Patent Publication Number: US-9852841-B2

Title: Coil structure, transformer, and power converter

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2014-011966, filed on Jan. 27, 2014, the contents of which are hereby incorporated by reference. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a coil structure, a transformer including the coil structure, and a power converter including the coil structure. 
     2. Description of the Related Art 
     Japanese Unexamined Patent Application Publication No. 2011-9433 discloses a coil constituted by a sheet-like conductor wire. In this coil, the sheet-like conductor wire is folded in multiple portions such that the front side and the back side are alternately reversed. Japanese Unexamined Patent Application Publication No. 2013-21307 discloses a coil constituted by a band conductor sheet. In this coil, the band conductor sheet is folded over on the front side or the back side multiple times. 
     SUMMARY 
     In the related art, there is a demand for a coil structure which can be easily formed. Accordingly, one non-limiting and exemplary embodiment provides a coil structure which can be easily formed, a transformer including this coil structure, and a power converter including this coil structure. 
     One aspect of the present disclosure provides a coil structure including a conductor band and a first insulating plate. The conductor band includes a plurality of folded portions. The conductor band turns around a coil axis while being folded at a plurality of folded portions. The first insulating plate includes a first edge portion which abuts along at least one of the plurality of folded portions. At least part of the conductor band is wound around the first insulating plate. 
     These comprehensive and specific aspects may be implemented using a transformer, a power converter, a system, or a manufacturing method, or any combination of transformers, power converters, systems, and manufacturing methods. 
     A coil structure, a transformer, and a power converter according to one aspect of the present disclosure are easily manufactured. 
     Additional benefits and advantages of the disclosed embodiments will be apparent from the specification and drawings. The benefits and/or advantages may be individually provided by the various embodiments and features of the specification and drawings disclosure, and need not all be provided in order to obtain one or more of the same. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flowchart illustrating an example of a manufacturing method for a coil structure according to a first embodiment; 
         FIG. 2A  is a schematic perspective view illustrating an example of a conductor band; 
         FIG. 2B  is a schematic plan view of the conductor band shown in  FIG. 2A ; 
         FIG. 2C  is a schematic side view of the conductor band shown in  FIG. 2A ; 
         FIG. 2D  is a sectional view taken along line IID-IID of  FIG. 2B ; 
         FIG. 3A  is a schematic perspective view illustrating a known edgewise coil; 
         FIG. 3B  is a schematic plan view illustrating the edgewise coil shown in  FIG. 3A ; 
         FIG. 3C  is a schematic side view illustrating the edgewise coil shown in  FIG. 3A ; 
         FIG. 4  is a schematic perspective view illustrating part of the conductor band shown in  FIG. 2A ; 
         FIG. 5  is a schematic perspective view illustrating an example of an insulating plate; 
         FIG. 6  is a schematic perspective view illustrating an example of a coil structure according to a second embodiment; 
         FIG. 7  is a schematic perspective view illustrating an example of a coil structure according to a third embodiment; 
         FIG. 8  is a schematic perspective view illustrating an example of a coil structure according to a fourth embodiment; 
         FIG. 9  is a schematic perspective view illustrating an example of an insulating plate included in the coil structure shown in  FIG. 8 ; 
         FIG. 10A  is a schematic sectional view illustrating a magnetic casing included in the coil structure shown in  FIG. 8 ; 
         FIG. 10B  is a schematic sectional view of the coil structure taken along line XB-XB of  FIG. 10A ; 
         FIG. 10C  is a schematic sectional view of the coil structure taken along line XC-XC of  FIG. 10A ; 
         FIGS. 11A through 11H  are schematic views illustrating examples of steps for folding a conductor band; 
         FIGS. 12A through 12E  are schematic views illustrating examples of steps for folding a conductor band; 
         FIG. 13A  is a schematic perspective view illustrating an example of an insulating plate; 
         FIG. 13B  is a schematic plan view illustrating the insulating plate shown in  FIG. 13A ; 
         FIG. 13C  is a schematic sectional view taken along line XIIIC-XIIIC of  FIG. 13B ; 
         FIG. 14A  is a schematic perspective view illustrating an example of an insulating plate; 
         FIG. 14B  is a schematic plan view illustrating the insulating plate shown in  FIG. 14A ; 
         FIG. 14C  is a schematic sectional view taken along line XIVC-XIVC of  FIG. 14B ; 
         FIG. 15  is an exploded sectional view illustrating a coil structure formed by using the insulating plate shown in  FIG. 14A ; 
         FIG. 16A  is a schematic perspective view illustrating an example of a conductor band; 
         FIG. 16B  is a schematic plan view illustrating the conductor band shown in  FIG. 16A ; 
         FIG. 17A  is a schematic perspective view illustrating an example of an insulating plate which is combined with the conductor band shown in  FIG. 16A ; 
         FIG. 17B  is a schematic plan view illustrating the insulating plate shown in  FIG. 17A ; 
         FIG. 18A  is a schematic perspective view illustrating an example of a coil structure; 
         FIG. 18B  is a schematic plan view illustrating the coil structure shown in  FIG. 18A ; 
         FIG. 19  is a schematic perspective view illustrating an example of an insulating plate; 
         FIG. 20  is a schematic perspective view illustrating an example of a folding pattern of a plurality of conductor bands; 
         FIGS. 21A through 21H  are schematic views illustrating examples of steps for folding first and second conductor bands; 
         FIG. 22  is a schematic perspective view illustrating an example of a coil structure; 
         FIG. 23  is a schematic perspective view illustrating an example of a folding pattern of first and second conductor bands; and 
         FIG. 24  is a schematic block diagram illustrating an example of a power converter. 
     
    
    
     DETAILED DESCRIPTION 
     (Underlying Knowledge Forming Basis of the Present Disclosure) 
     A coil constituted by magnet wire or litz wire is not suitable for a large-current use. In contrast, an edgewise coil constituted by conductive flat wire is suitable for a large-current use. 
     An edgewise coil is constituted by flat wire which turns around a coil axis, such as that shown in  FIG. 3A . The edgewise coil includes an inner peripheral edge closer to the coil axis and an outer peripheral edge farther away from the coil axis. The inner peripheral portion, which is shorter than the outer peripheral edge, has a lower electrical resistance than the outer peripheral edge. Accordingly, a current is more likely to concentrate on the inner peripheral portion. As a result, large resistive losses may occur in the edgewise coil. 
     Japanese Unexamined Patent Application Publication Nos. 2011-9433 and 2013-21307 disclose known coils constituted by a band conductor sheet. Band conductor sheets are suitable for a large-current use, as in an edgewise coil. However, the shapes of coils formed based on these publications are not stably maintained. If a physical force, for example, a self-weight or another compressive force, is applied to the coil, some portions of the band conductor sheet of the coil may be in contact with each other. Accordingly, it is required for these coils to include an insulating film which covers the surface of the band conductor sheet. This increases the complexity of the manufacturing steps for these coils. Additionally, since an insulating film is folded together with the band conductor sheet, it may also be damaged. 
     In order to solve at least one of the above-described problems, the present inventors have conducted intensive and extensive study concerning a large-current-use coil which can be easily formed. 
     Overview of Embodiment 
     A coil structure according to an aspect of the present disclosure includes a conductor band and a first insulating plate. The conductor band includes a plurality of folded portions. The conductor band turns around a coil axis while being folded at a plurality of folded portions. The first insulating plate includes a first peripheral edge portion which abuts along at least one of the plurality of folded portions. At least part of the conductor band being wound around the first insulating plate. 
     With the above-described configuration, since at least part of the conductor band is wound around the first insulating plate, the shape of the coil structure is stably maintained. It is thus less likely that some regions of the conductor band of the coil structure will be in contact with each other. The first edge portion of the first insulating plate abuts along at least one of the plurality of folded portions. This enables a manufacturer manufacturing the coil structure to fold the conductor band by using the first edge portion. It is thus possible for the manufacturer to manufacture the coil structure easily. 
     In a coil structure according to an aspect of the present disclosure, the conductor band may include a first band surface and a second band surface opposite to the first band surface. The plurality of folded portions may include a plurality of first folded parts in each of which part of the first band surface is folded inwardly and a plurality of second folded parts in each of which part of the second band surface is folded inwardly. Each of the plurality of first folded parts and each of the plurality of second folded parts may be alternately disposed in a direction in which the conductor band extends. 
     With the above-described configuration, since the first and second folded parts are alternately disposed, the difference of the electrical length can be reduced in the coil structure, thereby decreasing the electrical resistance of the coil structure. 
     A coil structure according to an aspect of the present disclosure may further include a second insulating plate opposed to the first insulating plate. The conductor band may include a first band surface and a second band surface opposite to the first band surface. The plurality of folded portions may include a first folded part where part of the first band surface is folded inwardly and a second folded part where part of the second band surface is folded inwardly. The first insulating plate may include the first edge portion which abuts along the first folded part. The second insulating plate may include a second edge portion which abuts along the second folded part. The conductor band may include a band portion which extends between the first and second folded parts. The band portion may be sandwiched between the first and second insulating plates. 
     With the above-described configuration, a manufacturer can form the first folded part by using the first edge portion and form the second folded part by using the second edge portion. It is thus possible for the manufacturer to manufacture the coil structure easily. 
     A coil structure according to an aspect of the present disclosure may further include a plurality of insulating plates including the first insulating plate. The plurality of insulating plates may be as many as or greater than the plurality of folded portions. 
     With the above-described configuration, the plurality of folded portions may be wound around different insulating plates, thereby stably maintaining the shape of the coil structure. 
     A coil structure according to an aspect of the present disclosure may further include: a first plurality of insulating plates including the first insulating plate; a second plurality of insulating plates; and a second conductor band. The plurality of folded portions may include a plurality of first folded portions and a plurality of second folded portions. The conductor band may include a first turn section that turns around the coil axis through one revolution while being folded at the plurality of first folded portions, and a second turn section that turns around the coil axis through one revolution while being folded at the plurality of second folded portions, the second turn section being connected to one end of the first turn section. The first turn section may be wound around the first plurality of insulating plates, and the second turn section may be wound around the second plurality of insulating plates. 
     With the above-described configuration, the first plurality of insulating plates around which the first turn section is wound is different from the second plurality of insulating plates around which the second turn section is wound. Thus, it is less likely that the first turn section and the second turn section will be in contact with each other. 
     A coil structure according to an aspect of the present disclosure may further include a magnetic core extending in a direction along the coil axis. The first insulating plate may include a first axial hole through which the magnetic core passes, and the second insulating plate may include a second axial hole through which the magnetic core passes. 
     With the above-described configuration, due to the provision of a magnetic core inserted into the first and second axial holes, high inductance can be exhibited. 
     In a coil structure according to an aspect of the present disclosure, a configuration of the magnetic core may be complementary to a configuration of each of the first and second axial holes, and the configuration of each of the first and second axial holes may be noncircular. 
     With the above-described configuration, the insulating plate does not unnecessarily rotate around the magnetic core. It is thus possible for a manufacturer to manufacture the coil structure easily by using the magnetic core. 
     In a coil structure according to an aspect of the present disclosure, the first insulating plate may include a first principal surface and a second principal surface opposite to the first principal surface. The first edge portion may be part of a side surface which connects a contour of the first principal surface and a contour of the second principal surface. 
     With the above-described configuration, the conductor band is wound around the outer periphery of the first insulating plate. It is thus possible for a manufacturer to manufacture the coil structure easily. 
     In a coil structure according to an aspect of the present disclosure, the first insulating plate may include a through-hole through which the conductor band passes, and the first edge portion may be part of an inner peripheral surface which defines the through-hole. 
     With the above-described configuration, it is possible for a manufacturer or a designer to set a long creepage distance between the coil structure and a component disposed near the coil structure. 
     In a coil structure according to an aspect of the present disclosure, the conductor band may include a first band surface and a second band surface opposite to the first band surface. The plurality of folded portions may include a plurality of folded parts in each of which part of the first band surface is folded inwardly. The conductor band may include a turn section that turns around the coil axis through one revolution while being folded at the plurality of folded parts. The first insulating plate may include a plurality of edge portions including the first edge portion. The plurality of folded parts may be folded along the plurality of edge portions. 
     With the above-described configuration, it is possible for a manufacturer to wind the plurality of folded parts included in the turn section along the plurality of edge portions of the first insulating plate. It is thus possible to reduce the number of insulating plates around which the turn section is wound. 
     A coil structure according to an aspect of the present disclosure may further include a second insulating plate. The conductor band may include a band portion which extends between the plurality of folded portions. The band portion may be sandwiched between the first and second insulating plates. At least one of the first and second insulating plates may include a holding section for holding the band portion therein, at a position at which the holding section opposes the band portion. 
     With the above-described configuration, since the band portion is held within the holding section, the distance between the first and second insulating plates is decreased, thereby making it possible to form the coil structure thin. 
     In a coil structure according to an aspect of the present disclosure, the plurality of folded portions may include five or more folded portions. The conductor band may include a turn section that turns around the coil axis through one revolution while being folded at the five or more folded portions. Each of the plurality of first folded parts and each of the plurality of second folded parts may be alternately disposed in a direction in which the turn section extends. 
     With the above-described configuration, the effect of providing twisted wire is more noticeable, thereby decreasing the electrical resistance of the coil structure. 
     In a coil structure according to an aspect of the present disclosure, the plurality of folded portions may be a first plurality of folded portions, and the conductor band may be a first conductor band. The coil structure may further include a second conductor band that turns around the coil axis while being folded at a second plurality of folded portions. At least one of the second plurality of folded portions may be folded along the first edge portion. 
     With the above-described configuration, a manufacturer manufacturing the coil structure can fold the first and second conductor bands by using the first edge portion. It is thus possible for the manufacturer to manufacture the coil structure easily. 
     In a coil structure according to an aspect of the present disclosure, the plurality of folded portions may be a first plurality of folded portions, and the conductor band may be a first conductor band. The coil structure may further include a second conductor band that turns around the coil axis while being folded at a second plurality of folded portions. The first insulating plate may include a different edge portion from the first edge portion. At least one of the second plurality of folded portions may be folded along the different edge portion. 
     With the above-described configuration, a manufacturer manufacturing the coil structure can fold the first conductor band by using the first edge portion and the second conductor band by using the different edge portion. It is thus possible for the manufacturer to manufacture the coil structure easily. 
     In a coil structure according to an aspect of the present disclosure, the conductor band may include a band portion between two adjacent folded portions which are included in the plurality of folded portions, and a line normal to a principal surface of the band portion (“NL” shown in  FIG. 4 ) may be parallel with the coil axis. 
     Even if a principal surface of the band portion is parallel with the coil axis, since a coil is formed by partially folding the conductor band at a plurality of portions, the difference of the electrical length of the entire coil can be reduced. 
     In a coil structure according to an aspect of the present disclosure, the insulating plate may have a higher folding stiffness than the conductor band. 
     With this configuration, the conductor band is more easily folded than the insulating plate. It is thus possible for a manufacturer to manufacture the coil structure easily. 
     A transformer according to an aspect of the present disclosure includes the above-described coil structure including the first conductor band and the second conductor band. When a current is supplied to one of the first and second conductor bands, an induced current is generated in the other one of the first and second conductor bands. 
     With the above-described configuration, it is possible to easily manufacture a transformer. 
     A power converter according to an aspect of the present disclosure includes the above-described coil structure and a switching circuit including a switching element. 
     With the above-described configuration, it is possible to easily manufacture a power converter. 
     A manufacturing method for a coil structure according to an aspect of the present disclosure includes: preparing a conductor band and at least one insulating plate including a first insulating plate; and winding the conductor band around the at least one insulating plate. In the step of winding, the conductor band is folded along a first edge portion of the first insulating plate to sandwich the first insulating plate between portions of the conductor band therebetween. 
     A manufacturing method for a coil structure according to an aspect of the present disclosure includes: preparing a conductor band and a plurality of insulating plates including a first insulating plate, a second insulating plate, and a third insulating plate; disposing the first insulating plate on a first band portion included in the conductor band; folding the conductor band along a first edge portion of the first insulating plate to form a first folded portion, a first remaining portion which is connected to the first folded portion at a position opposite the first band portion; disposing the second insulating plate on a second band portion included in the first remaining portion to sandwich the second band portion between the first and second insulating plates; folding the first remaining portion along a second edge portion of the second insulating plate to form a second folded portion and a second remaining portion which is connected to the second folded portion at a position opposite the second band portion; disposing the third insulating plate on a third band portion included in the second remaining portion to sandwich the third band portion between the second and third insulating plates; and folding the second remaining portion along a third edge portion of the third insulating plate to form a third folded portion and a third remaining portion which is connected to the third folded portion at a position opposite the third band portion. 
     A manufacturing method for a coil structure according to an aspect of the present disclosure includes: preparing, for example, a conductor band and an insulating plate; disposing the insulating plate on a first band portion included in the conductor band; folding the conductor band along a first edge portion of the insulating plate to form a first folded portion and a first remaining portion which is connected to the first folded portion at a position opposite the first band portion; folding the first remaining portion along a second edge portion of the insulating plate to form a second folded portion and a second remaining portion which is connected to the second folded portion at a position opposite a second band portion included in the first remaining portion; and folding the second remaining portion along a third edge portion of the insulating plate to form a third folded portion and a third remaining portion which is connected to the third folded portion at a position opposite a third band portion included in the second remaining portion. 
     Various embodiments of a coil structure, a transformer, and a power converter will be described below with reference to the accompanying drawings. The coil structure, the transformer, and the power converter may be clearly understood by the following description. The terms defining directions, such as “top”, “bottom”, “right”, and “left” are given merely for clarifying a description. These terms are not to be interpreted definitely and restrictively. In all the drawings, the same or similar elements are designated by like reference numerals, and an explanation of the same or similar elements designated by a like reference numeral may be given only once. 
     All of embodiments described below illustrate comprehensive or specific examples. Numeric values, configurations, materials, components, arrangement positions of the components, connection states, and manufacturing order illustrated in the following embodiments are only examples, and are not intended to limit the present disclosure. Among the components illustrated in the following embodiments, components that are not recited in the independent claims will be described as optional components. 
     First Embodiment 
       FIG. 1  is a flowchart schematically illustrating an example of a manufacturing method for a coil structure. An example of the manufacturing method for a coil structure will be discussed below with reference to  FIG. 1 . 
     In step S 110 , at least one conductor band and at least one insulating plate are prepared. 
     In step S 120 , the conductor band is wound around the insulating plate. The insulating plate includes an edge portion used for folding the conductor band. As a result, the edge portion of the insulating plate abuts along a folded portion of the conductor band. The conductor band is repeatedly folded such that it turns around the coil axis, and as a result, it is processed into a coil. 
     In the conductor band, as the difference between lengths of a pair of side surfaces extending in the longitudinal direction of the conductor band is smaller, the difference between electrical lengths of portions around these side surfaces is smaller, thereby reducing resistive losses of the coil. 
     In the following embodiments, various folding patterns of conductor bands will be described. These folding patterns are formed by the manufacturing method indicated by the flowchart of  FIG. 1 . The folding patterns of conductor bands in the following embodiments are not restricted to specific folding patterns discussed below. 
     The configuration of an insulating plate may be determined according to the folding pattern of a conductor band. Accordingly, the insulating plates used in the following embodiments are not restricted to specific configurations discussed below. 
     Second Embodiment 
     In a second embodiment, examples of folding patterns will be discussed. 
       FIG. 2A  is a schematic perspective view illustrating a conductor band  200  which is folded by using the manufacturing method of the first embodiment.  FIG. 2B  is a schematic plan view of the conductor band  200 .  FIG. 2C  is a schematic side view of the conductor band  200 .  FIG. 2D  is a sectional view taken along line IID-IID of  FIG. 2B . The conductor band  200  will be described below with reference to  FIGS. 2A through 2D . 
     The conductor band  200  includes a first band surface  210 , a second band surface  220  which opposes the first band surface  210 , and a pair of side surfaces  231  and  232  which connect the first band surface  210  and the second band surface  220 . The conductor band  200  also includes a plurality of folded portions  240  formed by repeatedly folding the conductor band  200  such that it turns around the coil axis CA. The folded portions  240  include a plurality of first folded parts  241  and a plurality of second folded parts  242 . At a first folded part  241 , part of the first band surface  210  is folded inwardly. In other words, at a first folded part  241 , two regions included in the first band surface  210  face each other. At a second folded part  242 , part of the second band surface  220  is folded inwardly. In other words, at a second folded part  242 , two regions included in the second band surface  220  face each other. The first folded parts  241  and the second folded parts  242  are alternately formed along the extending direction of the conductor band  200 . 
       FIG. 3A  is a schematic perspective view illustrating a known edgewise coil  900 .  FIG. 3B  is a schematic plan view illustrating the edgewise coil  900 .  FIG. 3C  is a schematic side view illustrating the edgewise coil  900 . The differences between the conductor band  200  and the edgewise coil  900  will be discussed below with reference to  FIGS. 2A through 3C . 
     The edgewise coil  900  includes a first band surface  910 , a second band surface  920  which opposes the first band surface  910 , and a pair of side surfaces  931  and  932  which connect the first band surface  910  and the second band surface  920 . The coil axis CA is shown in  FIG. 3A , as well as in  FIG. 2A . The side surface  931  turns around the coil axis CA while being constantly located near the coil axis CA. In contrast, the side surface  932  turns around the coil axis CA while being constantly located far away from the coil axis CA. Accordingly, the side surface  931  is noticeably shorter than the side surface  932 . 
       FIG. 2B  illustrates the conductor band  200  on the XY coordinates. The conductor band  200  includes sections extending in the X-axis direction and sections extending in the Y-axis direction. The sections extending in the X-axis direction and the sections extending in the Y-axis direction are alternately formed. Thus, the conductor band  200  is a rectangular coil. 
     In the sections extending in the X-axis direction, the side surface  231  is positioned farther away from the coil axis CA than the side surface  232 . In contrast, in the sections extending in the Y-axis direction, the side surface  231  is positioned closer to the coil axis CA than the side surface  232 . Accordingly, the difference between the length of the side surface  231  and that of the side surface  232  is small. As a result, it is less likely that a current flowing through the conductor band  200  will be biased toward one of the side surfaces  231  and  232 . Thus, resistive losses occurring in the conductor band  200  are smaller than those of the edgewise coil  900 . 
       FIG. 4  is a schematic perspective view illustrating part of the conductor band  200 . A folding pattern of the conductor band  200  will be discussed below with reference to  FIGS. 1 and 4 . 
     The coil axis CA and a reference line RL parallel with the coil axis CA are shown in  FIG. 4 . Intersection points IP 1  and IP 2  between the reference line RL and the conductor band  200  are also shown in  FIG. 4 . Hereinafter, a section of the conductor band  200  from the intersection point IP 1  to the intersection point IP 2  will be referred to as “a turn section”. A portion between the intersection points IP 1  and IP 2  of the conductor band  200  turns around the coil axis CA through one revolution. Typically, the conductor band  200  has a larger sectional area than litz wire, and thus, a larger current can flow through the conductor band  200 . From this point of view, a coil structure may have a small number of turn sections. 
       FIG. 4  shows that four folded portions  240  are formed within one turn section. Accordingly, a manufacturer may prepare four insulating plates per turn section in step S 110  discussed with reference to  FIG. 1 . 
       FIG. 5  is a schematic perspective view illustrating an example of an insulating plate  300  used together with the conductor band  200 . The insulating plate  300  will be discussed below with reference to  FIGS. 4 and 5 . 
     The insulating plate  300  includes a substantially octagonal base portion  310  and four protruding portions  320  protruding from the base portion  310 . The base portion  310  includes four outer peripheral edges  311 . The protruding portions  320  and the outer peripheral edges  311  are alternately arranged. One of the four outer peripheral edges  311  abuts along one of the folded portions  240  shown in  FIG. 4 . Accordingly, the outer peripheral edge  311  can define the folding angle of the folded portion  240 . A pair of protruding portions  320 , between which a folded portion  240  disposed, has surfaces opposing the side surfaces  231  and  232  of the folded portion  240 . Accordingly, the protruding portions  320  can stably maintain the positions of the folded portions  240 . One of the outer peripheral edges  311  is an example of “a first edge portion” of the present disclosure. 
       FIG. 6  is a schematic perspective view illustrating an example of a coil structure  100 . The coil structure  100  will be described below with reference to  FIGS. 4 and 6 . 
     The coil structure  100  includes a coil  120  and an insulating plate structure  130 . The coil  120  may be the conductor band  200  discussed with reference to  FIG. 4 . The insulating plate structure  130  may be an insulating plate array including four insulating plates  300  aligned along the coil axis CA. One insulating plate  300  is disposed such that it is assigned to a folded portion  240 . With this structure, even if a compressive force in the direction of the coil axis CA is applied to the coil structure  100 , it is less likely that some regions of the conductor band  200  will be in contact with each other. 
     Third Embodiment 
     The coil structure  100  of the second embodiment includes one turn section. Alternatively, the coil of the coil structure may include a plurality of turn sections. A designer designing a coil structure may determine the number of turn sections to be included in the coil structure by considering the performance demanded for the coil structure. In a third embodiment, a coil structure including two turn sections will be discussed. 
       FIG. 7  is a schematic perspective view illustrating a coil structure  100 A of the third embodiment. The coil structure  100 A will be described below with reference to  FIG. 7 . Elements having the same functions as those of the second embodiment are designated by like reference numerals, and thus, an explanation thereof will be omitted. 
     The coil structure  100 A includes a coil  120 A and an insulating plate structure  130 A. The coil  120 A may be the conductor band  200  discussed in the second embodiment. The conductor band  200  includes two turn sections. In the following description, one of the two turn sections will be referred to as “a first turn section”, and the other one of the two turn sections will be referred to as “a second turn section”. The first turn section of the conductor band  200  turns around the coil axis CA through one revolution. The second turn section is connected to the first turn section. The second turn section of the conductor band  200  also turns around the coil axis CA through one revolution. 
     The insulating plate structure  130 A may be an insulating plate array constituted by eight insulating plates  300  aligned along the coil axis CA. Four insulating plates  300  are assigned to the first turn section, while the remaining four insulating plates  300  are assigned to the second turn section. 
     In the present disclosure, a plurality of insulating plates assigned to the first turn section may be referred to as “a first plurality of insulating plates”, and a plurality of insulating plates assigned to the second turn section may be referred to as “a second plurality of insulating plates”. In the example shown in  FIG. 7 , a group of the first plurality of insulating plates and a group of the second plurality of insulating plates each constituted by four insulating plates  300 . The first plurality of insulating plates may include, for example, a first insulating plate. In the present disclosure, folded portions included in the first turn section may be referred to as “first folded portions”, and folded portions included in the second turn section may be referred to as “second folded portions”. 
     Fourth Embodiment 
     A coil structure may include a magnetic core extending along the coil axis. Due to the provision of a magnetic core, high inductance can be exhibited. In a fourth embodiment, a coil structure including a magnetic core will be discussed. 
       FIG. 8  is a schematic perspective view illustrating a coil structure  100 B of the fourth embodiment. The coil structure  100 B will be described below with reference to  FIG. 8 . Elements having the same functions as those of the second embodiment are designated by like reference numerals, and thus, an explanation thereof will be omitted. 
     As in the second embodiment, the coil structure  100 B includes a coil  120 . The coil structure  100 B also includes an insulating plate structure  130 B and a magnetic casing  140 . The insulating plate structure  130 B includes a plurality of insulating plates  300 B. The arrangement of the plurality of insulating plates  300 B with respect to the coil  120  is similar to that of the second embodiment. 
       FIG. 9  is a schematic perspective view illustrating an example of the insulating plate  300 B. The insulating plate  300 B will be discussed below with reference to  FIG. 9 . 
     As in the second embodiment, the insulating plate  300 B includes four protruding portions  320 . The insulating plate  300 B also includes a substantially octagonal base portion  310 B. As in the second embodiment, the base portion  310 B includes four outer peripheral edges  311 . In the base portion  310 B, an axial hole  319  is formed. The center of the axial hole  319  substantially coincides with the coil axis CA. In  FIG. 9 , the axial hole  319  is substantially a square. 
       FIG. 10A  is a schematic sectional view illustrating the magnetic casing  140 .  FIG. 10B  is a schematic sectional view of the coil structure  100 B taken along line XB-XB of  FIG. 10A .  FIG. 10C  is a schematic sectional view of the coil structure  100 B taken along line XC-XC of  FIG. 10A . The magnetic casing  140  will be discussed below with reference to  FIGS. 10A through 10C . 
     As in the second embodiment, the plurality of insulating plates  300 B are aligned along the coil axis CA. As a result, the axial hole  319  also extends along the coil axis CA. 
     In the present disclosure, if a first insulating plate included in a plurality of insulating plates has an axial hole, this axial hole may be referred to as “a first axial hole”, and if a second insulating plate included in a plurality of insulating plates has an axial hole, this axial hole may be referred to as “a second axial hole”. 
     The magnetic casing  140  includes an outer wall portion  141  and a magnetic core  142 . The outer wall portion  141  surrounds the insulating plate structure  130 B having the coil  120  fixed thereto. The magnetic core  142  passes through the axial hole  319  along the coil axis CA. The configuration of the magnetic core  142  is complementary to the configuration of the axial hole  319 . Accordingly, the coil  120  and the insulating plate structure  130 B do not unnecessarily rotate around the magnetic core  142 . That is, the magnetic core  142  can define the angles of the coil  120  and the insulating plate structure  130 B so as to position them. 
     The configuration of the axial hole  319  and the configuration of the magnetic core  142  are not restricted to those discussed above. As long as the configurations of the axial hole  319  and the magnetic core  142  are noncircular and are complementary to each other, the magnetic core  142  can suitably position the insulating plate structure  130 B having the coil  120  fixed thereto. 
     Fifth Embodiment 
     In the coil structures  100 ,  100 A, and  100 B of the second, third, and fourth embodiments, respectively, the outer peripheral edges  311  are used for folding a conductor band. Accordingly, the coil structures  100 ,  100 A, and  100 B can be formed by using a simple manufacturing method. In a fifth embodiment, a manufacturing method for a coil structure will be described. 
       FIGS. 11A through 11H  are schematic views illustrating steps for folding the conductor band  200  by using insulating plates. An example of the manufacturing method for the coil structure  100 B will be described below with reference to  FIGS. 1, 2A, 9, and 11A through 11H . Elements having the same functions as those of the fourth embodiment are designated by like reference numerals, and thus, an explanation thereof will be omitted. 
     In step S 110  of  FIG. 1 , a manufacturer prepares a conductor band  200  and insulating plates  301  through  304 . Each of the insulating plates  301  through  304  corresponds to the insulating plate  300 B discussed with reference to  FIG. 9 . 
     Each of the insulating plates  301  through  304  includes edge portions  312  through  315 . The edge portions  312  through  315  correspond to the four outer peripheral portion edges  311  discussed with reference to  FIG. 9 . In  FIGS. 11A through 11H , the edge portion  312  is positioned at the top left as viewed from the coil axis CA, the edge portion  313  is positioned at the top right as viewed from the coil axis CA, the edge portion  314  is positioned at the bottom right as viewed from the coil axis CA, and the edge portion  315  is positioned at the bottom left as viewed from the coil axis CA. Each of the edge portions  312  through  315  form part of the contour of each of the insulating plates  301  through  304 . For example, if the insulating plate  301  has a pair of opposing principal surfaces, the edge portion  312  is part of a side surface connecting the contours of the pair of principal surfaces. 
       FIGS. 11A through 11H  show XY coordinates. Each of the edge portions  312  through  315  is tilted at +45° or −45° with respect to the X axis. The conductor band  200  is sequentially folded along the edge portions  312  through  315 . In the process in which the conductor band  200  is being folded, the conductor band  200  is constituted by a portion extending in the X-axis direction and a portion extending in the Y-axis direction. In the present disclosure, portions of a conductor band other than folded portions may be referred to as “band portions” or “remaining portions”. 
     The conductor band  200  includes a start portion  201  and an end portion  202  opposite to the start portion  201 . The conductor band  200  has one turn section between the start portion  201  and the end portion  202 . 
     The first band surface  210  of the conductor band  200  extending in the Y-axis positive direction is shown in  FIG. 11A . As shown in  FIG. 11A , a manufacturer superposes the insulating plate  301  on the start portion  201 . Then, as shown in  FIG. 11B , the manufacturer folds the conductor band  200  along the edge portion  312  so as to form a folded portion  251 . As a result, around the edge portion  312 , a section of the first band surface  210  in a range from the start portion  201  to the edge portion  312  faces the remaining section of the first band surface  210 . On the other hand, as shown in  FIG. 11B , the second band surface  220  appears on the insulating plate  301  such that it extends from the edge portion  312  in the X-axis positive direction. The folded portion  251  corresponds to the first folded part  241  discussed with reference to  FIG. 2A . 
     In  FIG. 11A , a portion in which the insulating plate  301  and the conductor band  200  are superposed is an example of “a first band portion” in the fifth embodiment. In  FIG. 11B , a portion of the conductor band  200  positioned in front of the insulating plate  301  is an example of “a first remaining portion” in the fifth embodiment. The insulating plate  301  in  FIGS. 11A and 11B  is an example of “a first insulating plate” of the fifth embodiment. 
     After forming the folded portion  251 , as shown in  FIG. 11C , the manufacturer superposes the insulating plate  302  on the insulating plate  301 . As a result, a portion of the conductor band  200  between the edge portions  312  and  313  is sandwiched between the insulating plates  301  and  302 . Then, as shown in  FIG. 11D , the manufacturer folds the conductor band  200  along the edge portion  313  so as to form a folded portion  252 . As a result, around the folded portion  252 , a section of the second band surface  220  positioned between the edge portions  312  and  313  faces the subsequent section of the second band surface  220 . On the other hand, as shown in  FIG. 11D , the first band surface  210  appears on the insulating plate  302  such that it extends from the edge portion  313  in the Y-axis negative direction. The folded portion  252  corresponds to the second folded part  242  discussed with reference to  FIG. 2A . 
     In  FIG. 11C , a portion of the conductor band  200  sandwiched between the insulating plates  301  and  302  is an example of “a second band portion” in the fifth embodiment. In  FIG. 11D , a portion of the conductor band  200  positioned in front of the insulating plate  302  is an example of “a second remaining portion” in the fifth embodiment. The insulating plate  302  in  FIGS. 11C and 11D  is an example of “a second insulating plate” of the fifth embodiment. 
     After forming the folded portion  252 , as shown in  FIG. 11E , the manufacturer superposes the insulating plate  303  on the insulating plate  302 . As a result, a portion of the conductor band  200  between the edge portions  313  and  314  is sandwiched between the insulating plates  302  and  303 . Then, as shown in  FIG. 11F , the manufacturer folds the conductor band  200  along the edge portion  314  so as to form a folded portion  253 . As a result, around the folded portion  253 , a section of the first band surface  210  positioned between the edge portions  313  and  314  faces the subsequent section of the first band surface  210 . On the other hand, as shown in  FIG. 11F , the second band surface  220  appears on the insulating plate  303  such that it extends from the edge portion  314  in the X-axis negative direction. The folded portion  253  corresponds to the first folded part  241  discussed with reference to  FIG. 2A . 
     In  FIG. 11E , a portion of the conductor band  200  sandwiched between the insulating plates  302  and  303  is an example of “a third band portion” in the fifth embodiment. In  FIG. 11F , a portion of the conductor band  200  positioned in front of the insulating plate  303  is an example of “a third remaining portion” in the fifth embodiment. The insulating plate  303  in  FIGS. 11E and 11F  is an example of “a third insulating plate” of the fifth embodiment. 
     After forming the folded portion  253 , as shown in  FIG. 11G , the manufacturer superposes the insulating plate  304  on the insulating plate  303 . As a result, a portion of the conductor band  200  between the edge portions  314  and  315  is sandwiched between the insulating plates  303  and  304 . Then, as shown in  FIG. 11H , the manufacturer folds the conductor band  200  along the edge portion  315  so as to form a folded portion  254 . As a result, around the folded portion  254 , a section of the second band surface  220  formed between the edge portions  314  and  315  faces a section of the second band surface  220  in a range from the edge portion  315  to the end portion  202 . On the other hand, as shown in  FIG. 11H , the first band surface  210  appears on the insulating plate  304  such that it extends from the edge portion  315  to the end portion  202  in the Y-axis positive direction. The folded portion  254  corresponds to the second folded part  242  discussed with reference to  FIG. 2A . 
     In  FIG. 11G , a portion of the conductor band  200  sandwiched between the insulating plates  303  and  304  is an example of “a fourth band portion” in the fifth embodiment. In  FIG. 11H , a portion of the conductor band  200  positioned in front of the insulating plate  304  is an example of “a fourth remaining portion” or “a fifth band portion” in the fifth embodiment. The insulating plate  304  in  FIGS. 11G and 11H  is an example of “a fourth insulating plate” of the fifth embodiment. 
     Sixth Embodiment 
     In the fifth embodiment, four insulating plates are used for forming one turn section. Alternatively, a single insulating plate may be used for forming one turn section. In a sixth embodiment, a manufacturing method for a coil structure by forming a turn section by using a single insulating plate will be discussed. 
       FIGS. 12A through 12E  are schematic views illustrating steps for folding a conductor band  200  by using an insulating plate  301 . An example of the manufacturing method for a coil structure  100 C will be discussed below with reference to  FIGS. 1 and 12A through 12E . Elements having the same functions as those of the fifth embodiment are designated by like reference numerals, and thus, an explanation thereof will be omitted. 
     In step S 110  of  FIG. 1 , a manufacturer prepares a conductor band  200  and an insulating plate  301 . 
       FIGS. 12A through 12E  show XY coordinates. The conductor band  200  is sequentially folded along edge portions  312  through  315  of the insulating plate  301 . In the process in which the conductor band  200  is being folded, the conductor band  200  is constituted by a portion extending in the X-axis direction and a portion extending in the Y-axis direction. 
     The first band surface  210  of the conductor band  200  extending in the Y-axis positive direction is shown in  FIG. 12A . As shown in  FIG. 12A , a manufacturer superposes the insulating plate  301  on a start portion  201  of the conductor band  200 . Then, as shown in  FIG. 12B , the manufacturer folds the conductor band  200  along the edge portion  312  so as to form a folded portion  251 . As a result, around the edge portion  312 , a section of the first band surface  210  in a range from the start portion  201  to the edge portion  312  faces the remaining section of the first band surface  210 . On the other hand, as shown in  FIG. 12B , the second band surface  220  appears on the insulating plate  301  such that it extends from the edge portion  312  in the X-axis positive direction. 
     In  FIG. 12A , a portion in which the insulating plate  301  and the conductor band  200  are superposed is an example of “a first band portion” in the sixth embodiment. In  FIG. 12B , a portion of the conductor band  200  positioned in front of the insulating plate  301  is an example of “a first remaining portion” in the sixth embodiment. 
     After forming the folded portion  251 , as shown in  FIG. 12C , the manufacturer folds the conductor band  200  along the edge portion  313  so as to form a folded portion  252 C. As a result, around the folded portion  252 C, a section of the first band surface  210  positioned between the edge portions  312  and  313  faces the subsequent section of the first band surface  210 . In  FIG. 12C , the first band surface  210  appears behind the insulating plate  301  such that it extends from the edge portion  313  in the Y-axis negative direction. 
     In  FIG. 12C , a portion of the conductor band  200  positioned in front of the insulating plate  301  is an example of “a second band portion” in the sixth embodiment. In  FIG. 12C , a portion of the conductor band  200  positioned behind the insulating plate  301  and extending from the folded portion  252 C is an example of “a second remaining portion” in the sixth embodiment. 
     After forming the folded portion  252 C, as shown in  FIG. 12D , the manufacturer folds the conductor band  200  along the edge portion  314  so as to form a folded portion  253 C. As a result, around the folded portion  253 C, a section of the first band surface  210  formed between the edge portions  313  and  314  faces the subsequent section of the first band surface  210 . In  FIG. 12D , the second band surface  220  appears on the insulating plate  301  such that it extends from the edge portion  314  in the X-axis negative direction. 
     In  FIG. 12D , a portion of the conductor band  200  positioned behind the insulating plate  301  and extending between the folded portions  252 C and  253 C is an example of “a third band portion” in the sixth embodiment. In  FIG. 12D , a portion of the conductor band  200  positioned in front of the insulating plate  301  and extending from the folded portion  253 C in the X-axis negative direction is an example of “a third remaining portion” in the sixth embodiment. 
     After forming the folded portion  253 C, as shown in  FIG. 12E , the manufacturer folds the conductor band  200  along the edge portion  315  so as to form a folded portion  254 C. As a result, around the folded portion  254 C, a section of the first band surface  210  positioned between the edge portions  314  and  315  faces a section of the first band surface  210  in a range from the edge portion  315  to the end portion  202 . The end portion  202  is located close to the start portion  201 . As a result of folding the conductor band  200 , one turn section is formed. In this manner, the coil structure  100 C including one turn section is formed. 
     In  FIG. 12E , a portion of the conductor band  200  positioned in front of the insulating plate  301  and extending between the folded portions  253 C and  254 C is an example of “a fourth band portion” in the sixth embodiment. In  FIG. 12E , a portion of the conductor band  200  positioned behind the insulating plate  301  and extending from the folded portion  254 C is an example of “a fourth remaining portion” or “a fifth band portion” in the sixth embodiment. In  FIG. 12E , the folded portions  251 ,  252 C,  253 C, and  254 C are examples of “a plurality of folded parts” in the sixth embodiment. At each of the folded portions  251 ,  252 C,  253 C, and  254 C, part of the first band surface  210  is folded inwardly. 
     The coil structure  100 C may be used singly. Alternatively, the manufacturer may repeat the folding steps shown in  FIGS. 12A through 12E  so as to prepare a plurality of coil structures  100 C. The manufacturer may align the plurality of coil structures  100 C and may also interpose an insulating member between the coil structures  100 C. 
     Seventh Embodiment 
     A coil structure is applicable to various devices. If a device into which a coil structure is integrated is designed to be small, the coil structure may be disposed near another component within the device. In this case, in terms of the safety and the reliability of the device, a long creepage distance may be required between the coil structure and another component. In a seventh embodiment, an insulating plate which makes it possible to provide a long creepage distance between a coil structure and another component will be discussed. The insulating plate in the seventh embodiment may be used instead of the insulating plates used in the second through fourth embodiments. 
       FIG. 13A  is a schematic perspective view illustrating an example of an insulating plate  300 D.  FIG. 13B  is a schematic plan view illustrating the insulating plate  300 D.  FIG. 13C  is a schematic sectional view taken along line XIIIC-XIIIC of  FIG. 13B . The insulating plate  300 D will be discussed below with reference to  FIGS. 2A and 13A through 13C . 
     The insulating plate  300 D includes a first surface  331 , a second surface  332  opposite the first surface  331 , an outer periphery  333  which connects an outer contour of the first surface  331  and an outer contour of the second surface  332 , and an inner periphery  334  which defines an axial hole  319 D coaxial with the outer periphery  333 . In the seventh embodiment, the outer periphery  333 , which defines a contour of the insulating plate  300 D, and the axial hole  319 D are, for example, circular. However, the insulating plate  300 D and the axial hole  319 D may be formed in another shape. The contour of the insulating plate  300 D and the axial hole  319 D are not restricted to a circular shape. 
     In the insulating plate  300 D, first through fourth through-holes  341  through  344  are formed. The first through fourth through-holes  341  through  344  are disposed around the axial hole  319 D at substantially regular intervals. 
     If the folding pattern of the conductor band  200  discussed with reference to  FIG. 2A  is used, the conductor band  200  passes through one of the first through fourth through-holes  341  through  344 . If the folding pattern discussed in the sixth embodiment is used, the conductor band  200  sequentially passes through the first through fourth through-holes  341  through  344 . In the present disclosure, one of the first through fourth through-holes  341  through  344  is an example of a “through-hole” of the present disclosure. 
     In the example shown in  FIGS. 13A and 13B , the insulating plate  300 D has four through-holes. However, the number, configuration, and arrangement of the through-holes may be determined suitably in accordance with the folding pattern of the conductor band  200 . The number, configuration, and arrangement of the through-holes are not restricted. 
     The insulating plate  300 D includes edge portions  311 D through  314 D used for folding the conductor band  200 . The edge portions  311 D through  314 D partially form the contours of the first through fourth through-holes  341  through  344 , respectively. 
     In other words, the edge portion  311 D is part of the inner peripheral surface which defines the first through-hole  341 , the edge portion  312 D is part of the inner peripheral surface which defines the second through-hole  342 , the edge portion  313 D is part of the inner peripheral surface which defines the third through-hole  343 , and the edge portion  314 D is part of the inner peripheral surface which defines the fourth through-hole  344 . 
     An outer area of the insulating plate  300 D, positioned farther away from the coil axis CA than the first through fourth through-holes  341  through  344 , can contribute to increasing the creepage distance between a coil structure and another component disposed close to the coil structure. 
     Eighth Embodiment 
     If a coil structure is formed by winding a conductor band around a plurality of insulating plates, the conductor band passes through a pair of insulating plates. Accordingly, these insulating plates are separated from each other by the thickness of the conductor band, thereby increasing the dimension of the coil structure in a direction along the coil axis. In an eighth embodiment, an insulating plate which makes it possible to reduce the dimension of a coil structure in a direction along the coil axis will be discussed. The insulating plate in the eighth embodiment may be used instead of the various insulating plates discussed in the above-described embodiments. 
       FIG. 14A  is a schematic perspective view illustrating an example of an insulating plate  300 E.  FIG. 14B  is a schematic plan view illustrating the insulating plate  300 E.  FIG. 14C  is a schematic sectional view taken along line XIVC-XIVC of  FIG. 14B . The insulating plate  300 E will be discussed below with reference to  FIGS. 2A and 14A through 14C . Elements having the same functions as those of the seventh embodiment are designated by like reference numerals, and thus, an explanation thereof will be omitted. 
     As in the seventh embodiment, the insulating plate  300 E includes a second surface  332 , an outer periphery  333 , and an inner periphery  334 . In the insulating plate  300 E, the axial hole  319 D and first through fourth through-holes  341  through  344  are formed. 
     The insulating plate  300 E also includes a first surface  331 E opposite the second surface  332 . In the first surface  331 E, first and second grooves  351  and  352  are formed. For example, in the first groove  351 , a band portion of the conductor band  200  extending between the first and second through-holes  341  and  342  is held, and in the second groove  352 , a band portion of the conductor band  200  extending between the third and fourth through-holes  343  and  344  is held. 
     If the folding pattern of the conductor band  200  discussed with reference to  FIG. 2A  is employed, one of the band portions of the conductor band  200  extends along one of the first and second grooves  351  and  352 . If the folding pattern discussed in the sixth embodiment is employed, band portions of the conductor band  200  are held in both of the first and second grooves  351  and  352 . 
       FIG. 15  is an exploded sectional view illustrating a coil structure  100 E formed by using the insulating plate  300 E. The coil structure  100 E will be discussed below with reference to  FIGS. 2A and 15 . 
     The coil structure  100 E includes two insulating plates  300 E and a conductor band  200 . One of the two insulating plates  300 E will be referred to as “a first insulating plate  301 E”, and the other one of the insulating plates  300 E will be referred to as “a second insulating plate  302 E”. The first and second insulating plates  301 E and  302 E are aligned along the coil axis CA. 
     The second surface  332  of the first insulating plate  301 E opposes the first surface  331  of the second insulating plate  302 E. The second surface  332  of the first insulating plate  301 E is an example of “a first opposing surface” in the eighth embodiment, and a first surface  331 E of the second insulating plate  302 E is an example of “a second opposing surface” in the eighth embodiment. 
     As shown in  FIG. 2A , the conductor band  200  includes a straight band portion extending between the first and second folding portions  241  and  242 .  FIG. 15  shows a cross section of such a band portion of the conductor band  200 . 
     The band portion of the conductor band  200  is held within the first groove  351  or the second groove  352 . Accordingly, the second surface  332  of the first insulating plate  301 E is in close contact with the first surface  331 E of the second insulating plate  302 E. Since the second surface  332  of the first insulating plate  301 E closes the first and second grooves  351  and  352 , the band portion of the conductor band  200  is suitably held within the first groove  351  or the second groove  352 . The space within the first groove  351  or the second groove  352  closed by the second surface  332  of the first insulating plate  301 E is an example of “a holding section” of the present disclosure. 
     In the eighth embodiment, the first and second grooves  351  and  352  are formed in the first surface  331 E. Alternatively, grooves for holding conductor bands therein may be formed in both of the first and second surfaces  331 E and  332 . 
     Ninth Embodiment 
     In the second through eighth embodiments, four folded portions are formed in one turn section. If many folded portions are formed in one turn section, the effect of providing twisted wire is noticeably exhibited. The present inventors have found that, if five or more folded portions are formed in one turn section, power loss in a coil structure may be significantly reduced due to the effect of providing twisted wire. In a ninth embodiment, a conductor band including six folded portions in one turn section will be described. 
       FIG. 16A  is a schematic perspective view illustrating an example of the conductor band  200 .  FIG. 16B  is a schematic plan view illustrating the conductor band  200 . The conductor band  200  of the ninth embodiment will be described below with reference to  FIGS. 16A and 16B . Elements having the same functions as those of the second or fifth embodiment are designated by like reference numerals, and thus, an explanation thereof will be omitted. 
     A manufacturer may repeatedly fold the conductor band  200  so as to form six folded portions  240 F in one turn section. The six folded portions  240 F may be constituted by three first folded parts  241  and three second folded parts  242 . The first and second folded parts  241  and  242  may be alternately formed in a range from the start portion  201  to the end portion  202 . 
       FIG. 17A  is a schematic perspective view illustrating an example of an insulating plate  300 F which is combined with the folded portions  240 F.  FIG. 17B  is a schematic plan view illustrating the insulating plate  300 F. The insulating plate  300 F will be discussed below with reference to  FIGS. 16A through 17B . 
     The insulating plate  300 F includes a substantially dodecagonal base portion  310 F and six protruding portions  320 F protruding from the base portion  310 F. The base portion  310 F includes six outer peripheral edges  311 F. The protruding portions  320 F and the outer peripheral edges  311 F are alternately disposed. One of the six outer peripheral edges  311 F abuts along one of the folded portions  240 F shown in  FIGS. 16A and 16B . Accordingly, the outer peripheral edge  311 F can define the folding angle of the folded portion  240 F. A pair of protruding portions  320 F, between which a folded portion  240 F is disposed, has surfaces opposing the side surfaces  231  and  232  of the conductor band  200  of the folded portion  240 F. Accordingly, the protruding portions  320 F can stably maintain the positions of the folded portions  240 F. One of the outer peripheral edges  311 F is an example of “a first edge portion” of the present disclosure. 
       FIG. 18A  is a schematic perspective view illustrating a coil structure  100 F.  FIG. 18B  is a schematic plan view illustrating the coil structure  100 F. The coil structure  100 F will be described below with reference to  FIGS. 18A and 18B . 
     The coil structure  100 F includes a conductor band  200  and six insulating plates  300 F. The six insulating plates  300 F are aligned along the coil axis CA. One of the outer peripheral edges  311 F of each of the six insulating plates  300 F is used for forming one of the six folding sections  240 F. 
     Tenth Embodiment 
     A coil structure is applicable to various devices. If a device into which a coil structure is integrated is designed to be small, the coil structure may be disposed near another component within the device. In this case, in terms of the safety and the reliability of the device, a long creepage distance may be required between the coil structure and another component. In a tenth embodiment, an insulating plate which makes it possible to provide a long creepage distance between a coil structure and another component will be discussed. The insulating plate in the tenth embodiment may be used instead of the insulating plate used in the ninth embodiment. 
       FIG. 19  is a schematic perspective view illustrating an example of an insulating plate  300 G. The insulating plate  300 G will be discussed below with reference to  FIGS. 16A and 19 . Elements having the same functions as those of the seventh embodiment are designated by like reference numerals, and thus, an explanation thereof will be omitted. 
     As in the seventh embodiment, the insulating plate  300 G includes a first surface  331 , a second surface  332  opposite the first surface  331 , an outer periphery  333 , and an inner periphery  334 . In the insulating plate  300 G, an axial hole  319 D is formed. 
     In the insulating plate  300 G, first through sixth through-holes  341 G through  346 G are formed. The first through sixth through-holes  341 G through  346 G are disposed around the axial hole  319 D at substantially regular intervals. 
     The conductor band  200  discussed with reference to  FIG. 16A  passes through one of the first through sixth through-holes  341 G through  346 G. One of the first through sixth through-holes  341 G through  346 G is an example of a “through-hole” of the present disclosure. 
     The insulating plate  300 G includes edge portions  311 G through  316 G used for folding the conductor band  200 . The edge portions  311 G through  316 G partially form the contours of the first through sixth through-holes  341 G through  346 G, respectively. 
     An outer area of the insulating plate  300 G, positioned farther away from the coil axis CA than the first through sixth through-holes  341 G through  346 G, can contribute to increasing the creepage distance between a coil structure and another component disposed close to the coil structure. 
     Eleventh Embodiment 
     The coil structures discussed in the second through tenth embodiments each include a single conductor band. Alternatively, a coil structure may include a plurality of conductor bands. If multiple conductor bands are used, a user can easily supply high electrical energy to a coil structure. Thus, in the case of using multiple conductor bands, individual conductor bands may be thin. If thin conductor bands are used, electrical resistance is significantly reduced due to the effect of providing twisted wire. The user may supply electrical energy to one of the plurality of conductor bands. If, as a result of supplying electrical energy to one of the conductor bands, an induced current is generated in another conductor band, the coil structure may be used as a transformer. In an eleventh embodiment, a coil structure including two conductor bands will be described. 
       FIG. 20  is a schematic perspective view illustrating an example of a folding pattern of a plurality of conductor bands. A folding pattern of a plurality of conductor bands will be discussed below with reference to  FIG. 20 . Elements having the same functions as those of the fifth embodiment are designated by like reference numerals, and thus, an explanation thereof will be omitted. 
       FIG. 20  includes a first conductor band  410  and a second conductor band  420 . The first conductor band  410  has one turn section which turns around the coil axis CA through one revolution. The second conductor band  410  also has one turn section which turns around the coil axis CA through one revolution. The first and second conductor bands  410  and  420  may each have multiple turn sections. The number of turn sections is not restricted. 
     The first conductor band  410  includes four folded portions  411  within one turn section. The four folded portions  411  are constituted by two first folded parts  241  and two second folded parts  242 . The first folded parts  241  and the second folded parts  242  are alternately formed. 
     The second conductor band  420  includes four folded portions  421  within one turn section. The four folded portions  421  are constituted by two first folded parts  241  and two second folded parts  242 . The first folded parts  241  and the second folded parts  242  are alternately formed. 
       FIGS. 21A through 21H  schematically illustrate the first and second conductor bands  410  and  420  which are folded by using insulating plates  301  through  304 . A manufacturing method for a coil structure  100 H will be described below with reference to  FIGS. 21A through 21H . 
     The first and second conductor bands  410  and  420  are sequentially folded along edge portions  312  through  315 . In the process in which the first and second conductor bands  410  and  420  are being folded, the first and second conductor bands  410  and  420  are each constituted by a portion extending in the X-axis direction and a portion extending in the Y-axis direction. 
     The first conductor band  410  has a start portion  412  and an end portion  413  opposite to the start portion  412 . The first conductor band  410  has one turn section between the start portion  412  and the end portion  413 . 
     The second conductor band  420  has a start portion  422  and an end portion  423  opposite to the start portion  422 . The second conductor band  420  has one turn section between the start portion  422  and the end portion  423 . 
     As shown in  FIG. 21A , a manufacturer disposes the second conductor band  420  next to the first conductor band  410 . In  FIG. 21A , both of the first and second conductor bands  410  and  420  extend in the Y-axis positive direction. The manufacturer then superposes an insulating plate  301  on the start portions  412  and  422 . Then, as shown in  FIG. 21B , the manufacturer folds the first and second conductor bands  410  and  420  along the edge portion  312 . As a result, a folded portion  411  of the first conductor band  410  is formed, and a folded portion  421  of the second conductor band  420  is formed. 
     After forming the folded portions  411  and  421 , as shown in  FIG. 21C , the manufacturer superposes an insulating plate  302  on the insulating plate  301 . As a result, the first and second conductor bands  410  and  420  positioned between the edge portions  312  and  313  are sandwiched between the insulating plates  301  and  302 . Then, as shown in  FIG. 21D , the manufacturer folds the first and second conductor bands  410  and  420  along the edge portion  313 . As a result, a folded portion  411  of the first conductor band  410  is formed, and a folded portion  421  of the second conductor band  420  is formed. 
     After forming the folded portions  411  and  421 , as shown in  FIG. 21E , the manufacturer superposes an insulating plate  303  on the insulating plate  302 . As a result, the first and second conductor bands  410  and  420  positioned between the edge portions  313  and  314  are sandwiched between the insulating plates  302  and  303 . Then, as shown in  FIG. 21F , the manufacturer folds the first and second conductor bands  410  and  420  along the edge portion  314 . As a result, a folded portion  411  of the first conductor band  410  is formed, and a folded portion  421  of the second conductor band  420  is formed. 
     After forming the folded portions  411  and  421 , as shown in  FIG. 21G , the manufacturer superposes an insulating plate  304  on the insulating plate  303 . As a result, the first and second conductor bands  410  and  420  positioned between the edge portions  314  and  315  are sandwiched between the insulating plates  303  and  304 . Then, as shown in  FIG. 21H , the manufacturer folds the first and second conductor bands  410  and  420  along the edge portion  315 . As a result, a folded portion  411  of the first conductor band  410  is formed, and a folded portion  421  of the second conductor band  420  is formed. 
     The edge portions  312  through  315  abut along the four respective folded portions  411 . The edge portions  312  through  315  also abut along the four respective folded portions  421 . The four folded portions  411  are examples of “a first plurality of folded portions” in the eleventh embodiment. The four folded portions  421  are examples of “a second plurality of folded portions” in the eleventh embodiment. One of the edge portions  312  through  315  is an example of “a first edge portion” in the eleventh embodiment. 
     Twelfth Embodiment 
     In the eleventh embodiment, each of the insulating plates has a plurality of edge portions. The first and second conductor bands  410  and  420  are folded by using the common edge portions. Alternatively, a second conductor band may be folded by using an edge portion different from an edge portion used for folding a first conductor band. In this case, the second conductor band defines a spiral path different from that of the first conductor band. Accordingly, the first and second conductor bands may be constituted by thick metallic bands. In a twelfth embodiment, a coil structure including first and second conductor bands that define different spiral paths will be described. If a user supplies electrical energy to one of the first and second conductor bands, an induced current is generated in the other one of the first and second conductor bands, and thus, the coil structure may be used as a transformer. 
       FIG. 22  is a schematic perspective view illustrating an example of a coil structure  100 I.  FIG. 23  is a schematic perspective view illustrating an example of a folding pattern of a plurality of conductor bands. A folding pattern of a plurality of conductor bands will be discussed below with reference to  FIGS. 22 and 23 . Elements having the same functions as those of the eleventh embodiment are designated by like reference numerals, and thus, an explanation thereof will be omitted. 
     As in the eleventh embodiment, the coil structure  100 I includes insulating plates  301  through  304 . The coil structure  100 I includes a first conductor band  510  and a second conductor band  520 . 
     The first conductor band  510  has a start portion  512  and an end portion  513  opposite to the start portion  512 . The first conductor band  510  has one turn section between the start portion  512  and the end portion  513 . The first conductor band  510  may have multiple turn sections. The number of turn sections is not restricted. 
     The second conductor band  520  has a start portion  522  and an end portion  523  opposite to the start portion  522 . The second conductor band  520  has one turn section between the start portion  522  and the end portion  523 . The second conductor band  520  may have multiple turn sections. The number of turn sections is not restricted. 
     The start portion  522  of the second conductor band  520  is disposed symmetrically to the start portion  512  of the first conductor band  510  about the coil axis CA, for example. In this case, the end portion  523  of the second conductor band  520  is disposed symmetrically to the end portion  513  of the first conductor band  510  about the coil axis CA. Accordingly, the turning phase of the second conductor band  520  around the coil axis CA is out of phase from that of the first conductor band  510  by 180°. The phase difference between the first and second conductor bands  510  and  520  is not restricted to 180°. 
     The first conductor band  510  includes a folded portion  511  folded by using the edge portion  312  of the insulating plate  301 . The second conductor band  520  includes a folded portion  521  folded by using the edge portion  314  of the insulating plate  301 . The edge portion  312  abuts along the folded portion  511  of the first conductor band  510 , while the edge portion  314  opposite the edge portion  312  abuts along the folded portion  521  of the second conductor band  520 . 
     The first conductor band  510  includes a folded portion  511  folded by using the edge portion  313  of the insulating plate  302 . The second conductor band  520  includes a folded portion  521  folded by using the edge portion  315  of the insulating plate  302 . The edge portion  313  abuts along the folded portion  511  of the first conductor band  510 , while the edge portion  315  opposite the edge portion  313  abuts along the folded portion  521  of the second conductor band  520 . 
     The first conductor band  510  includes a folded portion  511  folded by using the edge portion  314  of the insulating plate  303 . The second conductor band  520  includes a folded portion  521  folded by using the edge portion  312  of the insulating plate  303 . The edge portion  314  abuts along the folded portion  511  of the first conductor band  510 , while the edge portion  312  opposite the edge portion  314  abuts along the folded portion  521  of the second conductor band  520 . 
     The first conductor band  510  includes a folded portion  511  folded by using the edge portion  315  of the insulating plate  304 . The second conductor band  520  includes a folded portion  521  folded by using the edge portion  313  of the insulating plate  304 . The edge portion  315  abuts along the folded portion  511  of the first conductor band  510 , while the edge portion  313  opposite the edge portion  315  abuts along the folded portion  521  of the second conductor band  520 . 
     The four folded portions  511  are examples of “a first plurality of folded portions” in the twelfth embodiment. The four folded portions  521  are examples of “a second plurality of folded portions” in the twelfth embodiment. When the edge portion  312  is an example of “a first edge portion”, the edge portion  314  is an example of “a different edge portion” in the twelfth embodiment. When the edge portion  313  is an example of “a first edge portion”, the edge portion  315  is an example of “a different edge portion” in the twelfth embodiment. When the edge portion  314  is an example of “a first edge portion”, the edge portion  312  is an example of “a different edge portion” in the twelfth embodiment. When the edge portion  315  is an example of “a first edge portion”, the edge portion  313  is an example of “a different edge portion” in the twelfth embodiment. 
     Thirteenth Embodiment 
     The coil structures formed based on the above-described various embodiments may be integrated, as a transformer, such as a voltage converter or a shift converter, into a power converter for converting an alternating current into a direct current. In this case, a power converter may be integrated into a charger for storing electrical energy therein. In a thirteenth embodiment, a power converter including one or more of the coil structures formed based on the above-described various embodiments will be described. 
       FIG. 24  is a schematic block diagram illustrating an example of a power converter  600 . The power converter  600  will be described below with reference to  FIG. 24 . 
     The power converter  600  includes a primary circuit  610 , a secondary circuit  620 , and a coil structure  630 . The primary circuit  610  includes a switching element  611 . For stabilizing the voltage of the secondary circuit  620 , ON/OFF timings of the switching element  611  may be adjusted. The primary circuit  610  is an example of “a switching circuit” of the present disclosure. 
     The coil structure  630  may be formed on the basis of one of the above-described various embodiments. Alternatively, the coil structure  630  may be formed by a combination of the above-described various embodiments. 
     The coil structure  630  may function as a transformer for insulating the secondary circuit  620  from the primary circuit  610 . 
     The power converter  600  may convert an alternating current input into the primary circuit  610  into a direct current. In this case, the power converter  600  may be integrated into a charger. 
     The present disclosure is suitably used for various devices utilizing electromagnetic induction. 
     While the present disclosure has been described with respect to exemplary embodiments thereof, it will be apparent to those skilled in the art that the disclosure may be modified in numerous ways and may assume many embodiments other than those specifically described above. Accordingly, it is intended by the appended claims to cover all modifications of the disclosure that fall within the true spirit and scope of the disclosure.