Patent Publication Number: US-2009231078-A1

Title: Switching Transformer

Description:
TECHNICAL FIELD 
     The present invention relates to a small switching transformer. 
     BACKGROUND ART 
     Conventionally, this type of switching transformer generally uses a coil bobbin in which there is formed, at an end of a hollow and cylindrical winding drum part, a terminal block having terminals. And, the switching transformer is configured with coils wound around the outer circumference of the winding drum part of this coil bobbin, and with a core having a center leg inserted in the winding drum part. 
     In the above-described conventional switching transformer with a configuration in which electric wires are wound around the outer circumference of the hollow winding drum part of a coil bobbin, as described above, there is a slight gap between the outer circumference of the center leg of the core inserted into the winding drum part and the inner circumferential surface of the winding drum part. Further, due to the thickness of the winding drum part of approximately 1 mm, the coils are distanced from the center leg of the core, and the coupling factor is diminished, which is not preferable in view of the performance. 
     Furthermore, the circumferential length of the winding drum part around which the coils are wound is increased in proportion to the sum of the thickness of the winding drum part of the coil bobbin and the gap between the center-leg of the core and the winding drum part of the coil bobbin. Therefore, the consumption of the electric wires, insulating tapes and so on to be wound around the outer circumference of the winding drum pan increases, in proportion to which the cost gets higher, leading to a considerably high cost in the mass production of the products. 
     Today, when the price competition is severe, the costs have to be reduced, while performance be improved, as well as size reductions be accomplished, in order for a company to get ahead of other competing companies. 
     For improving the coupling factor by shortening the distance between the center leg and the coils, for reducing the costs by reducing the consumption of the electric wires and the insulating tapes, and for accomplishing size reductions, it is conceivable to wind the electric wires directly on the outer circumference of the center-leg core. 
     As such a configuration, there is a coil part as shown in  FIG. 10  (Japanese Patent Laid-Open No. 10-92655), 
     In this coil part, an insulating plate  100  having a plurality of electrode parts is bent and mounted to a coil-placing bottom portion  102  of a core  101 , a coil  103  is provided on the insulating plate  100  that covers the coil-placing bottom portion, and leads of the coil  103  are connected to electrode parts  104 , thereby a winding drum part of a coil bobbin between a center-leg core and a coil is made unnecessary. 
     Patent Document: 1 Japanese Patent Application, Laid-Open No. 10-92655 
     However, the above-described conventional example had a problem that, in attaching the insulating plate  100 , it is necessary to bend and mount the insulating plate  100  to the coil-placing bottom portion  102 , and hence it requires the bending process as well as the work of attaching the electrodes  104  as terminals respectively at four places of the insulating plate  100 , so, the assembling is very complicated. 
     Furthermore, because side-leg cores  101   b  are provided in a standing manner respectively on the outer side of a center-leg core  101   a  of the core  101  on which the coil  103  is to be provided, these side-leg cores  101   b  constitute an obstacle that prevents winding the coil  103  directly on the outer circumference of the center-leg core  101   a  while rotating the center-leg core  101   a  using a winding machine. In this respect, also, the conventional example had a problem that the workability is very low. 
     The present invention has been proposed in view of the above-described circumstances, and the object of the invention is to provide a switching transformer, which is suitable for mass production, and in which the material costs are cut down while the performance is improved, the cost and size are reduced and the assemblability is improved. 
     DISCLOSURE OF THE INVENTION 
     The method of manufacturing a switching transformer of the present invention is characterized in comprising the steps of; inserting a center-leg core of a center-leg-having core which has a substantially inverted T-shaped section, into a hole for inserting the center-leg core formed in a center part of a terminal block which has a substantially flat upper surface and terminals implanted in a lower surface thereof, to integrate the terminal block and the center-leg-having core; rotating the center-leg core to wind an electric wire around an outer circumference of the center-leg core protruding from the upper surface of the terminal block, to mount a coil; and subsequently, assembling the switching transformer by placing, from the upper surface side of the terminal block, a substantially Π-shaped, side-leg-having C-type core having side leg cores formed on both end portions of a connecting part, making an inner surface of the connecting part abut to a top end surface of the center leg core, and connecting bottom faces of the side leg cores with both end portions of a top surface of a core body of the center-leg-having core via a gap. 
     The above-described method of manufacturing a switching transformer further comprises, winding insulating paper on the outer circumference of the center-leg core, winding margin tapes respectively on both end portions of the center-leg core, and winding the coil between the margin tapes. 
     Furthermore, the above-described method of manufacturing a switching transformer comprises fixing the terminal block having the center-leg-having core to a rotatable first jig, making the top end of the center-leg core be supported by a second jig, and rotating the terminal block through the first jig, to wind the electric wire around the outer circumference of the center-leg core. 
     The switching transformer is characterized in comprising; a terminal block whose upper surface is formed substantially flat, in a side portion of a lower surface of which there are implanted terminals, and in a center portion of which there is formed a hole; a substantially-inverted-T-shaped center-leg-having core, whose core body is positioned on a lower face of the terminal block, and in which a center-leg core is formed on a center part of the core body, and the center-leg core is inserted through the hole and protruding from the upper surface of the terminal block; a coil wound around an outer circumference of the center-leg core; and a substantially Π-shaped, side-leg-having C-type core, which is incorporated from the upper surface side of the terminal block so as to straddle the coil, and in which bottom surfaces of side leg cores formed on both end portions of a connecting part are connected to both end portions of a top surface of the core body of the center-leg-having core via a gap, and an inner surface of the connecting part is abutted to a top end surface of the center-leg core. 
     In the above-described switching transformer, a rib is formed around the hole of the terminal block through which the center-leg core is to be inserted. 
     In the above-described switching transformer, insulating paper is wound around the outer circumference of the center-leg core which is inserted into the hole of the terminal block, a margin tape is wound on each of both end portions of the center-leg core protruding from the upper surface of the terminal block, and the coil is wound between the margin tapes. 
     In the above-described switching transformer, a substantially rectangular notch is formed in each end face of the terminal block, each of end portions of the core body of the center-leg-having core is positioned on each of the notches, and a bottom face of each of the side-leg cores is connected to each of the end portions via a gap. 
     According to the present invention, since the coils are wound around the outer circumference of the center-leg core protruding from the upper surface of the terminal block  1 , the assembling workability is improved and the distance from the center part of the center-leg core to the coil is made shorter, leading to an increase in the coupling factor, as a result of which, there are effects that the efficiency is improved and power is obtained. In addition to this advantage of an increase in productivity and performance, the nonuse of a coil bobbin with a winding drum part ensures a small size, and the consumption of electric wires, insulating tapes and so on decreases. In addition, because the terminal block does not have a winding drum part, the amount of the material for the terminal block is reduced, enabling the costs to be reduced. 
     Because the center-leg core is supported with the rib, it is possible to stably support the center-leg core. 
     Furthermore, because the side-leg cores of the C-type core are disposed in the notches of the terminal block to ensure that these side-leg cores do not project outside of the terminal block, size reduction is made possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of an embodiment of the present invention; 
         FIG. 2  is an explanatory diagram showing how a terminal block used in an embodiment of the present invention is incorporated into a center-leg-having core; 
         FIG. 3  is a perspective view of an assemble in which a terminal block and a center-leg-having core used in an embodiment of the present invention, are integrated; 
         FIG. 4  is a perspective view of a state in which a coil has been wound on the above-described assembly; 
         FIG. 5(   a ) is a diagram showing how an assembly is attached to a jig, and  FIG. 5(   b ) is a diagram showing how an electric wire is wound on a center-leg core of a terminal block to which a jig is attached, to wind a coil; 
         FIG. 6  is an explanatory diagram showing how a C-type core is integrated with a terminal block on which a coil is wound; 
         FIG. 7  is a perspective view of an assembled switching transformer of the present invention; 
         FIG. 8  shows a section taken along line A-A in  FIG. 7 ; 
         FIG. 9  shows the relationship between the coupling factor and the change of the gap of the core; and 
         FIG. 10  is an exploded perspective view of a conventional example. 
     
    
    
     DESCRIPTION OF REFERENTIAL NUMERALS 
       1  Terminal block 
       1   a  Upper surface 
       1   b  Leading groove 
       1   c  Notch 
       1   d  Hole 
       1   e  Rib 
       1   f  Partition wall 
       1   g  Core body housing portion 
       2  Terminal 
       3  Center-leg-having core 
       3   a  Core body 
       3   b  Center-leg core 
       4  C-ape core 
       4   a  Connecting part 
       4   b  Side-leg core 
       5  Margin tape 
       6  Coil 
       6   a  Electric wire 
       7  First jig 
       8  Second jig 
       9  Insulating tape 
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Embodiments according to the present invention will be described below with references to the drawings. 
     Embodiment 1 
       FIG. 1  is an exploded perspective view of Embodiment 1 of the present invention. 
     Without an use of a conventional coil bobbin with a winding drum part, the switching transformer of the present invention is configured with, as its main components, a terminal block  1  which has terminals  2  at both end portions of the lower surface in the illustrated condition and whose upper surface  1   a  is almost flat, a center-leg-having core  3  which is incorporated from the lower side in the illustrated condition and has a substantially T-shaped vertical cross section, and a substantially inverted U-shaped, side-leg-having, C-type core  4  that is incorporated from the upper side and whose side legs are placed on respective end portions of the top surface of the core. 
     The center-leg-having core  3 , which is made of ferrite, is composed or an I-shaped core body  3   a  and a cylindrical center leg  3   b  provided in a standing manner on the center part of the top surface of this core body  3   a.    
     The C-type core  4  is also made of ferrite, and side-leg cores  4   b  are provided respectively at both ends of an I-shaped connecting part  4   a.    
     The terminal block  1  is formed substantially rectangular as viewed from the upper side. In both side portions, there are formed at appropriate intervals a plurality of leading grooves  1   b  for guiding the lead wires (not shown) of the coil, and a plurality of terminals  2  are implanted in a lower surface. 
     In each of both ends of the terminal block  1 , there is formed a substantially rectangular notch  1   c  for disposing each side-leg core  4   b  adjacently on the top surface of each end portion of the core body  3   a  of the center-leg-having core  3 . The shape of this notch  1   c  corresponds to the shape of the side-leg core  4   b.    
     Furthermore, in the middle part of the terminal block  1 , there is formed a round hole  1   d  through which the center-leg core  3   b  is to be inserted to protrude to the side of the upper surface  1   a , and around the hole  1   d  is formed a ring-shaped rib  1   e  for stably supporting the inserted center-leg core  3   b.  This rib  1   e  is formed on the upper surface  1   a  of the terminal block  1 . 
     On the lower surface of the terminal block  1 , there are formed rib-like partition walls  1   f , which are spaced from and facing each other, and a core body housing portion  1   g  that houses the core body  3   a  of the center-leg core  3  is formed by the pair of partition walls  1   f . The partition walls  1   f  are formed on the inner side of the terminals  2 . 
     Next, the assembling method will be described. 
     First, the terminal block  1  is moved downward to the center-leg-having core  3  side as indicated by the arrows in  FIGS. 1 and 2 , the center-leg core  3   b  is inserted into the hole  1   d  of the terminal block  1  as shown in  FIG. 3 , the core body  3   a  is disposed in the core body housing portion  1   g , and the center-leg-having core  3  is incorporated into the terminal block  1 , whereby both are integrated. Alternatively, the center-leg-having core  3  may be moved upward to be incorporated into the terminal block  1 . 
     Next, as shown in  FIG. 4 , margin tapes  5  are wound around the upper and lower portions of the center-leg core and a coil  6  is wound between the margin tapes  5 . 
     As shown in  FIG. 5(   a ), in winding the coil  6 , the terminal block  1  with the center-leg-having core  3  incorporated therein is set on a first jig  7  which is capable of rotation and connected to a motor (not shown), and a second jig  8  is set on a top end of the center-leg core  3   b,  to support the center-leg core  3   b.    
     In the setting of the first jig  7 , the partition walls  1   f  of the terminal block  1  sandwich and support the top surface  7   a  and the bottom surface  7   b  of the main body of the first jig  7 , the front surface  7   c  of the main body of the first jig is abutted and held to the bottom surface of the core body  3   a  of the T-shaped, center-leg-having core  3 . Because the core is a T-shaped core being incorporated into the terminal block  1 , not being an I-shaped core consisting only of a center-leg core, it can be firmly fixed to the first jig  7  by the core body  3   a  part. And as shown in  FIG. 5(   b ), by rotating the first jig  7  as indicated by the arrow, an electric wire  6   a  is wound around the outer circumference of the center-leg core  3   b,  thereby the coil  6  can be mounted. 
     In the present invention, because no side-leg core is present on either side of the center-leg-having core  3 , it is possible to wind the coil  6  directly on the outer circumference of the center-leg core  3   b  easily and speedily as described above, so, the assemblability is improved, and the coupling factor can be improved, because no winding drum part of a coil bobbin is interposed between the coil  6  and the center-leg core  3   b.    
     Furthermore, because the circumferential length is shortened by the elimination of the winding drum part, the consumption of the electric wire  6   a  is reduced, which leads to a cost reduction. 
     In here, as is generally known, an insulating tape (not shown) is wound on the outer circumference of the center-leg core  3   b,  before the winding of the electric wire  6   a . Also, margin tapes  5  are wound on the upper and lower portions of the center-leg core  3   b  protruding from the top surface  1   a  of the terminal block  1 . However, in  FIG. 5(   b ) showing how the coil is wound, the illustration of the margin tapes  5 , the insulating paper and the like is omitted. Also the insulating tape and the margin tapes  5  can be wound around the center-leg core  3   b  by using the first jig  7 . 
     After the mounting of the coil  6  on the terminal block  1 , the C-type core  4  having the side-leg cores  4   b  is integrated, with the bottom faces of the side-leg cores  4   b  being arranged to face the respective end portions of the top surface of the core body  3   a  of the center-leg-having core  3 , located on the notches  1   c  of the terminal block  1 , and with the top end face of the center-leg core  3   b  being made abutting to the inner surface of the connecting part  4   a  of the C-type core  4 , thereby a switching transformer is assembled, as shown in  FIGS. 6 and 7 . 
     In here, though not particularly illustrated, magnetic gaps can be easily provided by providing insulating paper or a spacer made of resin between the bottom faces of the side-leg cores  4   b  of the C-type core  4  and the top surface of the core body  3   a  of the center-leg-having core  3  facing these bottom faces, and the side-leg cores  4   b  and the core body  3   a  can be connected through these gaps. 
     In order to prevent the coming apart of this assembly, for example, a tape (not shown) may be wounded on the outer circumference of the core composed of the center-leg-having core  3  and the C-type core  4 , or the outer portion of an abutting faces may be bonded. 
       FIG. 8  shows a section taken along line A-A in  FIG. 7 . In this embodiment, the coil  6  is composed of an inner winding  6 A, a middle winding  6 B and an outer winding  6 C. In its assembling, an insulating tape  9  is first wound on the outer circumference, a margin tape  5  is wound on the outer circumference of the bottom end portion of the center-leg core  3   b  protruding from the rib  1   e  of the terminal block  1 , and a margin tape  5  is wound also on the upper end portion of the center-leg core  3   b.  And the inner winding  6 A is wound between these upper and lower margin tapes  5 , and an insulating tape  9  is wound on the outer circumference of the inner winding. Next, a margin tape  5  is wound on each of both end portions of the insulating tape, the middle winding  6 B is wound between the margin tapes, and an insulating tape  9  is wound on the outer circumference of the middle winding. Next a margin tape  5  is wound on each of both end portions, the outer winding  6 C is wound between the margin tapes, and an insulating tape  9  is wound on the outer circumference of the winding after the completion of the winding. 
       FIG. 9  shows the relationship between the coupling factor and the core gap obtained when the gap between the top surface of the core body  3   a  of the center-leg-having core  3  and the bottom faces of the side-leg cores  4   b  of the C-type core  4  changes, with a spacer (not shorten) interposed. In the present invention, in addition to the improvement of the coupling factor owing to the distance between the center-leg core  3   b  and the coil  6  shortened in proportion to the not interposed winding drum part, the coupling factor can be further improved by distributing the gaps. In the figure, CTR type represents a switching transformer of the present invention and EER type represents a switching transformer in which a gap is provided at the top end of a center-leg core. The switching transformer of the present invention has the advantage that the coupling factor is further improved. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be applied to a small switching transformer used in a power supply device of consumer electronic equipment.