Patent Publication Number: US-6215386-B1

Title: Coil device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a coil device, and more specifically, it relates to a coil device provided with a plurality of coils at a single core. 
     2. Discussion of Background 
     A circuit which is achieved by connecting a plurality of coil devices being independent of one another is employed in various types of circuit apparatuses. For instance, a circuit having a common mode choke coil connected to the secondary winding of a transformer is employed in transmission apparatuses such as a LAN apparatus. 
     In a standard manufacturing process of a prior art circuit, a transformer and a common mode choke coil are manufactured separately and therefore mounted onto a circuit board separately. Not only does this require numerous mounting steps, but also limits the degree to which high density mounting is possible since a large area on the circuit board for mounting these parts is occupied. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a coil device that makes it possible to reduce the number of required parts by half. 
     It is a further object of the present invention to provide a coil device with which an improvement is achieved in the mounting density on a circuit board or the like. 
     It is a still further object of the present invention to provide a coil device achieving a high degree of magnetic efficiency. 
     It is a still further object of the present invention to provide a coil device with which it is possible to minimize the magnetic coupling among a plurality of coils. 
     In order to achieve the objects described above, the coil device according to the present invention includes a core, a first coil and a second coil. 
     The core is provided with at least four through holes. The through holes are provided roughly parallel to one another with a combination of two through holes among them constituting a first through hole pair and a combination of the remaining two through holes constituting a second through hole pair. These achieve a relationship whereby the center line passing through the centers of the through holes in the first through hole pair extends almost perpendicular to the center line passing through the centers of the through holes in the second through hole pair. The first coil passes through the first through hole pair whereas the second coil passes through the second through hole pair. 
     By adopting such a structure, it is possible to share the core between the first coil and the second coil to achieve a reduction in the number of required parts by half and to achieve an improvement in the mounting density on a circuit board or the like. Also, a toroidal—type closed magnetic circuit is formed by the core relative to the first coil and the second coil. As a result, the magnetic flux leaking to the outside is reduced and magnetic efficiency is improved. 
     With the through holes and the coils as described, it is possible to ensure that the magnetic flux generated by the current flowing to the first coil does not interlink with the second coil and that the magnetic flux generated by the current flowing to the second coil does not interlink with the first coil. Thus, it is possible to minimize the magnetic coupling between the first coil and the second coil. 
     The quantity of through holes, their positions and the like may be varied in a number of ways while ensuring that the requirements described above are satisfied. In addition, a number of different modes may be adopted in regard to the shape of the core member, its structure and the like. The present invention discloses examples of such variations and modes. 
     The first coil and the second coil each typically include two windings to constitute a transformer or a common mode choke coil. According to the present invention, the first coil and the second coil may be connected with each other on the core, or they may be connected outside, at a circuit board, a terminal plate or the like. 
     In another mode, the core may include a first core member and a second core member which are coupled with each other. By adopting this structure, magnetic characteristics that are suited for the individual coils, i.e., the first coil and the second coil, can be achieved. 
     According to the present invention, a coil refers to a component that is constituted by winding a wire and a winding refers to the wire member constituting the coil. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, structural features and advantages of the present invention are explained in further detailed by referring to the attached drawings. It is to be noted that the attached drawings are provided simply to illustrate examples. 
     FIG. 1 is a perspective of the coil device according to the present invention; 
     FIG. 2 is a perspective of a half section of the coil device shown in FIG. 1; 
     FIG. 3 is an electrical circuit diagram of the coil device shown in FIGS. 1 and 2; 
     FIG. 4 is an electrical circuit diagram of a structure employing the second coil as a common mode choke coil; 
     FIG. 5 is a perspective illustrating another example of the core member constituting the coil device according to the present invention; 
     FIG. 6 is a front view of another embodiment of the coil device according to the present invention; 
     FIG. 7 is an electrical circuit diagram of the coil device shown in FIG. 1; 
     FIG. 8 is a front view of yet another embodiment of the coil device according to the present invention; 
     FIG. 9 is a front view of yet another embodiment of the coil device according to the present invention; 
     FIG. 10 is a front view of yet another embodiment of the coil device according to the present invention; 
     FIG. 11 is an electrical circuit diagram of the coil device shown in FIG. 10; 
     FIG. 12 is a front view of yet another embodiment of the coil device according to the present invention; 
     FIG. 13 is a perspective of yet another embodiment of the coil device according to the present invention; 
     FIG. 14 is an exploded perspective of the coil device shown in FIG. 13; 
     FIG. 15 is a perspective of yet another embodiment of the coil device according to the present invention; 
     FIG. 16 is a side view of the coil device according to the present invention; 
     FIG. 17 is a front view of the coil device shown in FIG. 16; 
     FIG. 18 is a rear view of the coil device shown in FIG. 16; and 
     FIG. 19 is a side view of another embodiment of the coil device according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 to  3 , the coil device according to the present invention includes a core  1 , a first coil  2  and a second coil  3 . 
     The core  1  is provided with at least four through holes  41  to  44 . The through holes  41  to  44  are provided roughly parallel to one another. The through holes  41  to  44  are formed so that when a combination of two selected through holes among the through holes  41  to  44  constitutes a first through hole pair  41  and  42  and a combination of the remaining two through holes constitutes a second through hole pair  43  and  44 . A center line X passing through the centers of the first through hole pair  41  and  42  and a center line Y passing through the centers of the second through hole pair  43  and  44  extend almost perpendicular to each other. 
     The first coil  2  is wound by passing through the first through hole pair  41  and  42 , whereas the second coil  3  is wound by passing through the second through hole pair  43  and  44 . The number of turns of the first coil  2  and the second coil  3  is arbitrary. In addition, the directions in which their ends are lead out may be set freely. 
     By adopting the structure as described above, it is possible to share the core  1  between the first coil  2  and the second coil  3  to achieve a reduction in the number of required parts by half and to achieve an improvement in the mounting density on a circuit board or the like. 
     Also, a toroidal—type closed magnetic circuit is formed by the core  1  relative to the first coil  2  and the second coil  3 . As a result, the magnetic flux leaking to the outside is reduced and magnetic efficiency is improved. 
     By adopting the structure of the through holes  41  to  44 , as described above, it is possible to ensure that the interlinkage of the magnetic flux generated by the current flowing to the first coil  2  is minimized and at the same time, the interlinkage of the magnetic flux generated by the current flowing to the second coil  3  is minimized. Thus, it is possible to minimize the degree of magnetic coupling between the first coil  2  and the second coil  3 . The center lines X and Y do not need to extend exactly perpendicular to each other. They are only required to intersect each other at an angle at which the magnetic coupling of the first coil  2  and the second coil  3  is slight enough to be essentially disregarded. 
     In the embodiment illustrated in FIGS. 1 to  3 , the individual holes in the second through hole pair  43  and  44  are formed on the two sides of the center line X passing through the first through hole pair  41  and  42 . This placement of the through holes  43  and  44  minimizes the overall size of the coil device. 
     In addition, two ends of each of windings  21  and  22  constituting the first coil  2  are independent of each other. As a result, a transformer with the winding  21  constituting a primary winding and the winding  22  constituting a secondary winding, for instance, can be realized. By increasing the number of windings constituting the first coil  2 , a transformer achieving a required winding structure with a tertiary winding, a quaternary winding and the like, for instance, can be realized. 
     In the second coil  3 , too, the two ends of each of the windings  31  and  32  are independent of each other. Consequently, it is possible to achieve a coil  3  in which the windings  31  and  32  are independent of each other. A typical example of such a second coil  3  is a common mode choke coil. 
     FIG. 4 is an electrical circuit diagram illustrating a structure which utilizes the second coil  3  as a common mode choke coil. In this embodiment, the winding  21  and the winding  22  of the first coil  2  constitute a primary winding and a secondary winding respectively, one end of the winding  31  constituting the second coil  3  is connected to one end of the winding  22  (secondary winding) constituting the first coil  2  and one end of the winding  32  is connected to the other end of the winding  22  (secondary winding) constituting the first coil  2 . A signal input (IN) from the winding  21  (primary winding) of the first coil  2  is output (OUT) through the other end of the winding  31  and the other end of the winding  32 . 
     Referring to FIG. 5, the core  1  is provided with a coil guide groove  40  at an end surface  10  at which the through holes  41  to  44  open. The first coil  2  and the second coil  3  can be wound around through the coil guide groove  40  at the end surface where the through holes  41  to  44  open. Thus, miniaturization can be achieved by ensuring that the first coil  2  and the second coil  3  do not project out while protecting the first coil  2  and second coil  3 . The coil guide groove  40  should be formed by ensuring that its bottom surface is at a position lower than the end surface  10  and connects the through holes  41  and  42  or the through holes  43  and  44 . The shape of the coil guide groove  40  is not restricted to the example shown in the figure. 
     The core  1  may be constituted of an insulating sintered magnetic substance such as ferrite. The first coil  2  and the second coil  3  can be directly wound around the core  1  constituted of such an insulating sintered magnetic substance. If the core  1  is constituted of a material having a degree of electrical conductivity that cannot be disregarded in terms of electrical insulation of the first coil  2  and the second coil  3 , an insulating film should be formed at, at least, the surface areas of the core that come in contact with the first coil  2  and the second coil  3 , including the inner surfaces of the through holes  41  to  44 . The insulating film may be constituted of an insulating resin film or an inorganic insulating film such as glass. 
     Referring to FIGS. 6 and 7, the core  1  is provided with a groove  10  extending along the direction in which the through holes  41  to  44  are provided, at the outer surface of the core. The two windings  31  and  32  constituting the second coil  3  are each connected to an end of the winding  22  constituting the first coil  2  through the groove  10 . A signal input (IN) through the winding  21  (primary winding) of the first coil  2  is output (OUT) through the other end of the winding  31  and the other end of the winding  32 . 
     Referring to FIG. 8, wherein the same reference numbers are assigned to components identical to those illustrated in FIGS. 1 to  3 , the external shape of the core  1  is rectangular, with the first through hole pair  41  and  42  and the second through hole pair  43  and  44  provided along the directions of the diagonal lines. This embodiment, too, achieves advantages similar to those described earlier in reference to FIGS. 1 to  3 . 
     Referring to FIG. 9, wherein the same reference numbers are assigned to components identical to those illustrated in FIGS. 1 to  8 , the second through hole pair  43  and  44  is provided on one side of the center line X of the first through hole pair  41  and  42 . This embodiment, too, achieves advantages similar to those described earlier in reference to FIGS. 1 to  3 . 
     Referring to FIG. 10, wherein the same reference numbers are assigned to components identical to those illustrated in FIGS. 1 to  8 , a plurality of first through hole pairs ( 411  and  412 ) and ( 421  and  422 ) are provided. A first coil  210  is provided at the first through hole pair  411  and  412 , and a first coil  220  is provided at the first through hole pair  421  and  422 . The first coil  210  includes a plurality of windings  211  and  212  that are independent of the each other, whereas the first coil  220  includes a plurality of windings  221  and  222  that are independent of each other. 
     A center line X 1  passing through the centers of the holes in the first hole pair  411  and  412  extends almost perpendicular to the center line Y passing through the centers of the holes in the second through hole pair  43  and  44 . A center line X 2  passing through the centers of the holes in the first hole pair  421  and  422 , too, extends almost perpendicular to the center line Y passing through the centers of the holes in the second through hole pair  43  and  44 . The first through hole pairs ( 411  and  412 ) and ( 421  and  422 ) are formed over a distance dl from each other along the direction in which the center line Y passing through the centers of the holes in the second through hole pair  43  and  44  provided for the second coil  3  extends. 
     Referring to FIG. 11, a transformer having two coils  210  and  220  is formed in the embodiment shown in FIG.  10 . At the coil  210 , the winding  211  constitutes a primary winding and the winding  212  constitutes a secondary winding. At the coil  220 , the winding  221  constitutes a primary winding and the winding  222  constitutes a secondary winding. 
     If the second coil  3  constitutes a common mode choke coil, its windings  31  and  32  are connected to the secondary winding constituted of the winding  212  or the secondary winding constituted of the winding  222  at one end. 
     Referring to FIG. 12, wherein the same reference numbers are assigned to components identical to those illustrated in FIG. 10, the first through hole pairs ( 411  and  412 ) and ( 421  and  422 ) are provided on the center line X, which extends almost perpendicular to the center line Y passing through the centers of the holes in the second through hole pair  43  and  44  provided for the second coil  3 . 
     Referring to FIGS. 13 and 14, the core  1  includes a first core member  11  and a second core member  12 . The first core member  11  and the second core member  12  are coupled through surface contact, with the first through hole pair  41  and  42  for the first coil  2  provided at the coupling surface. 
     At the coupling surface, the through hole  44  in the second through hole pair  43  and  44  for the second coil  3  is also provided. The through hole  43  alone is provided at the second core member  12 . By adopting this structure, the materials to constitute the first core member  11  and second core number  12  may be selected independently of each other to achieve magnetic characteristics that suit the individual coils, i.e., the first coil  2  and the second coil  3 . For instance, the first core member  11  may be constituted by employing a material achieving a high initial magnetic permeability, with the second core member  12  constituted of a material with an initial magnetic permeability lower than that of the material constituting the first core member  11 . 
     Referring to FIG. 15, the first core member  11  and the second core member  12  are coupled with each other through surface contact. The first through hole pair  41  and  42  provided for the first coil  2  and the through hole  44  provided for the second coil  3  are provided at the first core member  11 . The through hole  43  in the second through hole pair  43  and  44  is provided at the second core member  12 . Through this structure, too, advantages similar to those explained earlier in reference to FIGS. 13 and 14 are achieved. 
     Referring to FIGS. 16 to  18 , the coil device includes a plurality of terminal electrodes ( 51  to  54 ) and ( 61  to  64 ). The four ends of the windings  21  and  22  constituting the first coil  2  are respectively connected to the terminal electrodes  51  to  54 . The four ends of the windings  31  and  32  constituting the second coil  3  are respectively connected to the terminal electrodes  61  to  64 . The terminal electrodes ( 51  to  54 ) and ( 61  to  64 ) are utilized to affix the coil device at a conductor pattern provided at a board through a means such as soldering when mounting the coil device at the board. In the embodiment, the terminal electrodes ( 51  to  54 ) and ( 61  to  64 ) are formed at appropriate positions at the lower surface or the like of the core  1 , achieving electrical insulation. Such terminal electrodes ( 51  to  54 ) and ( 61  to  64 ) may be formed by means such as plating or baking of coated conductive paste or the like. 
     Referring to FIG. 19, the coil device is provided with an insulating support body  7 . The core  1  is mounted on one surface of the insulating support body  7  through bonding or by a means of mechanical coupling. The terminal electrodes ( 51  to  54 ) and ( 61  to  64 ) are mounted at the insulating support body  7 . The four ends of the windings  21  and  22  constituting the first coil  2  are respectively connected to the terminal electrodes  51  to  54 . The four ends of the windings  31  and  32  constituting the second coil  3  are respectively connected to the terminal electrodes  61  to  64 . 
     While no further explanation or illustration is presented, it is obvious that there may be a number of variations of the present invention achieved by combining the individual embodiments.