Patent Publication Number: US-8120458-B2

Title: Ferrite core and transformer using the same

Description:
CROSS-REFERENCE TO PRIORITY APPLICATIONS 
     The present application is a divisional of U.S. application Ser. No. 11/410,065 filed on Apr. 25, 2006, and claims priority to JP 2005-132812 filed on Apr. 28, 2005, JP 2005-275257 filed on Sep. 22, 2005, JP 2005-285490 filed on Sep. 29, 2005, and JP 2005-370829 filed on Dec. 22, 2005, the entire contents of each of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a ferrite core and a bobbin corresponding the ferrite core used in a coiled component for various electronic equipments, and to a transformer including the ferrite core and the bobbin. 
     Used in a coiled component mounted in office machinery and appliances, a ferrite core is known in the related art, which includes an end face portion, a pair of outer legs protruding from both sides of the end face portion, and a center leg protruding from the end face portion between the outer legs. The conventional ferrite core&#39;s center leg has a circular, polygonal, elliptical, or oval cross section, and an inductor, such as a choke coil, or a transformer is configured by inserting the center leg into a wound body with wire wound of a bobbin. 
     A ferrite core  40  for a transformer is disclosed in Patent Document 1 and 2, which has an elliptical or oval cross section in order to achieve a small-sized and thin transformer, as shown in  FIG. 21 . In  FIG. 21 , a reference numeral is given to each part as follows, outer legs  42  of the core  40 , a bobbin  43 , a wound body  44  of the bobbin  43 , first and second winding wire terminal blocks  45  and  46  of the bobbin, respectively, a winding wire  47  around the wound body  44 , a first terminal  49  connected with the first winding wire, a second terminal  50  connected with the second winding wire, first and second ports  51 ,  52 , respectively.
     [Patent Document 1] JP-UM-B-3-53462   [Patent Document 2] JP-UM-A-5-87918   

     A center leg in a conventional ferrite core has a circular, polygonal, elliptical, or oval cross section. For example, when the center leg&#39; cross section is elliptical as shown in  FIG. 23 , magnetic leakage flux φ 1  and φ 2  is uniformly generated by current through a wire (not shown) at both ends of a center leg  41  in a core, reference numerals  42  represents an outer leg. 
     The magnetic leakage flux φ 1  and φ 2  generated at both sides of the conventional core  40  is uniform and affects an adjacent circuit component by noise. In particular, a flyback transformer in electronic equipment has a gap between the center legs of the core, therefore, a large amount of magnetic leakage flux is generated from the gap. 
     Accordingly, excess current is generated in a conductor composing a terminal or signal wire of the adjacent circuit component, thus it prevents improving properties of the circuit component. A circuit component affected by the noise is required to be positioned apart from transformer, as a result, it is difficult to manufacture a small-sized electric and electronic equipment, such as a power device, using the circuit component. Further, a shield, such as a shield wire, a shield plate, or a shield cover, is needed for preventing the magnetic leakage flux, thereby increasing cost. 
     As shown in  FIG. 21 , when the center leg  41  has an oval or elliptical cross section, since a distance between the center leg  41  and the outer legs  42  is constant throughout the periphery of the center leg, a distance G 7  at the first winding wire terminal block  45  is the same as a distance G 8  at the second winding wire terminal block  46  between the left and right outer legs (G 7 =G 8 ). 
     In recent years, as electronic equipment, such as appliances, has had multiple functions, second winding wires involved increases and ports for the second winding wires led to the second winding wire terminal block  46  in the terminal  50  connected with the second winding wires increases. In  FIG. 13 , the ports of the second winding wire  52  are led to the left and right end portions of the second winding wire terminal block  46 , as a result, an insulating distance d between the second port and the outer leg  42  of the core  40  is not sufficient. Accordingly, the second port  52  at the outer leg  42  is coated with a tube or tape for insulation, thus the structure is complicated for leading the ports. It takes much time to connect the winding wire to the terminal  50  in the port, therefore, working efficiency is reduced. 
     Considering the above-mentioned problem, as shown in  FIG. 14 , a distance G 8  between the outer legs  42  at the second winding wire terminal block  46  is set larger than a distance G 7  between the outer legs  42  at the first winding wire terminal block  45  (G 7 &lt;G 8 ). However, since the distance between the outer leg  42  and the center leg  41  is not constant, magnetic flux tends to concentrate at an area where the center leg  41  and the outer leg  42  are relatively close. As a result, magnetic saturation is likely to occur, and in a converter transformer, its overlapping property deteriorates under overlapping condition of direct current and alternating current. 
     In the above example in the related art, a vertical-type transformer is disclosed, in which the center leg  41  or outer legs  42  vertically protrudes from a base plate, however, the above-mentioned problems also appear in a horizontal-type transformer in which a ferrite core is mounted parallel to the base plate. 
     SUMMARY OF THE INVENTION 
     Considering the above problems, according to the present invention, it is an object to provide a ferrite core in which a circuit component easily affected by magnetic leakage flux is positioned close to the ferrite core composing a coiled component and electric or electronic equipment is small-sized, and a transformer using the ferrite core. 
     Further, it is an object of the present invention to provide a ferrite core preventing partial concentration of magnetic flux and deterioration of properties by setting a distance at one side between outer legs larger than a distance at the other side and surely insulating winding wire from the outer legs, thereby small-sized. It is also an object to provide a transformer using the ferrite core. 
     According to the present invention, a ferrite core includes an end face portion, a pair of outer legs protruding from both sides of the end face portion, and a center leg protruding from the end face portion between the outer legs. 
     A width close to one end of the center leg in a perpendicular direction to a facing direction of the outer legs is set smaller than a width close to the other end. 
     A ferrite core according to the invention has a substantially egg-shaped cross section. 
     A transformer according to the invention includes the ferrite core. 
     According to the present invention, a ferrite core includes an end face portion, a pair of outer legs protruding from both sides of the end face portion, and a center leg protruding from the end face portion between the outer legs. 
     In the ferrite core, an X-axis direction is defined as a direction when the position of each end of the outer legs  3  and the center leg  4  are in a line and a Y-axis direction is defined as a direction perpendicular to the X-axis. Assuming the origin is a center of the Y-axis direction, the center leg has different widths W 1  and W 2  in the X-axis direction, which are measured at two positions apart from the origin at the same distance in two directions, respectively, and is asymmetric about the X-axis. A distance between the outer legs at a wide side of the center leg in the X-axis direction is larger than a distance at the opposite side. 
     The center leg of the ferrite core preferably has an egg-shaped or substantially U-shaped cross section. 
     According to the invention, a transformer (vertical-type transformer) includes a pair of ferrite cores having egg-shaped cross section and a bobbin for combining the ferrite cores. The bobbin has a tubular wound body having egg-shaped cross-section into which the center legs are inserted and having winding wires around itself. First and second winding wire terminals are mounted opposite at a narrow side and a wide side of one longitudinal end of the wound body of the bobbin, respectively. The ferrite cores are combined with the bobbin by inserting their center legs into the wound body and interposing the outer legs of one of the ferrite cores between the first and second winding wire terminals. 
     Further, a transformer (horizontal-type transformer) according to the invention includes a pair of ferrite cores having U-shaped cross-section and a bobbin for combining the ferrite cores. The bobbin has a tubular wound body having U-shaped cross-section into which the center legs are inserted and having winding wires wound around it. First and second winding wire terminals are mounted at a narrow side and a wide side of both longitudinal ends of the wound body of the bobbin, respectively. The ferrite cores are combined with the bobbin by inserting their center legs into the wound body and positioning a wide side of the outer legs of one of the ferrite cores at the first winding wire terminal block and a wide side of the outer legs of the other ferrite core at the second winding wire terminal block. 
     Additionally, a concave portion capable of discriminating a direction of the ferrite core is formed in at least one of an opposing side end face and a lateral face of a protruded face of the center leg and outer leg of the ferrite core, or a R face, a C face or a stepped portion capable of discriminating the direction of the ferrite core is formed together with the concave portion or is independently formed in a corner capable of viewing from a portion of the end face of the ferrite core. 
     In a ferrite core according to the invention, since a width close to one end of the center leg in a perpendicular direction to a facing direction of the outer legs is set smaller than a width close to the other end, magnetic leakage flux toward the outside from the narrow end portion reduces as compared to the other end portion and a circuit component can be adjacently positioned at the narrow end portion. Therefore, electric and electronic equipment can be small-sized by using a coiled component combined with the ferrite core. Also, a shield for protect the adjacent positioned circuit product from the magnetic leakage flux is not necessary and the equipment can be small-sized. 
     Since a transformer according to the invention includes the ferrite core according to the invention, a circuit component is positioned close to the narrow end portion of the center leg in the ferrite core in the transformer. Accordingly, electric and electronic equipment using the transformer can be small-sized and shield is not necessary, furthermore, the equipment can be more compact and the cost can be remarkably reduced. 
     According to the ferrite core, the center leg has an egg-shaped or U-shaped cross section, which is asymmetric about a line passing the origin on the Y-axis of the center leg in a facing direction of the outer legs. Therefore, a distance between the center leg and outer leg at a wide side of the center leg in the X-direction is larger than a distance between them at a narrow side. Even though the distance between the center leg and the outer leg at the wide side of the center leg is set larger than the distance at the other side, the distance is constant throughout the periphery of the center leg. Accordingly, even if the ferrite core is employed in a transformer, magnetic saturation due to partial concentration of magnetic flux does not occur and it maintains properties and can be small-sized. 
     Since at least one distance between the outer legs is large, ports led from the distance increase. Also, a twist wire is available and the number and diameter of the wire can be increased, thereby saving copper and providing a transformer having high efficiency and outputting high current. Furthermore, the increased port, the thick wire or the twist wire is led from the wide distance between the outer legs, thus a tube or a tape is not necessary for insulating between the winding pots and outer legs. Working efficiency is also improved. 
     In the vertical-type transformer according to the invention, the second winding wire terminal block is mounted at the wide side between the outer legs, therefore, a wide area for leading a great number of the second ports is defined. As described above, the magnetic saturation does not occur and the transformer maintains its properties and can be small-sized. Also, the transformer is capable of increasing output capacitance by using a heavy wire and a twist wire for the second winding wire and responding to the demand for a new electronic equipment by increasing the number of the second winding wire, and leading the port with ease. 
     In the horizontal-type transformer, an area for leading the ports in both of the first and second winding wire terminal blocks, therefore, the same effect as described above is obtained and the first port is surely insulated from the outer legs, as well as the second port. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of an embodiment of a core according to the invention 
         FIG. 2  is a front view of  FIG. 1 . 
         FIG. 3  is a front view showing an embodiment of a transformer including the core in  FIGS. 1 and 2 . 
         FIG. 4  is a side view of the transformer in  FIG. 3 . 
         FIG. 5  is a rear view of the transformer in  FIG. 3 . 
         FIG. 6  is a side view showing an arrangement of the transformer in  FIGS. 3 to 5  on a printed board. 
         FIGS. 7A to 7D  are plan views of another embodiment of the center leg in the core according to the invention. 
         FIGS. 8A and 8B  are plan views of another embodiment of the outer leg in the core according to the invention. 
         FIG. 9  is a plan view showing an embodiment of a core according to the invention. 
         FIG. 10  is a side view of  FIG. 9 . 
         FIG. 11  a front view showing an embodiment of a vertical-type transformer including the core of  FIGS. 9 and 10 . 
         FIG. 12  is a side view of the transformer in  FIG. 11 . 
         FIG. 13  is a rear view of the transformer in  FIG. 11 . 
         FIG. 14  is a cross-sectional view of the transformer in  FIG. 11 . 
         FIG. 15  is a plan view showing another embodiment of a core according to the invention. 
         FIG. 16  is a plan view showing another embodiment of a core according to the invention. 
         FIG. 17  is a front view of a bobbin for horizontal-type transformer using the core in  FIG. 15 . 
         FIG. 18  is a plan view showing an embodiment of a horizontal-type transformer using the core in  FIG. 16  and the bobbin in  FIG. 17 . 
         FIG. 19  is a side view of the transformer in  FIG. 18 . 
         FIG. 20  is a bottom view of the transformer in  FIG. 19 . 
         FIG. 21  is a cross-sectional view of a transformer in the related art. 
         FIG. 22  is a plan view showing a modification of a core in the related art. 
         FIG. 23  is a plan view showing a core in the related art. 
         FIG. 24  is a front view showing an embodiment of a bobbin according to the present invention. 
         FIG. 25  is a side view of  FIG. 24 . 
         FIG. 26  is a rear view of  FIG. 24 . 
         FIG. 27  is a cross-section view taken along a line E-E in  FIG. 25 . 
         FIG. 28  is a front view of a transformer using the bobbins shown in  FIGS. 24 to 26 . 
         FIG. 29  is a side view of the transformer of  FIG. 28 . 
         FIG. 30  is a side view showing an operating state in which wires are wound on the bobbin. 
         FIG. 31  is a cross-section view taken along a line F-F in  FIG. 30 . 
         FIG. 32  is a cross-section view showing another embodiment of the bobbin according to the present invention. 
         FIG. 33  is a cross-section view showing another embodiment of the bobbin according to the present invention. 
         FIG. 34  is a cross-section view showing another embodiment of the bobbin according to the present invention. 
         FIG. 35  is a cross-section view showing another embodiment of the bobbin according to the present invention. 
         FIG. 36  is a cross-section view showing another embodiment of the bobbin according to the present invention. 
         FIG. 37  is a cross-section view showing another embodiment of the bobbin according to the present invention. 
         FIG. 38  is a rear view showing another embodiment of the bobbin according to the present invention. 
         FIG. 39  is a side view of the bobbin of  FIG. 38 . 
         FIG. 40  is a plane view showing an embodiment of a core according to the present invention. 
         FIG. 41  is a side view of  FIG. 40 . 
         FIG. 42  is a bottom view of  FIG. 40 . 
         FIG. 43  is a front view of a vertical transformer using the core according to the embodiments shown in  FIGS. 40 to 42 . 
         FIG. 44  is a side view of the transformer of  FIG. 43 . 
         FIG. 45  is a rear view of the transformer of  FIG. 44 . 
         FIG. 46  is a view showing a magnetic flux distribution in the core according to the embodiment. 
         FIGS. 47A to 47C  are views showing a cross-sectional shape of a concave portion. 
         FIG. 48  is a bottom view showing another embodiment of the core according to the present invention. 
         FIG. 49  is a bottom view showing another embodiment of the core according to the present invention. 
         FIG. 50  is a bottom view showing another embodiment of the core according to the present invention. 
         FIG. 51  is a bottom view showing another embodiment of the core according to the present invention. 
         FIGS. 52A to 52C  are views showing examples of the cross-section shape of a directional recognition portion provided at a corner of the core according to the present invention. 
         FIG. 53  is a bottom view showing another embodiment of the core according to the present invention. 
         FIG. 54  is a front view of a horizontal transformer using the core according to the embodiments shown in  FIGS. 40 to 42 . 
         FIG. 55  is a side view of the transformer of  FIG. 54 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       FIG. 1  is a plan view showing an embodiment of a ferrite core according to the invention and  FIG. 2  is a front view of the ferrite core. The ferrite core  1  has an end face portion  2 , a pair of outer legs  3  protruding from the end face portion  2 , and a center leg protruding from the end face portion  2  between the pair of outer legs  3 . An X-axis direction is defined as a direction when the position of each end of the outer and center legs  3  and  4  are in a line and a Y-axis direction is defined as a direction perpendicular to the X-axis. In both end portions in the Y-axis direction, a width W 1  close to an end portion  4   a  (a width apart from an end portion at the upper side at a predetermined distance L 1  in  FIG. 1 ) is smaller than a width W 2  apart from the other end portion  4   b  at the same distance L 1  (W 1 &lt;W 2 ). In this embodiment according to the invention, the center leg  4  has an egg-shaped cross section. The outer legs  3  have a constant width in the Y-axis direction. 
       FIG. 3  is a front view showing an embodiment of a vertical-type transformer including a ferrite core  1 , and  FIGS. 4 and 5  are a side view and a rear view, respectively. Reference numerals  5 ,  6 ,  7 ,  8 , and  9  represent a bobbin, a wound body, a first winding wire terminal block, a second winding wire terminal block, and a flange at top of the wound body  6 , respectively. A reference numeral  10  indicates a winding wire around the wound body  6  having a tape on its periphery, and includes first and second winding wires. Reference numerals  11 ,  12 ,  13 , and  14  represent a first port, a second port, a first winding wire terminal fixed to the first winding wire terminal block  7 , and a second winding wire terminal fixed to the second winding wire terminal block  8 , respectively. 
     The center leg  4  is inserted into the wound body  6 , which has an egg-shaped cross section corresponding to the shape of the center leg  4 . As shown in  FIGS. 3 to 5 , the first and second winding wire terminal blocks  7  and  8  are mounted at one end of the wound body  6  in its axis direction. The second winding wire terminal block is provided at the wide end portion  4   b  of the center leg  4  in the ferrite core  1  and the first winding wire terminal  7  is provided at the narrow end portion  4   a.    
     In combination of the bobbins  5  and the cores  1 , each center leg  4  of the pair of cores  1  is inserted into the wound body  6 , outer legs  3  of one core  1  are interposed between the first and second winding wire terminal blocks  7  and  8 , and the combined cores  1  are fixed to each other by taping their peripheries or using an adhesive. 
     According to this configuration, as shown in  FIG. 1 , in magnetic leakage flux in the core  11  due to the current through a winding wire  10 , magnetic leakage flux φ 1  at the narrow end portion  4   a  is less than magnetic leakage flux φ 2  at the other end portion. 
     As shown in  FIG. 6 , when a transformer  21  including the ferrite core  1  and other circuit components  22  and  23  are mounted on a printed board  20 , the circuit component  22 , such as an integrated circuit element, relatively easily affected by the magnetic leakage flux is positioned at the narrow end portion  4   a  of the center leg  4  and the circuit component  23  relatively hardly affected by the magnetic leakage flux is positioned at the wide end portion  4   b , thereby reducing the effect by the magnetic leakage flux φ 1  and φ 2 . Electric and electronic equipment such as a switching power including the printed board  20 , the transformer  21 , or the circuit component  22  and  23  is small-sized by positioning the circuit components  22  and  23  close to the transformer  21 . Also, a shield is not necessary for the circuit component  22 , thereby saving cost for the electric and electronic equipment in addition to small-sizing. 
     In particular, in a wiring pattern or an integrated circuit element involved with a video and audio signal used in digital equipment, it is preferred to reduce noise effect as little as possible. In this case, the noise effect is reduced by positioning the wiring pattern or the integrated circuit element close to the circuit component  22 . When the transformer is positioned closed to a hard disc device or optical pick-up device, the noise effect due to the transformer may be reduced by positioning the devices at an area where the magnetic leakage flux φ 1  is generated, that is, magnetic leakage flux is less than the other. 
       FIG. 7  is a plan view of another embodiment of a center leg.  FIG. 7A  shows a cross section of the center leg  40  where a wide end portion  40   b  is cut in a straight line and a narrow end portion  40   a  is not.  FIG. 7B  shows a cross section of the center leg  41  where a narrow end portion  41   a  is a mountain shape and a wide end portion  41   b  is polygonal. In  FIG. 7C , a narrow end portion  42   a  of a center leg  42  is an arc having small radius of curvature and a wide end portion  42   b  is an arc having large radius of curvature. In  FIG. 7D , a center leg  43  has a triangular cross section in which the apexes are rounded and the angular point  43  is a narrow end portion and the base  43   b  is a wide end portion. In each case, the same effects as the previous embodiment including small-sizing are obtained by positioning the circuit component close. 
       FIG. 8  is a plan view showing another embodiment of an outer leg in a core according to the invention. The outer leg composes a ferrite core together with the center legs  4  and  40  to  43  shown in  FIGS. 1 and 7 . In  FIG. 8A , a distance W 3  between ends of an outer leg  30 , i.e. ends  30   a  corresponding to the narrow end portion of the center leg  4  (or one of the center legs  40  to  43 ) is smaller than a distance W 4  between the other ends (W 3 &lt;W 4 ). In  FIG. 8B , a distance between mid-portion  31   a  of the outer legs  31  is larger than a distance W 6  between both end portions  31   b  (W 5 &gt;W 6 ). The magnetic leakage flux φ 1 , in particular, is reduced and more small-sized electric and electronic equipment having circuit component  22  close to another component is achieved by configuring such that the distance between the end portions  30   a  of the outer legs  30  corresponding to the narrow end portion of a center leg, as shown in  FIG. 8A . 
     In applying the present invention, the cross section of the center legs  4  and  40  to  43  may be positioned at an angle about Y-axis and the end portions of the center legs  4  and  40  to  43  may have the same shape as the end face  2   a  and  2   b  of the end face portion. 
     Second Embodiment 
       FIG. 9  is a plan view showing an embodiment of a ferrite core according to the invention and  FIG. 10  is a side view of the ferrite core. The ferrite core  101  has an end face portion  102 , a pair of outer legs  103  protruding from the end face portion  102 , and a center leg protruding from the end face portion  102  between the pair of outer legs  103 . An X-axis direction is defined as a direction when the position of each end of the outer legs  103  and the center leg  104  are in a line and a Y-axis direction is defined as a direction perpendicular to the X-axis. Assuming the origin O is a center of the Y-axis direction, the center leg  104  has different widths W 1  and W 2  (W 1 &lt;W 2 ) in the X-axis direction, which are measured at two positions apart from the origin at the same distances +Δy and −Δy in two directions, respectively, and an egg-shaped cross section that is asymmetric about the X-axis. Accordingly, a distance G 2  between the outer legs  103  at a wide side of the center leg  104  in the X-axis direction is larger than a distance G 1  at the opposite side (G 1 &lt;G 2 ). 
     In the case the cross section of the center leg  104  is asymmetric as described above, even though the distance G 2  between the outer legs  103  at the wide side of the center leg is larger than the distance G 1  at the opposite side, the distance between the center leg  104  and outer legs  103  may be set constant throughout the periphery of the center leg. Therefore, even if the ferrite core is employed in a transformer, magnetic saturation due to partial concentration of magnetic flux does not occur and it maintains properties and is small-sized. As shown in  FIG. 21 , a width at the wide side between the outer legs  103  can be reduced as compared to when a center leg  121  has an oval or elliptical cross section, therefore, the width of the core  101  in X-axis direction can be small and small-sized core is achieved. 
     Since at least one distance, i.e. the distance G 2  between at least one ends of the outer legs  103  is larger than the other, the number of ports led from the distance may be increased. A twist wire is available and the number and diameter of wire may be increased, thereby saving copper and providing a transformer having high efficiency and outputting high current. As described above, the increased port, the thick wire or the twist wire is led from the wide distance between the outer legs, thus insulation is easily achieved. 
       FIG. 11  is a front view showing an embodiment of a vertical-type transformer including a ferrite core  1 , and  FIGS. 12 ,  13 , and  14  are a side view, a rear view, and a cross-sectional view of the embodiment in  FIG. 11 , respectively. Reference numerals  105 ,  106 ,  107 ,  108 , and  109  represent a bobbin, a wound body, a first winding wire terminal block, a second winding wire terminal block, and a flange at the top of the wound body  106 , respectively. A reference numeral  110  indicates a winding wire that is wound around the wound body  106 , has a tape on its periphery, and includes first and second winding wires. Reference numerals  111 ,  112 ,  113 , and  114  represent a first port, a second port, a first winding wire terminal fixed to the first winding wire terminal block  107 , and a second winding wire terminal fixed to the second winding wire terminal block  108 , respectively. 
     As shown in  FIG. 14 , the center leg  104  is inserted into the wound body  106 , which has an asymmetric egg-shaped cross section corresponding to the shape of the center leg  104 . As shown in  FIGS. 11 to 13 , the first and second winding wire terminal blocks  107  and  108  are mounted at one end of the wound body  106  in its axis direction. As shown in  FIG. 14 , the second winding wire terminal block  108  is positioned at the wide side of the wound body  106  and the first winding wire terminal block  107  is positioned at the opposite narrow side. 
     In combination of the bobbin  105  and the cores  101 , each center leg  104  of the pair of cores  101  is inserted into the wound body  106 , outer legs  103  of one core  1  are interposed between the first and second winding wire terminal blocks  107  and  108 , and the combined cores  101  are fixed to each other by taping their peripheries or an adhesive. 
     According to this configuration, as shown in  FIG. 14 , the width G 2  between the outer legs  103  at a leading side of the second port  112  including a large number of winding wires is larger than the width G 1  between the outer legs  103  at a leading side of the first port  111 . Therefore, a width ‘a’ of a leading portion  115  at the first winding wire terminal block is smaller than a width ‘b’ of a leading portion  116  at the second winding wire terminal block  108  (a&lt;b), thus the second port  112  is easily led. Further, an insulating distance ‘d’ between an outermost second port  112  and the outer leg  103  is also sufficiently defined like an insulating distance ‘c’ between the first port  111  and the outer leg  103 . Accordingly, a tube or tape is not necessary for insulating between the outermost second port  112  and the outer leg  103 , which facilitates connection with the second winding wire terminal  114  for second port  112 . 
     The leading portion  116  for the second port  112  is wide, thus the second port  112  increases. A twist wire is available and the number and diameter of the second winding wire may be increased, thereby saving copper and providing a transformer having high efficiency and outputting high current. 
       FIG. 15  is a plan view of another embodiment of a core according to the invention. In this embodiment, a center leg  104 A protrudes from an end face  102 A and has substantially triangular cross section. Similar to the previous embodiment, a distance G 4  between the outer legs  103 A at one side is wider than a distance G 3  at the other side, thereby achieving the same effect. 
       FIG. 16  is a plan view of another embodiment of a core according to the invention. In this embodiment, a core  120  is preferably available to a horizontal-type transformer and a center leg  121  is positioned at one side of an end face portion  122 . In the embodiment, an X-axis direction is defined as a direction when the position of each end of the outer legs  123  and the center leg  121  are in a line and a Y-axis direction is defined as a direction perpendicular to the X-axis. Assuming the origin O is a center of the Y-axis direction, the center leg  121  has different widths W 3  and W 4  (W 3 &lt;W 4 ) in the X-axis direction, which are measured at two positions apart from the origin at the same distances +Δy and −Δy in opposite directions, respectively, and a semicircular cross section that is asymmetric about the X-axis. Accordingly, a distance G 6  between the outer legs  123  at the wide side of the center leg  121  in the X-axis direction is larger than a distance G 5  at the opposite side (G 5 &lt;G 6 ). 
       FIG. 17  is a front view of a bobbin that is combined with the core  120  in  FIG. 15  and used in a horizontal-type transformer.  FIG. 18  is a plan view of a horizontal-type transformer including a bobbin  124  and the core  120  of  FIG. 15 , and  FIGS. 19 and 20  are a side view and a bottom view of the transformer, respectively. The horizontal-type transformer complies with requisition for a low unit, therefore, the bobbin  124  has a tubular wound body  126  into which the center leg  121  is inserted and winding wire  125  is wound around the bobbin, and the wound body  126  has an U-shaped cross section corresponding to the center leg  121 . A first winding wire terminal block  128  having a first winding wire terminal  127  at the wide side of the wound body  126  and a second winding wire terminal block  139  having a second winding wire terminal  129  are provided at both longitudinal ends of the wound body  126  of the bobbin  124 . While the center legs  121  of the pair of cores  120  are inserted into the wound body  126 , a wide side of two outer legs  123  of one core  120  is positioned at the first winding wire terminal block  128  and a wider side of two outer legs  123  of the other core  120  is positioned at the first winding wire terminal block  130 , whereby the cores  120  are combined with the bobbin  124 . The cores  120  may be fixed to each other by taping around them or using an adhesive. 
     In the above embodiment, leading portions of the ports  131  and  132  are sufficiently wide in the first and second winding wire terminal blocks  128  and  130 , because the distance G 6  defining a leading portion for the second port  132  between the outer legs at the upper portion of the figure is larger than the distance G 5  defining a leading portion for the first port  131  at the lower portion. In this case, the distance between the center leg  121  and the outer legs  123  are also constant throughout the center leg&#39;s periphery. As a result, in addition to preventing a magnetic saturation and deterioration of the properties and small-size, increasing output capacitance by a heavy second winding and a twist wire are achievable, or responding to the demand for a new one and leading of the port is utilized by increasing the number of the second winding wire. 
     Also, in addition to the second winding wire, in the case of increasing the number of the first winding wire, the same effects as described above are achieved and a transformer having various output voltages are easily achieved. 
     Third Embodiment 
       FIGS. 24 to 26  are a front view, a side view, and a rear view showing a first embodiment of a bobbin according to the present invention, respectively, and  FIG. 27  is a cross-section view taken along a line E-E in  FIG. 26 . These embodiments show a vertical type transformer in which the terminal blocks  207  and  208  mounted a first side terminal  205  and second side terminal  206  on only one side guard  203  of the guards  203  and  204  are provided. The guards  203  and  204  are formed in both ends of a hoisting drum  202  which winds a coil on a bobbin  1 . 
     In  FIG. 27 , O indicates a vertical and horizontal center point of the hoisting drum  202 . Here, a Y-axis is the center line of an opposing direction of terminal blocks  207  and  208 , in a cross-section of a direction vertical to the core of a cavity of the hoisting drum  202 , and X-axis is the center line of the direction vertical to the opposing direction of the terminal blocks in the cross-section. At this time, in this embodiment, it is formed such that the cross-sections of one region  210  and the other region  211  divided by the X-axis are asymmetrical. In the embodiment, the cross-section of the cavity (also, periphery thereof) of the hoisting drum  202  is formed into an oval-like shape. 
       FIG. 28  is a front view showing an example of the transformer which is configured using the bobbin, and  FIG. 29  is a side view of  FIG. 28 . Such transformer is to use two E type cores  212  made of a ferrite material. The cores  212  include end faces  213 , a pair of outer legs  214 , and a center leg  215 . The pair of the outer legs  214  is provided so as to be protruded above both ends of the end faces  213 , and the center leg  215  is provided between the pair of the outer legs  214  so as to be protruded above the end faces  213 . Here, the center leg  215  is formed into the asymmetrical shape so as to accord with the cross-section shape of the cavity of the hoisting drum  202 . 
     The coils  216  are wound on the hoisting drum  202 , and a tape is wound on a periphery thereof. The coils  216  include a first coil and second coil. As described above, each center leg  215  of the pair of cores  212  is inserted with respect to the hoisting drum  202  of the bobbin  1  in which the coils  216  are wound on the hoisting drum  202 , and the outer legs  214  are fitted into between the terminal block  207  for the first side terminal and the terminal block  208  for the second side terminal so as to incorporate the cores  212  with the bobbin  201 . The coil is fixed on the periphery of incorporated cores  212  by the tape (not shown) or an adhesive bonding. 
       FIG. 30  is a side view showing an operating state in which the bobbin  201  is set to a winding shaft  202  of a winding machine and the coil is wound on the bobbin, and  FIG. 31  is a cross-section view taken along a line F-F in  FIG. 30 . As shown in  FIGS. 30 and 31 , the cross-section of the coil shaft  221  is formed into the shape in accordance with the cavity of the hoisting drum  202  of the bobbin  201 . When the winding operation is conducted by using the winding machine  220 , the hoisting drum  202  of the bobbin  201  is fitted into the coil shaft  221  in which an initial setting position of a rotational direction is predetermined in advance, the winding is tied into the first side terminal  205  and the second side terminal  206 , and the coil shaft  221  is rotated. Accordingly, the winding is conducted on the hoisting drum  202 . Such winding process is conducted with the plural number requiring the number of the winding in the transformer. In a plurality of the winding processes, the initial setting position of the rotational direction of the winding machine  221  may differ from each other. 
     When the winding process is conducted as described above, since the periphery of the hoisting drum  202  is formed into the asymmetrical shape by the X-axis, it is easily discriminated by viewing from the position of the rotational direction of the bobbin  201 . For this reason, the bobbin  201  is easily set to the coil shaft  221 , and the operating efficiency is improved. 
     In addition, when the cavity and the coil shaft  221  of the hoisting drum  202  of the bobbin  201  according to the invention are formed into the asymmetrical shape by the X-axis, if the direction of the hoisting drum  202  of the bobbin  201  does not match up to the direction of the coil shaft  221 , it is impossible to set the bobbin  201 . Accordingly, when the bobbin  201  is set to the coil shaft  221 , the direction of the bobbin  201  is automatically determined, and it may avoid the error of the set. 
     In addition, since the initial setting position of the rotational direction of the coil shaft  221  is constant, the initial setting position of the rotational direction of the terminal blocks  207  and  208 , the first side terminal  205 , and the second side terminal  206 A are constant. Accordingly, it may avoid that the coil terminals do not match to the subject terminals. It may avoid that the operating failure above-described produces in the impression of the seal, measurement, and mounting on the substrate. As a result, the yield ratio is improved in a manufacturing of the transformer. 
     Referring to  FIG. 27 , the cavity of the hoisting drum  202  is configured such that the direction of the Y-axis is set as a broad-width, and the direction of the X-axis is set as a narrow-width. However, it may be configured such that the directional widths of the X-axis and the Y-axis are equal, or the directional width of the Y-axis is narrow, and the directional width of the X-axis is broad. In addition, the cavity or the periphery of the hoisting drum  202  may be configured such that two regions divided by the X-axis are formed the asymmetrical shape, and two regions divided by the Y-axis are also formed the asymmetrical shape 
       FIGS. 32 to 37  are a cross-section view showing another embodiment of the bobbin according to the invention, respectively. In  FIGS. 32 to 37 , the reference numbers as same as those of  FIG. 27  indicate the same parts. In  FIG. 32 , the cavity (like the periphery) of the hoisting drum  202 A is divided into one region  210 A and the other region  211 A by the X-axis, respectively. The one region  210 A is formed into a dome shape, and the other region  211 A is formed into the rectangular shape. Accordingly, two regions  210 A and  211 A are asymmetrical shape. 
     In  FIG. 33 , the cavity (like the periphery) of the hoisting drum  202 B is divided into one region  210 B and the other region  211 B by the X-axis, respectively. A tip of the one region  210 B is formed into an angular shape, and the other region  211 B is formed into the rectangular shape. Accordingly, two regions  210 B and  211 B are asymmetrical shape. 
     In  FIG. 34 , the cavity (like the periphery) of the hoisting drum  202 C is divided into one region  210 C and the other region  211 C by the X-axis, respectively. A tip of the one region  210 C and the other region  211 C are formed into an arc shape and curvature radii of the arc shape are different from each other. Accordingly, two regions  210 C and  211 C are asymmetrical shape. 
     In  FIG. 35 , the cavity (like the periphery) of the hoisting drum  202 D is divided into a one region  210 D and the other region  211 D by the X-axis, respectively. The cross-section thereof is formed into a triangle-like shape as a whole. Accordingly, two regions  210 D and  211 D divided by the X-axis are asymmetrical shape. 
     In  FIG. 36 , the cavity (like the periphery) of the hoisting drum  202 E is divided into one region  210 E and the other region  211 E by the X-axis, respectively. Two regions  210 E and  211 E are asymmetrical shape, and two regions divided by the Y-axis are also asymmetrical shape each other. Furthermore, in either case which is divided by the division lines of the directions or positions, the divided two regions are asymmetrical shape each other. 
     In  FIG. 37 , a longitudinal direction in the section of a hoisting drum  202 F having an oval-like shape is set as the Y-axis and the Y-axis is formed on the slant relative to the opposing direction of the terminal blocks  207  and  208 . 
     Effects according to each embodiment of  FIGS. 32 to 37  are the same as in the embodiments of  FIGS. 24 to 31 . 
       FIG. 38  is a rear view showing another embodiment of the bobbin according to the invention, and  FIG. 39  is a side view of the bobbin of  FIG. 38 . The bobbin  223  is to use in a horizontal transformer. The bobbin  223  is configured such that a first side terminal block  227  and a second side terminal block  228  are provided at protrusions  225  and  226  of both ends of the hoisting drum  224 . By this configuration, mounting faces  229  are formed on a substrate which is not shown. 
     In  FIG. 38 , O indicates the vertical-horizontal center point of the cavity of the hoisting drum  223 . In the cross-section vertical to the core direction of the cavity of the hoisting drum  224 , the Y-axis is the center line vertical to the mounting faces  229 . Further, the X-axis is the center line parallel to the mounting faces  229 . At this time, the cross-section of the cavity of the hoisting drum  224  is formed such that the section of one region  230  and the section of the other region  231  of the cavity of the hoisting drum  224  divided by the X-axis is formed into the asymmetrical shape. asymmetrical shape. 
     In embodiments of  FIGS. 38 and 39 , the transformer is configured such that the coil is wound on the hoisting drum  224 , the center leg of the E type core is inserted into the hoisting drum  224   a , and the outer legs are located at both sides of the coil. 
     In the embodiment related to the horizontal transformer of  FIGS. 38 and 39 , it may obtain the effects such as an improvement of the operating efficiency, a reduction of the operating failure, and an improvement of the yield ratio in each process such as the impression of the seal, measurement, and mounting on the substrate as well as in the embodiments shown in  FIGS. 24 to 37 . 
     In addition, two regions of the cavity of the hoisting drum  224  divided by the Y-axis may be also formed into the asymmetrical shape in this horizontal transformer. Also, in this case, it is possible to obtain the effects such as the improvement of the operating efficiency and the reduction of the operating failure. Furthermore, two regions of the cavity divided by the X-axis and the Y-axis, respectively, may be formed into the asymmetrical shape in the horizontal transformer. In addition, two regions of the periphery of the hoisting drum  224  divided by the X-axis and the Y-axis, respectively, may be formed into the asymmetrical shape. 
     Fourth Embodiment 
       FIGS. 40 to 42  are a plane view, a side view, and a bottom view showing a first embodiment of a ferrite core according to the present invention, respectively. In  FIG. 40 , the core  301  is an E type core having a center leg  304  which is formed in a center of one face of an end plate  302  so as to protrude and an outer leg  303  which is formed in both ends so as to protrude. O indicates a vertical-horizontal center point of the core  301 . 
     Here, a Y-axis is the center line of an opposing direction of terminal blocks  311  and  312  (see  FIGS. 43 to 45 ), as will be described below, in a cross-section of a direction vertical to the core of the center leg  304 , and a X-axis is the center line of the direction vertical to the opposing direction of the terminal blocks in the cross-section. At this time, in this embodiment, the cross-section is formed such that the cross-section of an upper region  304   a  and a lower region  304   b  divided by the X-axis as shown in  FIG. 40  are asymmetrical. In addition, left and light regions of the center leg  304  divided by the Y-axis are a symmetrical shape. That is, the number of a symmetrical division lines is one. In the embodiment, the cross-section of the center leg  304  has approximately an oval shape. Further, two regions  303   a  and  303   b  of the outer leg  303  divided by the X-axis are also asymmetrical. 
       FIGS. 43 to 45  is example of a transformer using the ferrite cores  301 , respectively. This embodiment shows a vertical type transformer in which the terminal blocks  311  and  312  mounting a first side terminal  313  and second side terminal  314  on only one side guard  308  of the guards  308  and  309  are provided. The guards  308  and  309  are formed in both ends of a hoisting drum  306  which winds a coil  310  on a bobbin  305 . 
     The coil  310  includes a first coil and second coil, and a periphery of the coil  310  is wound by a tape. Each center  304  of a pair of cores  1  is inserted with respect to the hoisting drum of the bobbin  305  on which the coil  310  is wound, and the outer legs  303  are fitted into between the terminal block  311  for the first side terminal and the terminal block  312  for the second side terminal so as to incorporate the cores  301  with the bobbin  305 . Accordingly, a core joint portion of the hoisting drum  306  or the guards  308  and  309  has the asymmetrical shape in which the center leg  304  or the outer leg  303  is combined with the asymmetrical shape. The coil is fixed on the periphery of incorporated cores  1  above-described by the tape (not shown) or an adhesive bonding. 
     As shown in  FIG. 40 , in this embodiment, a distance G 2  between the upper outer legs  303  is longer than a distance G 1  between the lower outer legs  303 . That is, even though it is set such that the distance between the ends of the outer legs  303  opposite to a broad-width side of the center leg is longer than the distance of others side, the center leg  304  and the outer leg  303  may be set at regular distances regarding all lateral faces of the center leg. Accordingly, even though the transformer is configured as described above, the transformer can prevent a magnetic saturation due to partially concentrate of the magnetic flux, can prevent a characteristic from being deteriorated, and can be miniaturized. 
     In addition, since the distance G 2  between the ends of at least one side of the outer legs  303  are extended, it may be subjected to increase the number of coil terminals extracted from a portion between the extended outer legs. Furthermore, since it is possible to thicken a wire diameter, to use a twisted wire, and to increase the number of the coil terminals, a copper loss is reduced. As a result, it is possible to provide the transformer having a good efficiency and being capable of outputting a large current. In addition, since the increased coil terminals or the thicken wires or the twisted wires are extracted from the portion between the extended outer legs  303 , a tube or the tape for insulating a gap between the coil terminal and the outer leg  303  is not necessary, and it can contribute to improve an operating efficiency. 
     In addition, in the vertical type transformer according to this embodiment, by allowing the terminal block  312  for a second coil to correspond to the end which the distance G 2  between the outer legs  303  is long, it may be ensured to widen an extraction region of a few the second coil terminal. Accordingly, as described above, the transformer can prevent a magnetic saturation, a characteristic from being deteriorated, and can be miniaturized. In addition, it is possible to obtain the transformer in which an output capacitance increases by using the thick wires or the twisted wires to the second coil and which easily corresponds to a new device demand by increasing the number of the second coil. As a result, it is easy to extract the coil terminal. 
     As shown in  FIG. 42 , according to the embodiment, a hole-shaped concave portion  317  is formed in an end face  302   a  opposite to a protruded face of the center leg  304  or the outer leg  303  in the end plate  302  of the core  301 . The concave portion  317  is a direction recognizable portion for distinguishing whether a divided region  304   b  having a large area (or a divided region  304   a  having a small area) is existed or not in one end of the center leg  304  and the outer leg  303 , that is, the both ends divided by the X-axis serving as the division line. In this embodiment, the concave portion  317  is provided on the Y-axis and the upper side (the divided region  304   b  side of the center leg  304  having the large area) which is higher than the center point O so as to be displaced to the upper position. In addition, according to this embodiment, the concave portion  317  has a circular shape, but may have another shape such as a square. 
       FIG. 45  shows a region  318  having a low magnetic flux density and a region  319  having a high magnetic flux density producing by the coil  310  in the core section. Here, two ferrite cores  301  are incorporated to each other as the transformer. In  FIG. 45 , the concave portion  317  is provided on the end having the large area in the center of the end face  302   a . That is, the concave portion  317  is formed in the position and depth which the region  319  having the high magnetic flux density does not exist. 
     As shown in  FIGS. 47A ,  47 B, and  47 C, the cross-section of the concave portion  317  may be formed into any one of a rectangular shape, the circular shape, a triangular shape and so on. The concave portion  317  may be provided by a cutting at the same time or after a molding of the core  301 . 
     In an assembly of the transformer using the core  301 , when a hoisting drum  306  of the bobbin  305  is arrayed vertically, and the core  301  is mounted from above by facing up the end plate  302  thereof, the sectional directions of the center leg  304  and the outer leg  303  of the core are is manifestly apparent viewed from the concave portion  317 . Accordingly, it is not required to confirm the sectional direction by allowing the core to reverse in such a manner in which a tip of the center leg  304  and outer leg  303  of the core is directed upwardly, when the core  301  is mounted on the bobbin  305 . As a result, the operating efficiency is improved. 
     In addition, when a product name or lot name is printed on the lateral portion  303   c  of the core  301  or the end plate  302   a , since the direction is easily confirmed while viewing from the concave portion  317 , it is not required to confirm the direction by allowing the core  301  to reverse, and the operating efficiency is improved. Furthermore, when an impression of a seal is conducted by an automatic printing, it is necessary that the sectional direction of the center leg  304  or the outer leg  303  of the core is uniformly arranged. However, even in this case, the sectional direction of the center leg  304  or outer leg  303  may be confirmed easily, and the operating efficiency is improved. Accordingly, it is possible to prevent a defection of the impression of the seal due to a difference of the direction. 
     In addition, according to this embodiment, the center leg  304  has the asymmetrical shape in which the one region  304   b  and the other region  304   a  divided by the X-axis is broad and narrow, respectively. Also, the regions divided by the Y-axis may be asymmetrical. 
       FIGS. 48 to 52  is bottom view showing another embodiment of the core according to the present invention, respectively. In these figures, the reference numbers as same as those of  FIG. 43  indicate the same parts. In  FIG. 48 , a groove-like concave portion  317 A is formed at the Y-axis direction in the center of the end face  302   a . The concave portion  317 A is provided so as to be displaced to the Y-axis direction (the upper side or lower side in  FIG. 48 ) other than the center point O in the end face. Accordingly, it is possible to distinguish the direction of the center leg  304  or the outer leg  303  by only viewing from the end face. The cross-section of the concave portion  317 A may be formed into various shapes shown in  FIGS. 47A ,  47 B, and  47 C. 
     In  FIG. 49 , the direction recognizable portion  323  consisting of a C face (a slanted face  320 ) shown in  FIG. 52A , a R face ( 321 ) shown in  FIG. 52B , or a stepped portion ( 322 ) shown in  FIG. 52C  is formed on the corner between the end plate  302  and the one outer leg  303   a.    
     According to this embodiment, since a position of a broad width portion  304   b  or narrow width portion  304   a  is recognized whether exists either in the upper or lower of  FIG. 49  depending on the position of the direction recognizable portion  323  which exists in a left or light of  FIG. 49 , the sectional direction of the center leg  304  or the outer leg  303  may be distinguished without allowing the core  301  to reverse. 
     In  FIG. 50 , the direction recognizable portion  324  consisting of the C face, R face, or stepped portion shown in  FIGS. 52A to 52C  is formed on the outer corner of the one outer leg  303 . In addition, in  FIG. 51 , the direction recognizable portions  324  are formed on the same side of the outer corners of both outer legs  303 . The sectional direction of the center leg  304  or the outer leg  303  may be distinguished, without reversing the core  301 , by the direction recognizable portions  323  and  324  formed on the corner as described above. 
       FIG. 53  is another embodiment according to the invention. In  FIG. 53 , the groove-like concave portion  317 B is formed on the lateral side serving as an outer face of the one outer leg  303 . That is, the groove-like concave portion  317 B is formed above or below the X-axis as shown in  FIG. 53 . As shown in  FIG. 53 , the concave portion  317 B may be formed on one side or both sides. According to the embodiment of  FIG. 314 , the sectional direction of the center leg  304  or the outer leg  303  may be distinguished without allowing the core  301  to reverse. In the embodiment, it is preferable that the concave portion is formed on the outer side of the broad width side  303   a  of the outer leg  303  having the low magnetic flux density in that there has little influence on characteristics of the transformer. 
     Even in any one of the embodiments as described above, since the concave portions  317 ,  317 A, and  317 B or the direction recognizable portions  323  and  324  are provided on places in which the magnetic flux density is low or there is no magnetic flux, it has no influence on the characteristics of the transformer. In addition, these concave portions  317 ,  317 A, and  317 B or the direction recognizable portions  323  and  324  may be formed into the same or different shapes. 
       FIG. 54  is a front view showing another embodiment of the transformer applying the core according to the invention, and  FIG. 55  is a side view of the transformer of  FIG. 54 . In this horizontal transformer, a bobbin  330  is configured such that a first side terminal block  335  and a second side terminal block  336  are provided on guards  333  and  334  of both ends of the hoisting drum  331  which winds a coil  332 . By this configuration, a mounting face  337  is formed on a substrate which is not shown. 
     The core  301  shown in  FIGS. 40 to 42  is also used in horizontal transformer. O indicates the vertical-horizontal center point of the core  301 , and also the center point of the center leg  304  of the core  301 . As described above, in the cross-section vertical to the center leg  304  of the core  301 , the Y-axis is the center line vertical to the mounting face  337 . Further, the X-axis is the center line parallel to the mounting face  337 . At this time, the cross-section of the center leg  304  is formed such that two regions divided by the X-axis is formed into the asymmetrical shape. The two regions of the cross-section of the outer leg  303  divided by the X-axis are also symmetrical. Even in the horizontal transformer, the concave portions  317 ,  317 A, and  317 B serving as the direction recognizable portion or the direction recognizable portions  323  and  324  are provided, accordingly, it is possible to prevent the defection of the impression of the seal and to improve the operating efficiency in the assembly operation. 
     In addition, two regions of the center leg divided by the Y-axis may be also formed into the asymmetrical shape in this horizontal transformer. Also, in this case, it is possible to prevent the defection of the impression of the seal and to improve the operating efficiency.