Transformer

CROSS-REFERENCE TO RELATED APPLICATIONS

0001This application is based on and claims priority from Japanese Patent Applications No. 2011-72154 filed on Mar. 29, 2011 and No. 2011-272495 filed on Dec. 13, 2011, the contents of which are hereby incorporated by reference in their entireties into this application.

BACKGROUND

00021. Technical Field

0003The present invention relates to transformers which include a plurality of coils that are electrically insulated from each other and stacked in a common winding axial direction thereof.

00042. Description of the Related Art

0005There are known transformers which are used in, for example, DC-DC converters. Those transformers include, as shown in <figref idref="DRAWINGS">FIG. 30</figref>, a high voltage-side coil <b>91</b> and a pair of low voltage-side coils <b>92</b> that are electrically insulated from each other and stacked in a common winding axial direction thereof (i.e., the direction of the winding axes of the coils <b>91</b> and <b>92</b> which coincide with each other). More specifically, the coils <b>91</b> and <b>92</b> are stacked so that the high voltage-side coil <b>91</b> is interposed between the low voltage-side coils <b>92</b> in the winding axial direction. Further, the coils <b>91</b> and <b>92</b> are together sandwiched by a pair of core pieces <b>93</b> in the winding axial direction. With the core pieces <b>93</b>, magnetic paths can be formed on both the radially inside and radially outside of the coils <b>91</b> and <b>92</b>.

0006Moreover, electrical insulation between the high voltage-side coil <b>91</b>, the low voltage-side coils <b>92</b> and the core pieces <b>93</b> is secured by interposing therebetween bobbins <b>94</b> that are made of an electrically-insulative material. However, with the bobbins <b>94</b>, both the size and parts count of the transformer <b>9</b> are increased and the assembly process of the transformer <b>9</b> is complicated.

0007To solve the above problem, Japanese Patent Application Publication No. 2004-303857 discloses a technique, according to which the high voltage-side coil <b>91</b> is comprised of a substrate that has coil patterns formed on both the major surfaces thereof and insulating layers <b>911</b> that cover the coil patterns. Consequently, the high voltage-side coil <b>91</b> is electrically insulated from the low voltage-side coils <b>92</b> without interposing the bobbins <b>94</b> between the high voltage-side coil <b>91</b> and the low voltage-side coils <b>92</b>.

0008However, with the above technique, it is still necessary to interpose the bobbins <b>94</b> between the low voltage-side coils <b>92</b> and the core pieces <b>93</b> for securing the electrical insulation therebetween. Consequently, it is difficult to minimize both the size and parts count of the transformer <b>9</b> and simplify the assembly process of the transformer <b>9</b>.

SUMMARY

0009According to an exemplary embodiment, a transformer is provided which includes a pair of first coils and at least one second coil. The first and second coils are stacked so that the at least one second coil is interposed between the first coils in a common winding axial direction of the first and second coils. Each of the first coils is covered by insulating films and integrated with the insulating films into an integrated body, so that the first coils are electrically insulated from the at least one second coil.

0010With the above configuration, electrical insulation between the first coils and the at least one second coil is secured by means of the thin insulating films that cover the first coils. Consequently, it becomes possible to minimize the thickness of the transformer in the winding axial direction while securing the electrical insulation between the first coils and the at least one second coil. Moreover, since each of the first coils is integrated with the insulating films into one integrated body, the parts count of the transformer is prevented from increasing and the assembly process of the transformer is prevented from becoming complicated.

0011Accordingly, with the above configuration, it is possible to minimize both the size and parts count of the transformer and simplify the assembly process of the transformer while securing the electrical insulation between the first coils and the at least one second coil.

0012In a further implementation, the transformer further includes a core that is comprised of a pair of core pieces. The integrated bodies, each of which is comprised of one of the first coils and the insulating films covering the one of the first coils, and the at least one second coil are together interposed between and thereby covered by the pair of core pieces in the winding axial direction.

0013In this case, since the at least one second coil is interposed between the first coils in the winding axial direction, the at least one second coil is prevented from making contact with the core pieces that are arranged outside of the first coils in the winding axial direction. Consequently, electrical insulation between the at least one second coil and the core pieces is secured without employing any additional insulating means (e.g., bobbins). Moreover, electrical insulation between the first coils and the core pieces is also secured by means of the thin insulating films that cover the first coils.

0014In still further implementations, each of the first coils is comprised of a plurality of coil segments that are stacked in the winding axial direction. Between each adjacent pair of the coil segments, there is interposed an insulating film so as to electrically insulate the coil segments from each other.

0015The integrated bodies, each of which is comprised of one of the first coils and the insulating films covering the one of the first coils, are substantially annular-shaped. The at least one second coil is also substantially annular-shaped. The radially inner periphery of the at least one second coil is positioned radially outside of the radially inner peripheries of the insulating films of the integrated bodies, and the radially outer periphery of the at least one second coil is positioned radially inside of the radially outer peripheries of the insulating films.

0016The at least one second coil is bonded by an adhesive to a corresponding one of the integrated bodies.

0017The integrated bodies are formed of a coil sheet. In the coil sheet, the integrated bodies are connected with each other via a connecting portion. The coil sheet is folded at the connecting portion so that the integrated bodies are superposed in the winding axial direction. The connecting portion of the coil sheet includes therein a connecting electric conductor that connects the first coils included in the respective integrated bodies.

0018Further, in the coil sheet, there are provided two coil terminals that protrude respectively from the integrated bodies in a direction perpendicular to both the winding axial direction and an extending direction of the connecting portion of the coil sheet.

0019Each of the core pieces of the core has a center portion that extends in the winding axial direction. The center portions of the core pieces are inserted in a space formed radially inside of the integrated bodies and the at least one second coil. The insulating films of the integrated bodies have extensions that extend in the winding axial direction along the outer surfaces of the center portions of the core pieces, so as to be radially interposed between the outer surfaces of the center portions of the core pieces and the radially inner surface of the at least one second coil.

0020Each of the first coils is comprised of a large-linewidth coil segment and a small-linewidth coil segment that are stacked in the winding axial direction. The at least one second coil is directly thermally connected to a heat sink. The first coils and the at least one second coil are stacked so that the large-linewidth coil segments of the first coils face the at least one second coil.

BRIEF DESCRIPTION OF THE DRAWINGS

0021The present invention will be understood more fully from the detailed description given hereinafter and from the accompanying drawings of exemplary embodiments, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only.

0022In the accompanying drawings:

0023<figref idref="DRAWINGS">FIG. 1</figref> is a cross-sectional view illustrating the overall configuration of a transformer according to a first embodiment;

0024<figref idref="DRAWINGS">FIG. 2</figref> is a cross-sectional view of a stacked body of the transformer;

0025<figref idref="DRAWINGS">FIG. 3</figref> is a cross-sectional view of part of an integrated body of a first coil and insulating films, the integrated body being included in the stacked body;

0026<figref idref="DRAWINGS">FIG. 4</figref> is an exploded perspective view of the transformer;

0027<figref idref="DRAWINGS">FIG. 5</figref> is a plan view of a coil sheet, of which a pair of the integrated bodies is formed, before being folded;

0028<figref idref="DRAWINGS">FIG. 6</figref> is a cross-sectional view taken along the line A-A in <figref idref="DRAWINGS">FIG. 5</figref>;

0029<figref idref="DRAWINGS">FIG. 7</figref> is a plan view illustrating a pair of large-linewidth electric conductor plates included in the coil sheet before being folded;

0030<figref idref="DRAWINGS">FIG. 8</figref> is a plan view illustrating a pair of small-linewidth electric conductor plates included in the coil sheet before being folded;

0031<figref idref="DRAWINGS">FIG. 9</figref> is a plan view of the coil sheet which is folded to have the pair of the integrated bodies superposed;

0032<figref idref="DRAWINGS">FIG. 10</figref> is a cross-sectional view taken along the line B-B in <figref idref="DRAWINGS">FIG. 9</figref>;

0033<figref idref="DRAWINGS">FIG. 11</figref> is a plan view illustrating the transformer which is mounted on a heat sink;

0034<figref idref="DRAWINGS">FIG. 12</figref> is a cross-sectional view illustrating connecting terminals of a pair of second coils of the transformer, the connecting terminals being fixed to a terminal block of the heat sink;

0035<figref idref="DRAWINGS">FIG. 13</figref> is a cross-sectional view of a stacked body according to a second embodiment;

0036<figref idref="DRAWINGS">FIG. 14</figref> is a cross-sectional view of a coil sheet according to the second embodiment before being folded, wherein a pair of second coils is bonded to the coil sheet;

0037<figref idref="DRAWINGS">FIG. 15</figref> is a cross-sectional view illustrating the overall configuration of a transformer according to a third embodiment;

0038<figref idref="DRAWINGS">FIG. 16</figref> is a cross-sectional view of a stacked body of the transformer according to the third embodiment;

0039<figref idref="DRAWINGS">FIG. 17</figref> is a plan view of a coil sheet according to the third embodiment before being folded;

0040<figref idref="DRAWINGS">FIG. 18</figref> is a plan view of a coil sheet according to a fourth embodiment before being folded;

0041<figref idref="DRAWINGS">FIG. 19</figref> is a cross-sectional view of a stacked body according to the fourth embodiment;

0042<figref idref="DRAWINGS">FIG. 20</figref> is a plan view of a coil sheet according to a first modification of the fourth embodiment;

0043<figref idref="DRAWINGS">FIG. 21</figref> is a cross-sectional view of a stacked body according to the first modification;

0044<figref idref="DRAWINGS">FIG. 22</figref> is a plan view of a coil sheet according to a second modification of the fourth embodiment;

0045<figref idref="DRAWINGS">FIG. 23</figref> is a cross-sectional view of a stacked body according to the second modification;

0046<figref idref="DRAWINGS">FIG. 24</figref> is a cross-sectional view illustrating a pair of stacked bodies of a transformer according to a fifth embodiment;

0047<figref idref="DRAWINGS">FIG. 25</figref> is a cross-sectional view illustrating the overall configuration of a transformer according to a sixth embodiment;

0048<figref idref="DRAWINGS">FIG. 26</figref> is a plan view of a coil sheet according to a seventh embodiment before being folded;

0049<figref idref="DRAWINGS">FIG. 27</figref> is a plan view of a coil sheet according to an eighth embodiment before being folded;

0050<figref idref="DRAWINGS">FIG. 28</figref> is a plan view of a coil sheet according to a ninth embodiment before being folded;

0051<figref idref="DRAWINGS">FIG. 29</figref> is a plan view of a coil sheet according to a modification of the night embodiment before being folded; and

0052<figref idref="DRAWINGS">FIG. 30</figref> is a cross-sectional view illustrating the overall configuration of a transformer according to the prior art.

DESCRIPTION OF EMBODIMENTS

0053Exemplary embodiments will be described hereinafter with reference to <figref idref="DRAWINGS">FIGS. 1-29</figref>. It should be noted that for the sake of clarity and understanding, identical components having identical functions in different embodiments have been marked, where possible, with the same reference numerals in each of the figures and that for the sake of avoiding redundancy, descriptions of the identical components will not be repeated.

First Embodiment

0054Referring to <figref idref="DRAWINGS">FIGS. 1 and 4</figref>, a transformer <b>1</b> according to the first embodiment includes a pair of first coils <b>10</b> and a pair of second coils <b>20</b>. The first and second coils <b>10</b> and <b>20</b> are electrically insulated from each other and stacked (or superposed) in a common winding axial direction thereof (i.e., the direction of the winding axes of the coils <b>10</b> and <b>20</b> which coincide with each other).

0055Moreover, as shown in <figref idref="DRAWINGS">FIGS. 1 and 2</figref>, each of the first coils <b>10</b> is covered by insulating films <b>11</b> and integrated with the insulating films <b>11</b> into an integrated body <b>100</b>. Accordingly, there are two integrated bodies <b>100</b> included in the transformer <b>1</b>.

0056The first and second coils <b>10</b> and <b>20</b> are stacked so that the pair of second coils <b>20</b> is interposed between the first coils <b>10</b> in the winding axial direction.

0057In the present embodiment, the transformer <b>1</b> is configured as a step-down transformer. The transformer <b>1</b> may be used in, for example, an electric vehicle or a hybrid vehicle to step down (or reduce) voltage for charging a low-voltage power source with electric power supplied by a high-voltage power source. In addition, the first coils <b>10</b> are configured as primary and high voltage-side coils, and the second coils <b>20</b> are configured as secondary and low voltage-side coils.

0058Each of the first and second coils <b>10</b> and <b>20</b> has a substantially annular shape. In addition, each of the integrated bodies <b>100</b> also has a substantially annular shape.

0059As shown in <figref idref="DRAWINGS">FIG. 2</figref>, the integrated bodies <b>100</b>, each of which is comprised of one of the first coils <b>10</b> and the insulating films <b>11</b> covering the first coil <b>10</b>, and the second coils <b>20</b> are stacked together to form a stacked body <b>6</b>.

0060Further, as shown in <figref idref="DRAWINGS">FIGS. 1 and 4</figref>, the transformer <b>1</b> also includes a core <b>3</b> that is made of a magnetic material, such as ferrite, and arranged to cover the stacked body <b>6</b>.

0061Specifically, in the present embodiment, the core <b>3</b> is comprised of a pair of core pieces <b>30</b> that are respectively arranged on opposite sides of the stacked body <b>6</b> in the winding axial direction so as to together sandwich the stacked body <b>6</b> in the winding axial direction.

0062Each of the core pieces <b>30</b> includes a center magnetic leg <b>31</b> and a pair of side magnetic legs <b>32</b>. The center magnetic leg <b>31</b> is inserted into the radially inner space of the stacked body <b>6</b>, while the side magnetic legs <b>32</b> are located radially outside of the stacked body <b>6</b> so as to be respectively positioned on opposite sides of the stacked body <b>6</b>.

0063Each of the first coils <b>10</b> is formed by stacking two coil segments, each of which is obtained by punching a metal plate into a coil shape, in the thickness direction thereof and joining a corresponding pair of ends of the two coil segments.

0064Specifically, as shown in <figref idref="DRAWINGS">FIGS. 2</figref>, <b>7</b> and <b>8</b>, each of the first coils <b>10</b> is formed by stacking a large-linewidth electric conductor plate <b>12</b> and a small-linewidth electric conductor plate <b>13</b> in their thickness direction with an insulating film <b>11</b> interposed therebetween. The linewidth of the small-linewidth electric conductor plate <b>13</b> is less than or equal to half the linewidth of the large-linewidth electric conductor plate <b>12</b>. Moreover, the large-linewidth electric conductor plate <b>12</b> is substantially annular-shaped so that the number of turns of the plate <b>12</b> is equal to 1. On the other hand, the small-linewidth electric conductor plate <b>13</b> is substantially spiral-shaped so that the number of turns of the plate <b>13</b> is equal to 2. Further, one end of the large-linewidth electric conductor plate <b>12</b> is electrically connected, for example by welding, to one end of the small-linewidth electric conductor plate <b>13</b>. Consequently, the total number of turns of the first coil <b>13</b> is equal to 3.

0065Referring to <figref idref="DRAWINGS">FIGS. 2 and 3</figref>, each of the integrated bodies <b>100</b> is formed by stacking the large-linewidth and small-linewidth electric conductor plates <b>12</b> and <b>13</b> of the first coil <b>10</b> and three insulating films <b>11</b> so that each of the plates <b>12</b> and <b>13</b> is interposed between an adjacent pair of the insulating films <b>11</b> in the winding axial direction. Further, the three insulating films <b>11</b> are crimped on both the radially inside and radially outside of the integrated bodies <b>100</b>. In addition, the insulating films <b>11</b> are also crimped between the radially inner and radially outer turns of the small-linewidth electric conductor plate <b>13</b>. Moreover, an adhesive <b>112</b> is filled into all the void spaces of the integrated body <b>100</b> which are formed between the insulating films <b>11</b> and the large-linewidth and small-linewidth electric conductor plates <b>12</b> and <b>13</b>. Consequently, all of the insulating films <b>11</b> and the large-linewidth and small-linewidth electric conductor plates <b>12</b> and <b>13</b> are bonded together by the adhesive <b>112</b>.

0066In addition, as described previously, the corresponding ends of the large-linewidth and small-linewidth electric conductor plates <b>12</b> and <b>13</b> are joined together by, for example, welding, forming a joining portion therebetween. Though not shown in the figures, the joining portion extends to penetrate that of the insulating films <b>11</b> which is interposed between the large-linewidth and small-linewidth electric conductor plates <b>12</b> and <b>13</b>.

0067Referring to <figref idref="DRAWINGS">FIGS. 5-8</figref>, in the present embodiment, the pair of integrated bodies <b>100</b> are formed of a coil sheet <b>4</b>. More specifically, in the coil sheet <b>4</b>, the two integrated bodies <b>100</b> are connected with each other via a connecting portion <b>41</b>. As shown in <figref idref="DRAWINGS">FIGS. 9 and 10</figref>, the connecting portion <b>41</b> of the coil sheet <b>4</b> is folded in the thickness direction thereof, thereby superposing the integrated bodies <b>100</b> in the winding axial direction.

0068Moreover, as shown in <figref idref="DRAWINGS">FIG. 8</figref>, the connecting portion <b>41</b> of the coil sheet <b>4</b> includes therein a connecting electric conductor <b>411</b> that connects the first coils <b>10</b> included in the respective integrated bodies <b>100</b>. More specifically, in the present embodiment, the connecting electric conductor <b>411</b> is integrally formed with the small-linewidth electric conductor plates <b>13</b> of the first coils <b>10</b> into one piece. In other words, the connecting electric conductor <b>411</b> is punched out of the same metal plate as the small-linewidth electric conductor plates <b>13</b>.

0069In the present embodiment, all of the large-linewidth electric conductor plates <b>12</b>, the small-linewidth electric conductor plates <b>13</b> and the connecting electric conductor <b>411</b> have substantially the same thickness. Further, the thickness of those plates <b>12</b>, <b>13</b> and <b>411</b> is smaller than the thickness of those metal plates of which the second coils <b>20</b> are formed. More specifically, the thickness of the plates <b>12</b>, <b>13</b> and <b>411</b> is in the range of 0.3 to 0.5 mm, while the thickness of the metal plates forming the second coils <b>20</b> is in the range of 1 to 2 mm.

0070As shown in <figref idref="DRAWINGS">FIG. 5</figref>, in the coil sheet <b>4</b>, there are provided two coil terminals <b>14</b> that protrude respectively from the integrated bodies <b>100</b> in a direction perpendicular to both the winding axial direction and the extending direction (or the longitudinal direction) of the connecting portion <b>41</b>. Moreover, both the coil terminals <b>14</b> protrude toward the same side in the direction and are both exposed from the insulating films <b>11</b>. Further, as shown in <figref idref="DRAWINGS">FIG. 7</figref>, both the coil terminals <b>14</b> are integrally formed with the large-linewidth electric conductor plates <b>12</b> of the first coils <b>10</b> into one piece. In other words, both the coil terminals <b>14</b> are punched out of the same metal plate as the large-linewidth electric conductor plates <b>12</b>. In addition, the coil terminals <b>14</b> respectively make up a pair of input terminals of the transformer <b>1</b>.

0071The insulating films <b>11</b> together completely cover the first coils <b>10</b> except for the coil terminals <b>14</b>. More specifically, the insulating films <b>11</b> cover not only the major surfaces of the first coils <b>10</b> which are perpendicular to the winding axial direction (or to the thickness direction of the large-linewidth and small-linewidth electric conductor plates <b>12</b> and <b>13</b>), but also the radially inner and outer surfaces of the first coils <b>10</b>. Moreover, the connecting electric conductor <b>411</b> that connects the first coils <b>10</b> is also completely covered by an insulating film <b>11</b>. In addition, the insulating films <b>11</b> are made of an electrically insulative resin, such as a polyimide resin and an epoxy resin.

0072As described previously, for each of the first coils <b>10</b>, the total number of turns of the first coil <b>13</b> is equal to 3. Moreover, the two first coils <b>10</b> are electrically connected in series with each other via the connecting electric conductor <b>411</b>. Therefore, the total number of turns of the first coils <b>10</b> is equal to 6. In addition, as shown in <figref idref="DRAWINGS">FIGS. 9 and 10</figref>, after the two integrated bodies <b>100</b> are brought into superposition by folding the coil sheet <b>4</b> at the connecting portion <b>41</b>, the winding directions of the first coils <b>10</b> are the same.

0073Referring back to <figref idref="DRAWINGS">FIGS. 2 and 4</figref>, each of the second coils <b>20</b> is formed by punching a metal plate into a substantially annular shape. Consequently, for each of the second coils <b>20</b>, the number of turns of the second coil <b>20</b> is equal to 1. Moreover, the two second coils <b>20</b> are superposed with a gap formed therebetween in the winding axial direction (or in the thickness direction of the second coils <b>20</b>). Further, as will be described in detail later, the two second coils <b>20</b> are electrically connected to each other. Consequently, the total number of turns of the two second coils <b>20</b> is equal to 2.

0074In the present embodiment, the diameter of the second coils <b>20</b> is set to be smaller than that of the integrated bodies <b>100</b> so that the radially outer peripheries of the second coils <b>20</b> are positioned radially inside of the radially outer peripheries of the insulating films <b>11</b> and the radially inner peripheries of the second coils <b>20</b> are positioned radially outside of the radially inner peripheries of the insulating films <b>11</b>. That is, the second coils <b>20</b> protrude neither radially outward nor radially inward from the insulating films <b>11</b> of the integrated bodies <b>100</b>. In addition, when viewed along the winding axial direction, the radially outer peripheries of the second coils <b>20</b> substantially coincide with the radially outer peripheries of the first coils <b>10</b> and the radially inner peripheries of the second coils <b>20</b> substantially coincide with the radially inner peripheries of the first coils <b>10</b>.

0075Moreover, in the present embodiment, as shown in <figref idref="DRAWINGS">FIG. 11</figref>, the transformer <b>1</b> is mounted on a heat sink <b>7</b>. Further, as shown in <figref idref="DRAWINGS">FIG. 12</figref>, the second coils <b>20</b> of the transformer <b>1</b> are thermally connected to the heat sink <b>7</b>.

0076More specifically, each of the second coils <b>20</b> has a connecting terminal <b>23</b> and a coil terminal <b>24</b> that protrude from the substantially-annular main body of the second coil <b>20</b>. The connecting terminals <b>23</b> of the second coils <b>20</b> are superposed and aligned with each other, and fixed to a terminal block <b>71</b> of the heat sink <b>7</b> by means of a pair of screws <b>22</b>. Consequently, the second coils <b>20</b> are electrically connected to each other at the connecting terminals <b>23</b>; they are also fixed to and thereby thermally connected to the heat sink <b>7</b> at the connecting terminals <b>23</b>. In addition, the heat sink <b>7</b> may be implemented by a wall portion of a cooler that has formed therein a coolant passage for circulating a coolant.

0077Moreover, the second coils <b>20</b> are also mechanically connected to each other at the connecting terminals <b>23</b>, thereby becoming one integrated body. Further, the coil terminals <b>24</b> of the second coils <b>20</b> respectively make up a pair of output terminals of transformer <b>1</b>. In addition, both the connecting terminals <b>23</b> of the second coils <b>20</b> are grounded via the heat sink <b>7</b>.

0078As shown in <figref idref="DRAWINGS">FIG. 11</figref>, when viewed along the winding axial direction, all of the connecting terminals <b>23</b> and coil terminals <b>24</b> of the second coils <b>20</b> protrude from the respective substantially-annular main bodies of the second coils <b>20</b> on the same side of the core <b>3</b>.

0079Further, when viewed along the winding axial direction, the connecting terminals <b>23</b> and coil terminals <b>24</b> of the second coils <b>20</b> protrude on the opposite side of the core <b>3</b> to the coil terminals <b>14</b> of the first coils <b>10</b>.

0080Furthermore, as shown in <figref idref="DRAWINGS">FIGS. 1 and 2</figref>, the first coils <b>10</b> and the second coils <b>20</b> are stacked so that the large-linewidth electric conductor plates <b>12</b> respectively face the second coils <b>20</b>. In other words, the integrated bodies <b>100</b> are arranged so that the large-linewidth electric conductor plates <b>12</b> are respectively in contact with the second coils <b>20</b> via the insulating films <b>11</b> interposed therebetween.

0081Next, the advantages of the transformer <b>1</b> according to the present embodiment will be described.

0082In the present embodiment, the transformer <b>1</b> includes the pair of first coils <b>10</b> and the pair of second coils <b>20</b> that are stacked so that the pair of second coils <b>20</b> is interposed between the first coils <b>10</b> in the common winding axial direction of the first and second coils <b>10</b> and <b>20</b>. Each of the first coils <b>10</b> is covered by the insulating films <b>11</b> and integrated with the insulating films <b>11</b> into one integrated body <b>100</b>, so that the first coils <b>10</b> are electrically insulated from the second coils <b>20</b>.

0083With the above configuration, electrical insulation between the first coils <b>10</b> and the second coils <b>20</b> is secured by means of the thin insulating films <b>11</b> that cover the first coils <b>10</b>. Moreover, since the pair of second coils <b>20</b> is interposed between the first coils <b>10</b> in the winding axial direction, the second coils <b>20</b> are prevented from making contact with the core pieces <b>30</b> that are arranged with the stacked body <b>6</b> of the first and second coils <b>10</b> and <b>20</b> interposed therebetween in the winding axial direction. Consequently, electrical insulation between the second coils <b>20</b> and the core pieces <b>30</b> is secured without employing any additional insulating means. In addition, electrical insulation between the first coils <b>10</b> and the core pieces <b>30</b> is also secured by means of the thin insulating films <b>11</b> that cover the first coils <b>10</b>.

0084As a result, it becomes possible to secure the electrical insulation between the first coils <b>10</b>, the second coils <b>20</b> and the core pieces <b>30</b> without employing bobbins and thus without increasing the size of the transformer <b>1</b>. Moreover, since each of the first coils <b>10</b> is integrated with the insulating films <b>11</b> into one integrated body <b>100</b>, the parts count of the transformer <b>1</b> is prevented from increasing and the assembly process of the transformer <b>1</b> is prevented from becoming complicated.

0085Accordingly, with the above configuration, it is possible to minimize both the size and parts count of the transformer <b>1</b> and simplify the assembly process of the transformer <b>1</b> while securing the electrical insulation between the first coils <b>10</b>, the second coils <b>20</b> and the core pieces <b>30</b> without employing bobbins.

0086Further, in the present embodiment, each of the first coils <b>10</b> is comprised of the large-linewidth electric conductor plate <b>12</b> and the small-linewidth electric conductor plate <b>13</b> that are stacked in the winding axial direction with one insulating film <b>11</b> interposed therebetween. In addition, the large-linewidth and small-linewidth electric conductor plates <b>12</b> and <b>13</b> can be considered as the coil segments that together make up the first coil <b>10</b>.

0087With the above configuration, it is possible to increase the number of turns of each of the first coils <b>10</b> without unnecessarily increasing the thickness of each of the first coils <b>10</b> in the winding axial direction.

0088More specifically, if each of the first coils <b>10</b> was made up of a single electric conductor plate that is spiral-shaped as the small-linewidth electric conductor plate <b>13</b> shown in <figref idref="DRAWINGS">FIG. 8</figref>, it would be necessary to lead out the coil terminal <b>14</b> or the connecting electric conductor <b>411</b> from the radially inner end of the single electric conductor plate in the winding axial direction. Consequently, a certain thickness in the winding axial direction would be sacrificed only for the purpose of leading out the coil terminal <b>14</b> or the connecting electric conductor <b>411</b>. In comparison, in the present embodiment, each of the first coils <b>10</b> is comprised of the large-linewidth and small-linewidth electric conductor plates <b>12</b> and <b>13</b> that are stacked in the winding axial direction; that end of the large-linewidth electric conductor plate <b>12</b> which does not make up the coil terminal <b>14</b> is electrically connected to the radially inner end of the small-linewidth electric conductor plate <b>13</b>. Consequently, no thickness in the winding axial direction is sacrificed only for the purpose of leading out the coil terminal <b>14</b> or the connecting electric conductor <b>411</b>.

0089In the present embodiment, the integrated bodies <b>100</b> and the second coils <b>20</b> are each substantially annular-shaped. Moreover, the diameter of the second coils <b>20</b> is set to be less than that of the integrated bodies <b>100</b> so that the radially outer peripheries of the second coils <b>20</b> are positioned radially inside of the radially outer peripheries of the insulating films <b>11</b> and the radially inner peripheries of the second coils <b>20</b> are positioned radially outside of the radially inner peripheries of the insulating films <b>11</b>.

0090With the above configuration, the second coils <b>20</b> protrude neither radially outward nor radially inward from the insulating films <b>11</b> of the integrated bodies <b>100</b>. Consequently, the second coils <b>20</b> are prevented from making contact with the center magnetic legs <b>31</b> of the core pieces <b>30</b> located on the radially inside of the insulating films <b>11</b> and the side magnetic legs <b>32</b> of the core pieces <b>30</b> located on the radially outside of the insulating films <b>11</b>. As a result, the electrical insulation between the second coils <b>20</b> and the core pieces <b>30</b> can be reliably secured.

0091In the present embodiment, both the integrated bodies <b>100</b> are formed of the coil sheet <b>4</b>, in which the integrated bodies <b>100</b> are connected with each other via the connecting portion <b>41</b>. The coil sheet <b>4</b> is folded at the connecting portion <b>41</b> so that the integrated bodies <b>100</b> are superposed in the winding axial direction. Moreover, the connecting portion <b>41</b> of the coil sheet <b>4</b> includes therein the connecting electric conductor <b>411</b> that connects the first coils <b>10</b> included in the respective integrated bodies <b>100</b>.

0092With the above configuration, it is possible to easily form both the integrated bodies <b>100</b> at the same time by stacking the large-linewidth and small-linewidth electric conductor plates <b>12</b> and <b>13</b> and the insulating films <b>11</b>. Moreover, it is possible to easily handle both the integrated bodies <b>100</b> as a single part during the assembly process of the transformer <b>1</b>. In addition, it is possible to easily make the electrical connection between the first coils <b>100</b> included in the respective integrated bodies <b>100</b>.

0093In the present embodiment, in the coil sheet <b>4</b>, there are provided the two coil terminals <b>14</b> that protrude respectively from the integrated bodies <b>100</b> in the direction perpendicular to both the winding axial direction and the extending direction of the connecting portion <b>41</b>.

0094With the above configuration, it is possible to improve the degree of freedom in setting the shape and the protruding amount of the coil terminals <b>14</b>. In other words, it is possible to improve the design freedom of the coil terminals <b>14</b>.

0095In the present embodiment, each of the first coils <b>10</b> is comprised of the large-linewidth electric conductor segment <b>12</b> and the small-linewidth electric conductor segment <b>13</b> that are stacked in the winding axial direction. The second coils <b>20</b> are directly thermally connected to the heat sink <b>7</b>. The first and second coils <b>10</b> and <b>20</b> are stacked so that the large-linewidth electric conductor plates <b>12</b> of the first coils <b>10</b> respectively face the second coils <b>20</b>.

0096With the above configuration, the heat transfer area between the first coils <b>10</b> and the second coils <b>20</b> is increased in comparison with a case where the small-linewidth electric conductor plates <b>13</b> are arranged to respectively face the second coils <b>20</b>. Consequently, it is possible to more effectively dissipate heat generated by the first coils <b>10</b> via the second coils <b>20</b> and the heat sink <b>7</b>.

0097In the present embodiment, as shown in <figref idref="DRAWINGS">FIG. 11</figref>, when viewed along the winding axial direction, the connecting terminals <b>23</b> and coil terminals <b>24</b> of the second coils <b>20</b> protrude on the opposite side of the core <b>3</b> to the coil terminals <b>14</b> of the first coils <b>10</b>.

0098With the above configuration, it is possible to more reliably secure the electrical insulation between the first coils <b>10</b> and the second coils <b>20</b>.

0099Further, in the present embodiment, when viewed along the winding axial direction, all of the connecting terminals <b>23</b> and coil terminals <b>24</b> of the second coils <b>20</b> protrude on the same side of the core <b>3</b>.

0100With the above configuration, it is possible to easily form the main bodies of the second coils <b>20</b> into the substantially annular shape, thereby securing a high yield rate of the second coils <b>20</b>.

Second Embodiment

0101This embodiment illustrates a transformer <b>1</b> which has almost the same configuration as the transformer <b>1</b> according to the first embodiment; accordingly, only the differences therebetween will be described hereinafter.

0102In the present embodiment, as shown in <figref idref="DRAWINGS">FIG. 13</figref>, each of the second coils <b>20</b> is bonded by an adhesive <b>5</b> to that one of the integrated bodies <b>100</b> which is adjacent to the second coil <b>20</b>.

0103More specifically, in the present embodiment, as shown in <figref idref="DRAWINGS">FIG. 14</figref>, on one major surface of the coil sheet <b>4</b>, the second coils <b>20</b> are respectively bonded by the adhesive <b>5</b> to the corresponding integrated bodies <b>100</b>. Then, the coil sheet <b>4</b> is folded at the connecting portion <b>41</b> so that the second coils <b>20</b> are superposed and face each other in the winding axial direction. Consequently, as shown in <figref idref="DRAWINGS">FIG. 13</figref>, in the resultant stacked body <b>6</b>, the pair of second coils <b>20</b> is interposed between the integrated bodies <b>100</b> in the winding axial direction. Thereafter, the stacked body <b>6</b> and the core <b>3</b> are assembled together so that the stacked body <b>6</b> is interposed between and thereby covered by the core pieces <b>30</b> of the core <b>3</b> in the winding axial direction (see <figref idref="DRAWINGS">FIGS. 1 and 4</figref>). As a result, the transformer <b>1</b> according to the present embodiment is obtained.

0104The above-described transformer <b>1</b> according to the present embodiment has the same advantages as the transformer <b>1</b> according to the first embodiment.

0105In addition, in the present embodiment, since the second coils <b>20</b> are respectively bonded by the adhesive <b>5</b> to the corresponding integrated bodies <b>100</b>, it is possible to easily handle all of the integrated bodies <b>100</b> and the second coils <b>20</b> as a single part during the process of assembling the stacked body <b>6</b> and the core <b>3</b>. Further, it is also possible to more effectively dissipate heat generated by the first coils <b>10</b> via the second coils <b>20</b> and the heat sink <b>7</b>.

Third Embodiment

0106This embodiment illustrates a transformer <b>1</b> which has almost the same configuration as the transformer <b>1</b> according to the first embodiment; accordingly, only the differences therebetween will be described hereinafter.

0107In the present embodiment, as shown in <figref idref="DRAWINGS">FIG. 15</figref>, the insulating films <b>11</b>, which cover the first coils <b>10</b>, have extensions <b>111</b> that extend in the winding axial direction along the outer surfaces of the center magnetic legs <b>31</b> of the core pieces <b>30</b> of the core <b>3</b>, so as to be radially interposed between the outer surfaces of the center magnetic legs <b>31</b> and the radially inner surfaces of the second coils <b>20</b>.

0108More specifically, in the present embodiment, as shown in <figref idref="DRAWINGS">FIG. 17</figref>, during the formation of the integrated bodies <b>100</b>, the insulating films <b>11</b> are applied so as to have center portions that extend radially inward from the radially inner surfaces of the first coils <b>10</b> to close the openings formed on the radially inside of the first coils <b>10</b>. Then, the center portions are radially cut into a plurality of pieces. Thereafter, the coil sheet <b>4</b> is folded at the connecting portion <b>41</b> to superpose the integrated bodies <b>100</b> in the winding axial direction; further, the second coils <b>20</b> are stacked with the integrated bodies <b>100</b> in the winding axial direction to form the stacked body <b>6</b> as shown in <figref idref="DRAWINGS">FIG. 16</figref>. Next, the stacked body <b>6</b> and the core <b>3</b> are assembled together to form the transformer <b>1</b> as shown in <figref idref="DRAWINGS">FIG. 15</figref>. During the assembly of the stacked body <b>6</b> and the core <b>3</b>, the center magnetic legs <b>31</b> of the core pieces <b>30</b> of the core <b>3</b> are inserted into the radially inner space of the stacked body <b>6</b>, pressing the pieces of the center portions of the insulating films <b>11</b>. Consequently, by the pressing force of the center magnetic legs <b>31</b>, the pieces of the center portions of the insulating films are deformed to extend in the winding axial direction along the outer surfaces of the center magnetic legs <b>31</b>, thereby making up the extensions <b>111</b>.

0109The above-described transformer <b>1</b> according to the present embodiment has the same advantages as the transformer <b>1</b> according to the first embodiment.

0110In addition, in the present embodiment, with the extensions <b>111</b> of the insulating films <b>11</b> radially interposed between the outer surfaces of the center magnetic legs <b>31</b> of the core pieces <b>30</b> and the radially inner surfaces of the second coils <b>20</b>, it is possible to more reliably secure the electrical insulation between the second coils <b>20</b> and the core pieces <b>30</b> of the core <b>3</b>.

Fourth Embodiment

0111This embodiment illustrates a transformer <b>1</b> which has almost the same configuration as the transformer <b>1</b> according to the first embodiment; accordingly, only the differences therebetween will be described hereinafter.

0112In the present embodiment, as shown in <figref idref="DRAWINGS">FIG. 18</figref>, the coil sheet <b>4</b> includes three integrated bodies <b>100</b> that are connected to one another via a pair of connecting portions <b>41</b> and aligned with each other in a direction parallel to the extending direction of the connecting portions <b>41</b>. Moreover, the pair of coil terminals <b>14</b> are arranged so as to protrude, in a direction perpendicular to both the winding axial direction and the extending direction of the connecting portions <b>41</b>, respectively from those two of the integrated bodies <b>100</b> which are respectively located at opposite ends of the coil sheet <b>4</b>. In addition, both the coil terminals <b>14</b> protrude toward the same side in the direction perpendicular to both the winding axial direction and the extending direction of the connecting portions <b>41</b>.

0113Furthermore, as shown in <figref idref="DRAWINGS">FIG. 19</figref>, the coil sheet <b>4</b> is folded twice at the connecting portions <b>41</b> so that the integrated bodies <b>100</b> are superposed in the winding axial direction. Then, each of the second coils <b>20</b> is inserted between an adjacent pair of the integrated bodies <b>100</b>. Consequently, the integrated bodies <b>100</b> are alternately arranged with the second coils <b>20</b> in the winding axial direction, forming the stacked body <b>6</b>. Thereafter, though not shown in the figures, the stacked body <b>6</b> and the core <b>3</b> are assembled together to form the transformer <b>1</b> according to the present embodiment.

0114The above-described transformer <b>1</b> according to the present embodiment has the same advantages as the transformer <b>1</b> according to the first embodiment.

0115In addition, the number of the integrated bodies <b>100</b> may be suitably set according to the design specification of the transformer <b>1</b>. For example, in one modification of the present embodiment, as shown in <figref idref="DRAWINGS">FIGS. 20 and 21</figref>, the coil sheet <b>4</b> includes four integrated bodies <b>100</b> that are connected to one another via three connecting portions <b>41</b>. In another modification, as shown in <figref idref="DRAWINGS">FIGS. 22 and 23</figref>, the coil sheet <b>4</b> includes five integrated bodies <b>100</b> that are connected to one another via four connecting portions <b>41</b>.

Fifth Embodiment

0116This embodiment illustrates a transformer <b>1</b> which has almost the same configuration as the transformer <b>1</b> according to the first embodiment; accordingly, only the differences therebetween will be described hereinafter.

0117In the first embodiment, the transformer <b>1</b> includes only the single stacked body <b>6</b>, in which the pair of second coils <b>20</b> is interposed between the integrated bodies <b>100</b> in the winding axial direction (see <figref idref="DRAWINGS">FIG. 2</figref>).

0118In comparison, in the present embodiment, as shown <figref idref="DRAWINGS">FIG. 24</figref>, the transformer <b>1</b> includes a pair of stacked bodies <b>6</b> that are stacked in the winding axial direction. Further, in each of the stacked bodies <b>6</b>, there is only a single second coil <b>20</b> interposed between two integrated bodies <b>100</b>. Furthermore, the stacked bodies <b>6</b> are electrically connected with each other. More specifically, the first coils <b>10</b> included in the integrated bodies <b>100</b> of one of the stacked bodies <b>6</b> are electrically connected with the first coils <b>10</b> included in the integrated bodies <b>100</b> of the other stacked body <b>6</b>; the second coils <b>20</b> of one of the stacked bodies <b>6</b> are electrically connected with the second coils <b>20</b> of the other stacked body <b>6</b>.

0119The above-described transformer <b>1</b> according to the present embodiment has the same advantages as the transformer <b>1</b> according to the first embodiment.

0120In addition, in the present embodiment, each of the stacked bodies <b>6</b> can function as a transformer element. That is, two transformer elements are covered by a single core <b>3</b>. Consequently, compared to the case of employing two transformers <b>1</b> each including a single transformer unit, both the size and part counts are reduced.

Sixth Embodiment

0121This embodiment illustrates a transformer <b>1</b> which has almost the same configuration as the transformer <b>1</b> according to the first embodiment; accordingly, only the differences therebetween will be described hereinafter. In the first embodiment, the transformer <b>1</b> has the pair of second coils <b>20</b> interposed between the integrated bodies <b>100</b> (or between the first coils <b>10</b>) in the winding axial direction (see <figref idref="DRAWINGS">FIG. 1</figref>).

0122In comparison, in the present embodiment, as shown <figref idref="DRAWINGS">FIG. 25</figref>, the transformer <b>1</b> has only a single second coil <b>20</b> interposed between the integrated bodies <b>100</b> in the winding axial direction.

0123The above-described transformer <b>1</b> according to the present embodiment has the same advantages as the transformer <b>1</b> according to the first embodiment.

0124In addition, the number of the second coils <b>20</b> interposed between the first coils <b>10</b> may be suitably set according to the design specification of the transformer <b>1</b>.

Seventh Embodiment

0125This embodiment illustrates a transformer <b>1</b> which has almost the same configuration as the transformer <b>1</b> according to the fourth embodiment; accordingly, only the differences therebetween will be described hereinafter.

0126In the fourth embodiment, the coil sheet <b>4</b> includes three or more integrated bodies <b>100</b>, but has only the pair of coil terminals <b>14</b> that protrude respectively from those two of the integrated bodies <b>100</b> which are respectively located at opposite ends of the coil sheet <b>4</b> (see <figref idref="DRAWINGS">FIGS. 18-23</figref>).

0127In comparison, in the present embodiment, as shown <figref idref="DRAWINGS">FIG. 26</figref>, the coil sheet <b>4</b> includes four integrated bodies <b>100</b> that are connected to one another via three connecting portions <b>41</b> and aligned with each other a direction parallel to the extending direction of the connecting portions <b>41</b>. Moreover, the coil sheet <b>4</b> has four coil terminals <b>14</b> that protrude respectively from the integrated bodies <b>100</b> in a direction perpendicular to both the winding axial direction and the extending direction of the connecting portions <b>41</b>. In other words, for each of the integrated bodies <b>100</b>, there is provided one coil terminal <b>14</b> that protrudes from the integrated body <b>100</b>. In addition, all the coil terminals <b>14</b> protrude toward the same side in the direction perpendicular to both the winding axial direction and the extending direction of the connecting portions <b>41</b>.

0128The above-described transformer <b>1</b> according to the present embodiment has the same advantages as the transformer <b>1</b> according to the fourth embodiment.

0129In addition, in the present embodiment, by providing more than two coil terminals <b>14</b> in the coil sheet <b>4</b>, it is possible to easily form one or more center taps of the transformer <b>1</b>.

0130It should be noted that the number of the coil terminals <b>14</b> may be suitably set according to the design specification of the transformer <b>1</b>.

Eighth Embodiment

0131This embodiment illustrates a transformer <b>1</b> which has almost the same configuration as the transformer <b>1</b> according to the first embodiment; accordingly, only the differences therebetween will be described hereinafter.

0132In the first embodiment, each of the integrated bodies <b>100</b> is formed in the shape of a substantially circular ring (see <figref idref="DRAWINGS">FIG. 5</figref>).

0133In comparison, in the present embodiment, as shown <figref idref="DRAWINGS">FIG. 27</figref>, each of the integrated bodies <b>100</b> is formed in the shape of a substantially rectangular ring. In addition, though not shown in the figures, each of the first coils <b>10</b> and the second coils <b>20</b> is also formed in the shape of a substantially rectangular ring.

0134The above-described transformer <b>1</b> according to the present embodiment has the same advantages as the transformer <b>1</b> according to the first embodiment.

0135In addition, the integrated bodies <b>100</b> may also have other shapes, for example, the shape of a substantially elliptical or hexagonal ring.

Ninth Embodiment

0136This embodiment illustrates a transformer <b>1</b> which has almost the same configuration as the transformer <b>1</b> according to the first embodiment; accordingly, only the differences therebetween will be described hereinafter.

0137In the first embodiment, the two coil terminals <b>14</b> protrude respectively from the integrated bodies <b>100</b> in a direction perpendicular to both the winding axial direction and the extending direction of the connecting portion <b>41</b>. Moreover, both the coil terminals <b>14</b> protrude toward the same side in the direction (see <figref idref="DRAWINGS">FIG. 5</figref>).

0138In comparison, in the present embodiment, as shown <figref idref="DRAWINGS">FIG. 28</figref>, the two coil terminals <b>14</b> protrude respectively from the integrated bodies <b>100</b> in a direction parallel to the extending direction of the connecting portion <b>41</b>. Moreover, the two coil terminals <b>14</b> protrude toward each other. In addition, it should be noted that the two coil terminals <b>14</b> may also be arranged to protrude toward the same side or toward opposite sides in the direction parallel to the extending direction of the connecting portion <b>41</b>.

0139The above-described transformer <b>1</b> according to the present embodiment has the same advantages as the transformer <b>1</b> according to the first embodiment.

0140In addition, in the present embodiment, the two coil terminals <b>14</b> are arranged in the vicinity of the integrated bodies <b>100</b>. Consequently, it is possible to secure a high yield rate in punching a single metal plate to form the coil terminals <b>14</b> and the large-linewidth electric conductor plates <b>12</b> of the integrated bodies <b>100</b>.

0141Furthermore, as shown in <figref idref="DRAWINGS">FIG. 29</figref>, it is also possible to arrange only one of the coil terminals <b>14</b> to protrude parallel to the extending direction of the connecting portion <b>41</b> while arranging the other coil terminal <b>14</b> to protrude in a direction perpendicular to both the winding axial direction and the extending direction of the connecting portion <b>41</b> as in the first embodiment.

0142While the above particular embodiments and modifications have been shown and described, it will be understood by those skilled in the art that various further modifications, changes, and improvements may be made without departing from the spirit of the invention.

0143For example, in the previous embodiments, the first coils <b>10</b> are configured as high voltage-side coils, and the second coils <b>20</b> are configured as low voltage-side coils.

0144However, it is also possible to configure the first coils <b>10</b> as low voltage-side coils and the second coils <b>20</b> as high voltage-side coils.