown in FIG. That is, both differ only in the winding method of the coil | winding 131, and all others are the same. Note that NiZn ferrite was used as the material for the drum core and the plate core.

  Next, frequency characteristics of insertion loss were measured for the balun transformer of the example and the balun transformer of the comparative example. The measurement results are shown in FIG.

  As shown in FIG. 18, in the balun transformer of the example, the insertion loss is small over a high range, and good characteristics are obtained. On the other hand, in the balun transformer of the comparative example, the increase in insertion loss was remarkable as the frequency increased.

1 is a schematic perspective view showing an appearance of a balun transformer 100 according to a first embodiment of the present invention. It is the approximate bottom view which looked at the balun transformer 100 from the mounting surface side. It is a schematic diagram for demonstrating the connection relation of the windings 131 and 132 and the terminal electrodes 141-144. 2 is an equivalent circuit diagram of the balun transformer 100. FIG. 3 is a cross-sectional view in the radial direction of a core part 111 of the drum core 110. FIG. 3 is a development view of the core 111 of the drum core 110. FIG. 7 is a schematic cross-sectional view along the line BB shown in FIG. 6. It is a figure which shows the example which concentrated the coil | winding 131 only on the one side of the area C. FIG. It is a figure which shows the example which made the number of cross winding parts 131y only one place. It is a figure which shows the example which made the whole winding 131 the cross winding part 131y. It is a figure which shows the example which alternately located the cross winding part 131y on the winding surfaces 111c and 111d. It is a figure which shows the example which located the cross winding part 131y in the winding surface 111b. It is sectional drawing in the radial direction of the core part 211 in the 2nd Embodiment of this invention. FIG. 6 is a development view of the core part 211. It is a figure which shows the example which located the cross winding part 131y over winding surface 211c, 211e. It is sectional drawing in the radial direction of the core part 311 in the 3rd Embodiment of this invention. It is an expanded view of the core part 311. It is a graph which shows the measurement result of insertion loss.

Explanation of symbols

100 Balun transformer 110 Drum type cores 111, 211, 311 Core portions 111a to 111d, 211a to 211f, 311a, 311b Winding surfaces 111ac, 111bc, 111ad, 111bd, 311c, 311d Corner portions 112, 113 ridge portion 120 Plate shape Core 131, 132 Winding 131a, 132a Winding end 131b, 132b Winding other end 131x Parallel winding portion 131y Cross winding portion 132x Valley wires 141-144 Terminal electrode GND Ground terminal L1 Primary winding L2 Secondary Winding P Primary side terminal ST Secondary side positive terminal SB Secondary side negative terminal

Claims (9)

A drum core having a core portion and a pair of flange portions provided at both ends of the core portion, a plurality of terminal electrodes provided in the flange portion, and both ends wound around the core portion and the terminals First and second windings connected to the electrodes;
The number of turns of the second winding is greater than the number of turns of the first winding,
The first winding includes a parallel winding portion wound in parallel along the second winding, and a cross winding portion wound so as to intersect with the second winding. The balun transformer is characterized in that the parallel winding portion is longer than the cross winding portion.   2. The balun transformer according to claim 1, wherein the first winding is wound substantially uniformly in an area of the winding core portion where the second winding is wound.   The said 1st coil | winding is wound by the outer peripheral side of the said core part, and the said 2nd coil | winding is wound by the inner peripheral side of the said core part. The balun transformer described in.   The parallel winding portion of the first winding is wound along a trough formed by the second winding wound on the inner peripheral side. 3. A balun transformer according to 3.   The first winding has a plurality of the cross winding portions, and the number of the cross winding portions is equal to the number of turns of the first winding. A balun transformer according to claim 1.   The balun transformer according to claim 5, wherein the first winding is wound such that the plurality of cross winding portions appear periodically. The core section has a polygonal cross-section in the radial direction, whereby there are a plurality of corners extending in the axial direction on the surface of the core section,
The balun transformer according to any one of claims 1 to 6, wherein a boundary between the parallel winding portion and the intersecting winding portion is located at the corner portion. The boundary includes a first boundary that changes from the parallel winding portion to the cross winding portion, and a second boundary that changes from the cross winding portion to the parallel winding portion,
Of the plurality of corner portions formed on the surface of the core portion, the first corner portion where the first boundary is located and the second corner portion where the second boundary is located are in the circumferential direction. The balun transformer according to claim 7, which is adjacent to each other.   The side located between the first and second corners among the sides constituting the polygon is a side shorter than at least one of the other sides. Balun Trans.

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