Patent Publication Number: US-8541977-B2

Title: Coil unit and electronic instrument

Description:
Japanese Patent Application No. 2007-189812 filed on Jul. 20, 2007, is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a coil unit utilized for non-contact power transmission using a coil, an electronic instrument, and the like. 
     Non-contact power transmission that utilizes electromagnetic induction to enable power transmission without metal-to-metal contact has been known. As application examples of non-contact power transmission, charging a portable telephone, charging a household appliance (e.g., telephone handset), and the like have been proposed. 
     Non-contact power transmission has a problem in that a transmission coil generates heat. Technologies for suppressing such heat generation have been proposed. JP-A-8-103028 discloses a design method that suppresses heat generation during non-contact charging. JP-A-8-148360 discloses technology that suppresses heat generation by adapting a suitable configuration of a coil and a magnetic material. JP-A-11-98705 discloses a non-contact charging device provided with an air-cooling mechanism. JP-A-2003-272938 discloses a structure in which a ceramic is disposed between a primary coil and a secondary coil to dissipate heat. JP-A-2005-110357 discloses the structure of a housing with an improved heat dissipation capability. 
     SUMMARY 
     According to one aspect of the invention, there is provided a coil unit comprising: 
     a planar coil that has a transmission side and a non-transmission side; 
     a magnetic sheet provided over the non-transmission side of the planar coil; and 
     a heat sink/magnetic shield plate stacked on a side of the magnetic sheet opposite to a side that faces the planar coil, the heat sink/magnetic shield plate dissipating heat generated by the planar coil and shielding magnetism by absorbing a magnetic flux that has not been absorbed by the magnetic sheet, 
     the heat sink/magnetic shield plate having a thickness larger than that of the magnetic sheet. 
     According to another aspect of the invention, there is provided a coil unit comprising: 
     a coil; 
     a magnetic material disposed near the coil; and 
     a member disposed so that the magnetic material is placed between the coil and the member, 
     the member having a thickness larger than that of the magnetic material. 
     According to another aspect of the invention, there is provided an electronic instrument comprising one of the above coil units. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a view schematically showing a charger and a charging target. 
         FIG. 2  is an exploded oblique view showing a coil unit. 
         FIG. 3A  is an oblique view showing a coil unit from the front side, and 
         FIG. 3B  is an oblique view showing a coil unit from the back side. 
         FIG. 4  is an oblique view showing a substrate from the front side. 
         FIG. 5  is an oblique view showing a substrate from the back side. 
         FIG. 6  is a view showing a modification in which a temperature detection element is provided on the front side of a substrate. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT 
     Several aspects of the invention may provide a coil unit that exhibits excellent heat dissipation capability and can be reduced in thickness, and an electronic instrument using the coil unit. 
     According to one embodiment of the invention, there is provided a coil unit comprising: 
     a planar coil that has a transmission side and a non-transmission side; 
     a magnetic sheet provided over the non-transmission side of the planar coil; and 
     a heat sink/magnetic shield plate stacked on a side of the magnetic sheet opposite to a side that faces the planar coil, the heat sink/magnetic shield plate dissipating heat generated by the planar coil and shielding magnetism by absorbing a magnetic flux that has not been absorbed by the magnetic sheet, 
     the heat sink/magnetic shield plate having a thickness larger than that of the magnetic sheet. 
     Heat generated by the planar coil is dissipated through solid heat conduction of the magnetic sheet and the heat sink/magnetic shield plate stacked on the planar coil. The heat sink/magnetic shield plate has a function of a heat sink and a function of a magnetic shield that absorbs a magnetic flux which has not been absorbed by the magnetic sheet. As the material for the heat sink/magnetic shield plate, a non-magnetic material (i.e., a generic name for a diamagnetic material, a paramagnetic material, and an antiferromagnetic material) may be used. Aluminum or copper may be suitably used as the material for the heat sink/magnetic shield plate. 
     The heat sink/magnetic shield plate is formed to have a thickness larger than that of the magnetic sheet. A magnetic flux which has not been absorbed by the magnetic sheet is absorbed by the heat sink/magnetic shield plate. In this case, the heat sink/magnetic shield plate is inductively heated by a magnetic flux which has not been absorbed by the magnetic sheet. However, since the heat sink/magnetic shield plate has a given thickness, the heat sink/magnetic shield plate has a relatively large heat capacity and a low heat generation temperature. Moreover, the heat sink/magnetic shield plate easily dissipates heat due to its dissipation characteristics. Therefore, heat generated by the planar coil can be dissipated efficiently. Moreover, the coil unit can be formed to have a thickness as thin as about 1.65 mm, for example. 
     The coil unit may further include: 
     a substrate, the heat sink/magnetic shield plate being secured on the substrate; and 
     a temperature detection element provided on the substrate, the temperature detection element detecting the temperature of the planar coil due to heat generation that is transferred through solid heat conduction of the magnetic sheet and the heat sink/magnetic shield plate. 
     This enables detection of an abnormality when the temperature of the heat sink/magnetic shield plate increases to a large extent due to an increase in temperature of the coil caused by insertion of a foreign object, for example. 
     In the coil unit, 
     heat transfer conductive patterns may be formed on a front side and a back side of the substrate, the front side facing the heat sink/magnetic shield plate; and 
     the temperature detection element may be provided on the back side of the substrate. 
     According to this configuration, heat generated by the planar coil is transferred to the temperature detection element through solid heat conduction of the magnetic sheet, the heat sink/magnetic shield plate, the heat transfer conductive pattern on the front side, the substrate, and the heat transfer conductive pattern on the back side. Moreover, since the temperature detection element is provided on the back side of the substrate, the temperature detection element does not interfere with the heat sink/magnetic shield plate. 
     In the coil unit, the heat transfer conductive patterns formed on the front side and the back side of the substrate may be connected via a through-hole formed through the substrate. The substrate is an insulator and has low heat transfer properties. However, the heat transfer properties can be improved by providing the through-hole. 
     In the coil unit, a depression may be formed in a side of the heat sink/magnetic shield plate that faces the substrate; and the temperature detection element may be provided on a front side of the substrate and disposed inside the depression formed in the heat sink/magnetic shield plate, the front side of the substrate facing the heat sink/magnetic shield plate. According to this configuration, even if the temperature detection element is provided on the front side of the substrate, the temperature detection element does not interfere with the heat sink/magnetic shield plate. When the planar coil has an air-core section at the center of the planar coil, a hole may be formed in the heat sink/magnetic shield plate as a depression at a position corresponding to the air-core section. According to one embodiment of the invention, since the heat sink/magnetic shield plate has a given thickness, the heat sink/magnetic shield plate can have a thickness sufficient to receive the temperature detection element. When employing the above structure, a heat transfer conductive pattern may be formed on the front side of the substrate. 
     In the coil unit, 
     the temperature detection element may be an element that breaks or suppresses power supplied to the planar coil based on the temperature of the planar coil due to heat generation. This makes it possible to stop or suppress power supplied to the planar coil when an abnormality has occurred. Examples of the temperature detection element include a thermistor of which the resistance increases at a high temperature to suppress or break current, and an element (e.g., fuse) that is melted at a high temperature to break current. 
     The coil unit may further include a covering member that covers an edge of the magnetic sheet. The edge of the magnetic sheet is fragile and is easily removed. However, the material of the edge of the magnetic sheet can be prevented from being scattered by covering the edge of the magnetic sheet with the protective sheet. The covering member may be formed using an insulating sheet or a sealing member (e.g., silicone). 
     In the coil unit, the covering member may be a protective sheet having a hole that receives the planar coil, the protective sheet covering edges of the magnetic sheet and the heat sink/magnetic shield plate and securing the magnetic sheet and the heat sink/magnetic shield plate on a front side of the substrate. According to this configuration, the covering member can also be used as a member for securing the magnetic sheet and the heat sink/magnetic shield plate. 
     In one embodiment of the invention, a plurality of the magnetic sheets may be provided. When magnetic saturation occurs using only one magnetic sheet when a large current flows through the planar coil (e.g., when power is turned ON), a leakage flux can be reduced by providing a plurality of magnetic sheets. The heat sink/magnetic shield plate has a thickness larger than the total thickness of the plurality of magnetic sheets. 
     In the coil unit, 
     the planar coil may have an inner end lead line and an outer end lead line, the inner end lead line being provided over the non-transmission side of the planar coil; and 
     a spacer member may be disposed between the planar coil and the magnetic sheet, the spacer member having a thickness substantially equal to the thickness of the inner end lead line. 
     This allows the transmission side of the planar coil to be made flat so that the primary coil and the secondary coil are easily disposed adjacently when performing non-contact power transmission. Although the non-transmission side of the planar coil protrudes due to the inner end lead line, the non-transmission side of the planar coil can be made flat and caused to adhere to the magnetic sheet by utilizing the spacer member. The heat transfer properties can thus be maintained. 
     In the coil unit, 
     the substrate may have a mounting surface provided with a mounted component in an area that extends from an area that faces the heat sink/magnetic shield plate, and the mounting surface may be provided on the back side of the substrate. 
     According to this configuration, since only the planar coil, the magnetic sheet, and the heat sink/magnetic shield plate protrude from the front side of the substrate, the primary coil and the secondary coil are easily disposed adjacently when performing non-contact power transmission. 
     According to another embodiment of the invention, there is provided a coil unit comprising: 
     a coil; 
     a magnetic material disposed near the coil; and 
     a member disposed so that the magnetic material is placed between the coil and the member, 
     the member having a thickness larger than that of the magnetic material. 
     According to another embodiment of the invention, the magnetic sheet according to one embodiment of the invention may be the magnetic material, and the heat sink/magnetic shield plate may be the member disposed so that the magnetic material is placed between the coil and the member. In this case the member is inductively heated by a magnetic flux which has not been absorbed by the magnetic material. However, since the member thicker than the magnetic material has a given thickness, the member has a relatively large heat capacity and a low heat generation temperature. Therefore, the member can dissipate heat generated by the planar coil without overheating. 
     According to another embodiment of the invention, there is provided an electronic instrument comprising one of the above coil units. 
     Preferred embodiments of the invention are described in detail below. Note that the following embodiments do not in any way limit the scope of the invention defined by the claims laid out herein. Note that all elements of the following embodiments should not necessarily be taken as essential requirements for the invention. 
     1. Charging System 
       FIG. 1  is a view schematically showing a charger  10  and a charging target  20 . A secondary-side electronic instrument (e.g., portable telephone  20 ) is charged using a primary-side electronic instrument (e.g., charger  10 ) by non-contact power transmission utilizing electromagnetic induction that occurs between a coil of a coil unit  12  of the charger  10  and a coil of a coil unit  22  of the portable telephone  20 . 
     Opposite sides of the coil units  12  and  22  when performing non-contact power transmission as shown in  FIG. 1  are referred to as transmission sides. In  FIG. 1 , the upper side of the coil unit  12  is the transmission side, and the lower side of the coil unit  22  is the transmission side. The side opposite to the transmission side is referred to as a non-transmission side. 
     2. Structure of Coil Unit 
     The configurations of the coil units  12  and  22  are described below with reference to  FIGS. 2 ,  3 A, and  3 B taking the coil unit  12  as an example. Note that the structure shown in  FIG. 2  may also be applied to the coil unit  22 . 
       FIG. 2  is an exploded oblique view showing the coil unit  12 ,  FIG. 3A  is an oblique view showing the coil unit  12  from the front side, and  FIG. 3B  is an oblique view showing the coil unit  12  from the back side. 
     In  FIG. 2 , the coil unit  12  is basically configured to include a planar coil (coil)  30  that has a transmission side  31  and a non-transmission side  32 , a magnetic sheet  40  provided over the non-transmission side  32  of the planar coil  30 , and a heat sink/magnetic shield plate  50  stacked on the side of the magnetic sheet opposite to the side that faces the planar coil  30 . 
     The planar coil  30  is not particularly limited insofar as the planar coil  30  is a flat (planar) coil. For example, an air-core coil formed by winding a single-core or multi-core coated coil wire in a plane may be used as the planar coil  30 . In this embodiment, the planar coil  30  has an air-core section  33  at the center of the planar coil  30 . The planar coil  30  includes an inner end lead line  34  connected to the inner end of the spiral, and an outer end lead line  35  connected to the outer end of the spiral. In this embodiment, the inner end lead line  34  is provided toward the outside in the radial direction through the non-transmission side  32  of the planar coil  30 . This allows the transmission side  31  of the planar coil  30  to be made flat so that the primary coil and the secondary coil are easily disposed adjacently when performing non-contact power transmission. 
     The magnetic sheet (magnetic material)  40  disposed over the non-transmission side  32  of the planar coil  30  is formed to have a size sufficient to cover the planar coil  30 . The magnetic sheet  40  receives a magnetic flux from the planar coil  30  to increase the inductance of the planar coil  30 . A soft magnetic material is preferably used as the material for the magnetic sheet  40 . A soft magnetic ferrite material or a soft magnetic metal material may be used as the material for the magnetic sheet  40 . 
     The heat sink/magnetic shield plate  50  is disposed on the side of the magnetic sheet  40  opposite to the side that faces the planar coil  30 . The thickness of the heat sink/magnetic shield plate  50  is larger than that of the magnetic sheet  40 . The heat sink/magnetic shield plate  50  has a function of a heat sink and a function of a magnetic shield that absorbs a magnetic flux which has not been absorbed by the magnetic sheet  40 . As the material for the heat sink/magnetic shield plate  50 , a non-magnetic material (i.e., a generic name for a diamagnetic material, a paramagnetic material, and an antiferromagnetic material) may be used. Aluminum or copper may be suitably used as the material for the heat sink/magnetic shield plate  50 . 
     Heat generated by the planar coil  30  when a current is caused to flow through the planar coil  30  is dissipated utilizing solid heat conduction of the magnetic sheet  40  and the heat sink/magnetic shield plate  50  stacked on the planar coil  30 . A magnetic flux which has not been absorbed by the magnetic sheet  40  is absorbed by the heat sink/magnetic shield plate  50 . In this case, the heat sink/magnetic shield plate  50  is inductively heated by a magnetic flux which has not been absorbed by the magnetic sheet  40 . However, since the heat sink/magnetic shield plate  50  has a given thickness, the heat sink/magnetic shield plate  50  has a relatively large heat capacity and a low heat generation temperature. Moreover, the heat sink/magnetic shield plate  50  easily dissipates heat due to its dissipation characteristics. Therefore, heat generated by the planar coil  30  can be dissipated efficiently. In this embodiment, the total thickness of the planar coil  30 , the magnetic sheet  40 , and the heat sink/magnetic shield plate  50  can be reduced to about 1.65 mm, for example. 
     In this embodiment, a spacer member  60  having a thickness substantially equal to the thickness of the inner end lead line  34  is provided between the planar coil  30  and the magnetic sheet  40 . The spacer member  60  is formed in the shape of a circle having almost the same diameter as that of the planar coil  30 , and has a slit  62  so as to avoid at least the inner end lead line  34 . The spacer member  60  is a double-sided adhesive sheet, for example. The spacer member  60  bonds the planar coil  30  to the magnetic sheet  40 . 
     In this embodiment, although the non-transmission side  32  of the planar coil  30  protrudes due to the inner end lead line  34 , the non-transmission side  32  of the planar coil  30  can be made flat and caused to adhere to the magnetic sheet  40  by utilizing the spacer member  60 . The heat transfer properties can thus be maintained. 
     In this embodiment, the coil unit  12  includes a substrate  100  on which the heat sink/magnetic shield plate  50  is secured. In this case, the heat sink/magnetic shield plate  50  dissipates heat to the substrate  100 . The substrate  100  has coil connection pads  103  connected to the inner end lead line  34  and the outer end lead line  35  of the planar coil  30 . 
     The coil unit  12  includes a protective sheet  70  that covers the edge of the magnetic sheet  40  and the heat sink/magnetic shield plate  50  and secures (bonds) the magnetic sheet  40  and the heat sink/magnetic shield plate  50  to a surface  101  of the substrate  100 . In this case, the inner end lead line  34  and the outer end lead line  35  of the planar coil  30  are connected to the coil connection pads  103  of the substrate  100  to pass over the protective sheet  70  (see  FIG. 3A ). The protective sheet  70  has a hole  71  that receives the planar coil  30 . The protective sheet  70  also functions as a covering member that covers the edge of the magnetic sheet  40 . The edge of the magnetic sheet  40  is fragile and is easily removed. However, the material of the edge of the magnetic sheet  40  can be prevented from being scattered by covering the edge of the magnetic sheet  40  with the protective sheet  70  (i.e., covering member). The covering member may be formed of a sealing member (e.g., silicone) instead of the protective sheet  70 . 
     The coil unit  12  is produced as follows. The magnetic sheet  40  and the heat sink/magnetic shield plate  50  are stacked on the substrate  100 . In this case, the substrate  100  is positioned on a jig (not shown) by utilizing holes  104  formed at the four corners of the substrate  100 . Positioning pins that protrude from the jig are fitted into the holes  104  (e.g., four holes) formed in the substrate  100 , holes  51  (e.g., four holes) formed in the heat sink/magnetic shield plate  50 , and holes  107  formed in the substrate  100  corresponding to the holes  51 . The heat sink/magnetic shield plate  50  is thus positioned with respect to the substrate  100  placed on the jig. The magnetic sheet  40  is then placed on the heat sink/magnetic shield plate  50 , and the magnetic sheet  40  is covered with the protective sheet  70  so that the magnetic sheet  40  and the heat sink/magnetic shield plate  50  are secured on the substrate  100  using the protective sheet  70 . 
     The planar coil  30  is then secured (bonded) on the magnetic sheet  40  through the spacer member  60  inside the hole  71  formed in the protective sheet  70 . The inner end lead line  34  and the outer end lead line  35  of the planar coil  30  are then connected to the coil connection terminals  103  of the substrate  100  to obtain the coil unit  12 . 
     As shown in  FIG. 3B , the coil unit  12  according to this embodiment includes a temperature detection element  80  that is provided on a back side  102  of the substrate  100  and detects the temperature of the planar coil  30  due to heat generation that is transferred through solid heat conduction of the magnetic sheet  40  and the heat sink/magnetic shield plate  50 , for example. Even if a foreign object or the like has been inserted between the primary coil and the secondary coil so that the temperature of the primary-side planar coil  30  has increased abnormally, the abnormality can be detected by the temperature detection element  80 . Power transmission may be stopped when the temperature detection element  80  has detected that the temperature of the planar coil  30  has increased abnormally. The temperature detection element  80  is not particularly limited insofar as the temperature detection element  80  has a temperature detecting function. In this embodiment, the temperature detection element  80  is formed using a thermistor of which the resistance increases at a high temperature to suppress or break current, for example. An element (e.g., fuse) that is melted at a high temperature to break current may be used instead of a thermistor. This makes it possible to break or suppress a current that flows through the planar coil  30  when the temperature of the heat sink/magnetic shield plate has abnormally increased due to an increase in temperature of the planar coil  30  caused by insertion of a foreign object or the like. 
       FIG. 4  is a wiring pattern diagram showing the front side  101  of the substrate  100 , and  FIG. 5  is a wiring pattern diagram showing the back side  102  of the substrate  100 . As shown in  FIGS. 4 and 5 , heat transfer conductive patterns  110  and  111  are formed on the front side  101  and the back side  102  of the substrate  100  over almost the entire area that faces the heat sink/magnetic shield plate  50 . The heat transfer conductive patterns  110  and  111  on the front side  101  and the back side  102  of the substrate  100  are connected via a plurality of through-holes  112 . 
     Thermistor wiring patterns  113 A and  113 B insulated from the heat sink/magnetic shield plate  50  and the heat transfer conductive pattern  110  are formed on the front side  101  of the substrate  100  shown in  FIG. 4 . The thermistor wiring patterns  113  are connected to thermistor connection patterns  116 A and  116 B formed on the back side  102  of the substrate  100  shown in  FIG. 5  via two through-holes  114  and  115 . The thermistor connection patterns  116 A and  116 B are insulated from the heat transfer conductive pattern  111 . 
     According to this configuration, heat generated by the planar coil  30  is transferred to the temperature detection element  80  (omitted in  FIG. 5 ) through solid heat conduction of the magnetic sheet  40 , the heat sink/magnetic shield plate  50 , the heat transfer conductive pattern on the front side  101  of the substrate  100 , the through-hole  112 , and the heat transfer conductive pattern  111  on the back side  102  of the substrate  100 . Moreover, since the temperature detection element  80  is provided on the back side  102  of the substrate  100 , the temperature detection element  80  does not interfere with the heat sink/magnetic shield plate  50 . Note that the thermistor wiring patterns  113 A and  113  B may be provided on the back side  102  of the substrate  100 , and the heat transfer conductive pattern  110  may be formed all over the front side  111  of the substrate  100 . 
     Note that the heat transfer conductive patterns  110  and  111  formed on the front side  101  and the back side  102  of the substrate  100  may not be connected via the through-holes  112  formed through the substrate  100 . For example, when the thickness of the substrate  100  is sufficiently small, heat may be transferred through an insulating material of the substrate  100 . 
     In this embodiment, as shown in  FIG. 3B , the substrate  100  has a mounting surface provided with a mounted component  106  in an area that extends from the area that faces the heat sink/magnetic shield plate  50 . The mounting surface is provided on the back side  102  opposite to the front side  101  that faces the heat sink/magnetic shield plate  50 . 
     Therefore, since only the planar coil  30 , the magnetic sheet  40 , and the heat sink/magnetic shield plate  50  protrude from the front side  101  of the substrate  100 , the primary coil and the secondary coil are easily disposed adjacently when performing non-contact power transmission. 
     3. Modification 
     Although only some embodiments of the invention have been described in detail above, those skilled in the art would readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of the invention. Accordingly, such modifications are intended to be included within the scope of the invention. Any term cited with a different term having a broader meaning or the same meaning at least once in the specification and the drawings can be replaced by the different term in any place in the specification and the drawings. 
     The above embodiments have been described taking an example relating to non-contact power transmission. Note that the invention may be similarly applied to non-contact signal transmission utilizing an electromagnetic induction principle. As shown in  FIG. 6 , the temperature detection element  80  may be provided on a front side  201  of a substrate  200 . In this case, a heat sink/magnetic shield plate  210  having a hole  211  (see  FIG. 6 ) may be used instead of the heat sink/magnetic shield plate  50  shown in  FIG. 2 . Since the hole  211  is formed corresponding to the air-core section  33  of the planar coil  30 , the heat sink effect does not deteriorate. Since the hole  211  is formed in the heat sink/magnetic shield plate  210 , the temperature detection element  80  does not interfere with the heat sink/magnetic shield plate  210  even if the temperature detection element  80  is provided on the front side  201  of the substrate  200 . In this case, it suffices that the heat transfer conductive pattern (omitted in  FIG. 6 ) be formed on the front side  201  of the substrate  100  in the area that faces the heat sink/magnetic shield plate  210 . A depression may be formed instead of the hole  211  formed in the heat sink/magnetic shield plate  210  insofar as interference with the temperature detection element  80  does not occur. The heat sink/magnetic shield plate  210  shown in  FIG. 6  may be used instead of the heat sink/magnetic shield plate  50  shown in  FIG. 2 . 
     A plurality of magnetic sheets  40  shown in  FIGS. 2 and 6  may be provided. When magnetic saturation occurs using only one magnetic sheet  40  when a large current flows through the planar coil  30  (e.g., when power is turned ON), a leakage flux can be reduced by providing a plurality of magnetic sheets  40 . 
     A planar coil is suitable as the coil in order to reduce the thickness of the coil unit. Note that the invention is not limited thereto. A planar coil formed by winding a coil wire around a planar core formed using a planar magnetic material may also be used. 
     Although only some embodiments of the invention have been described in detail above, those skilled in the art would readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of the invention. Accordingly, such modifications are intended to be included within the scope of the invention.