Patent Publication Number: US-2009230869-A1

Title: Transformer

Description:
TECHNICAL FIELD 
     The present invention relates to a transformer used for an inverter for a backlight device of a liquid crystal display apparatus, and more particularly, to a transformer to which a lamp as a light source of a backlight device is directly attached. 
     BACKGROUND ART 
     Since a liquid crystal display used as a display device, e.g., a liquid crystal monitor and a liquid crystal TV apparatus does not use light emission, it requires an illuminating device such as a backlight device. As a structure of the backlight device, an edge lighting system and a direct lighting system are well known. In the edge lighting system, a cold cathode lamp as a light source is arranged to the side surface of a light guide plate, light is incident on the light guide plate, and a diffuser is illuminated. In the direct lighting system, a discharge lamp, e.g., a cold cathode lamp as a light source just below a diffuser is arranged and illumination is performed. 
     A large-scaled liquid crystal display used as a display apparatus such as a liquid crystal TV apparatus needs high luminance, and mainly uses a direct-lighting backlight device having a plurality of lamps. In the direct-lighting backlight device having a plurality of lamps, output signals from a transformer for generating a high AC voltage by an inverter are applied to the lamps via a connector and a lamp cable, thereby lighting the lamps (refer to, e.g., Patent Document 1). 
       FIG. 11  is a plan view showing a backlight device  100  of a liquid crystal display apparatus disclosed in Patent Document 1. Referring to  FIG. 11 , the backlight device  100  comprises: a plurality of straight-tube lamps  110 ; and inverter substrates  112  arranged to both sides of the lamps  110 . Lamp driving circuit portions  112   a  are arranged to the left and right inverter substrates  112 . One half of the lamps  110  is driven by the lamp driving circuit portions  112   a  arranged to one side, and the other half of the lamps  110  is driven by the lamp driving circuit portions  112   a  arranged to the other side. In this case, high voltages generated by the lamp driving circuit portions  112   a  are applied to electrodes of the lamps  110  via high-voltage output connectors  115  and lamp cables  110   a , thereby lighting the lamps  110 . 
     In general, a cold cathode lamp is used as a lamp for the backlight device  100  shown in  FIG. 11 . The lighting operation of the cold cathode lamp requires a high AC voltage, and an output from an oscillation circuit is normally increased by a transformer, thereby lighting the cold cathode lamp. Since a high voltage is generated on the secondary side of the transformer, a winding structure is frequently used that windings on the secondary side are divided into a plurality of sections, flanges are arranged between the sections so as to prevent the occurrence of a breakdown due to the difference of a high potential between adjacent windings, and the creepage distance necessary for preventing a creeping discharge is thus kept. This high-voltage transformer is, e.g., a transformer shown in  FIG. 12  (refer to, e.g., Patent Document 2). 
       FIG. 12  is an exploded perspective view of a transformer  200  having the above-mentioned winding structure.  FIG. 13  is a plan view showing a coil bobbin  201  of the transformer  200  shown in  FIG. 12 . The transformer  200  comprises: the coil bobbin  201 ; a primary winding  207  and a secondary winding  208  wound around the coil bobbin  201 ; an I core  206  inserted into the coil bobbin  201 ; and an external core  205 . Terminal bases  203   a  and  203   b  in which terminal pins  204  are implanted are integrally formed at both ends of a hollow winding core  202  of the coil bobbin  201 , and the winding core  202  is divided a plurality of sections in the axial direction by a plurality of flanges  209   a  to  209   i  formed to the outer circumference of the winding core  202 . The primary winding  207  is wound around the section formed between the flange  209   b  for separating the primary winding  207  and the secondary winding  208  and the flange  209   a  on the side of the terminal base  203   a , and leads at both ends of the primary winding  207  are connected to the terminal pin  204  arranged to the terminal base  203   a . Further, the flanges  209   c  to  209   i  divide the interval between the flange  209   b  and the flange  209   i  on the side of the terminal base  203   b , the secondary winding  208  is divided and wound around a plurality of sections, and leads at both ends of the secondary winding  208  are connected to the terminal pin  204  arranged to the terminal base  203   b.    
     Moreover,  FIG. 14  is an exploded perspective view showing a transformer  300  with another structure (refer to, e.g., Patent Document 3). The transformer  300  comprises: a bobbin  301 ; a primary winding  307  and secondary windings  308  and  309  wound around the bobbin  301 ; an I core  322  inserted into the bobbin  301 ; a frame core  325 ; and an insulating holder  321 . A plurality of partitioning flanges  305  are formed to the outer circumference of a winding core of the bobbin  301 , and windings are wound around sections partitioned by the partitioning flanges  305 . Terminal bases  310  and  311  are formed at both ends of the winding core, and a plurality of terminal pins  312  are implanted in the terminal bases  310  and  311 . In the transformer  300 , the secondary windings  308  and  309  are wound around both sides of the primary winding  307 . 
     Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-349040 
     Patent Document 2: Japanese Unexamined Patent Application Publication No. 2000-003818 
     Patent Document 3: Japanese Registered Utility Model No. 
     DISCLOSURE OF INVENTION 
     Problem to be Solved by the Invention 
     Herein, there is the following problem in the case of applying the transformers  200  and  300  shown in  FIG. 12  to  FIG. 14  to the backlight device  100  shown in  FIG. 11 . That is, since the outputs from the secondary windings of the transformer need to be applied to the lamps  110  via the output connectors  115  in the backlight device  100  so as to light the lamps  110 , assembly operation of the lamp cables  110   a  for connecting the lamps  110  to the output connectors  115  is necessary. In particular, in the case of using a plurality of the lamps  110  in the backlight device  100 , the number of the output connectors  115  and the number of lamp cables  11   a  corresponding to the number of lamps  110  are required. As a consequence, the assembly operation step requires large labor and costs. Further, a high withstand-voltage is required for the output connectors  115  and the lamp cables  110   a . Therefore, a ratio of costs of parts as the output connectors  115  and the lamp cables  100   a  to the entire backlight device is high and the backlight device  100  needs the number of the output connectors  115  and the number of lamp cables  110   a , corresponding to the number of lamps. Hence, costs are not reduced. 
     The present invention is devised in consideration of the problems and it is an object of the present invention to provide a transformer in which costs of a backlight device are reduced by lighting lamps without using an additional member for connecting the lamps to the inverter. 
     Means for Solving the Problem 
     In order to accomplish the object, a transformer according to the present invention comprises: a terminal base in which a terminal pin is implanted; a bobbin formed by winding a primary winding and a secondary winding around the outer circumference of a winding core; and a core. A lamp connecting terminal is provided on the terminal base, and an electrode of a lamp is connected to the lamp connecting terminal, thereby attaching the lamp to the lamp connecting terminal. According to one aspect of the present invention, the terminal bases are individually arranged to both ends of the winding core, each of the terminal bases comprises two portions facing each other via a space, the lamp connecting terminal is provided on a surface of one side of the terminal base facing the other side thereof, the electrode of the lamp is connected to the lamp connecting terminal, and the lamp is attached and held onto the terminal base. 
     According to the present invention, the electrode of the lamp is directly connected to the lamp connecting terminal formed to the bobbin, thereby lighting the lamp without using a high-voltage output connector and a lamp cable. Thus, the output connector and the lamp cable resulting in high costs in the backlight device are omitted, thereby greatly reducing costs of the backlight device. Further, since the electrode of the lamp is directly connected to the lamp connecting terminal formed to the bobbin, it is possible to prevent the disconnection at the output connector and the lamp cable and the occurrence of corona discharge or arc discharge due to pseudo contact, thereby improving the reliability of the backlight device. 
     Furthermore, according to another aspect of the present invention, the lamp connecting terminal has elasticity. Preferably, elasticity is caused by a bending portion formed on the lamp connecting terminal. Since the lamp connecting terminal formed to the bobbin has the elasticity, the elastic deformation of the lamp connecting terminal suppresses the influence of the expansion and contraction of a reflecting plate, a substrate, or a frame, to which the transformer is attached, thereby preventing the damage of the lamp. 
     In addition, according to another aspect of the present invention, the transformer further comprises attaching means that attaches and holds the lamp at the terminal base. In this case, the attaching means is an elastic ring attached to the outer circumference of the lamp. The lamp may be held and attached to the terminal base by fitting the elastic ring into a groove arranged in the terminal base. Moreover, the attaching means may be an adhesive sheet and the lamp may be held and attached to the terminal base by the adhesive sheet. Alternatively, the attaching means may be used as a nail provided on the terminal base and the lamp may be attached and held onto the terminal base by the nail. Alternatively, the attaching means may be flexible resin and the lamp may be attached and held onto the terminal base by the flexible resin. The above-mentioned attaching means can attach and hold the lamp to the bobbin with a simple structure. 
     Further, according to another aspect of the present invention, the transformer is a leakage flux transformer, thereby omitting a ballast on the secondary side of the transformer. Hence, the number of parts can be reduced. 
     Furthermore, according to another aspect of the present invention, the secondary winding is divided to both sides of the primary winding and the divided windings are wound therearound. Outputs of the divided and wound portions of the secondary winding have inverse polarities with phases deviated by 180°. A preferable attaching structure of the lamp is specifically as follows. 
     That is, in the transformer according to the present invention, the lamp may be a bending tube and electrodes at both ends of the bending tube may be connected to the lamp connecting terminals. In addition, in the transformer according to the present invention, the lamp may comprise two straight tubes. In this case, electrodes on the low-voltage side of the two straight tubes may be connected, and electrodes on the high-voltage side of the two straight tubes may be connected to the lamp connecting terminals. With this structure, output voltages from the secondary winding on the high-voltage side of the lamps are applied with inverse polarities having phases deviated by 180°. Advantageously, a return line with a high withstand-voltage is not required. Alternatively, in the transformer according to the present invention, the electrodes on the high-voltage side of the two straight tubes may be connected to the lamp connecting terminal, and the electrodes on the low-voltage side of the two straight tubes may be connected to the GND. 
     Further, the transformer according to the present invention comprises two bobbins, and the lamp comprises two straight tubes. Then, one electrode of each of the two straight tubes is connected to the lamp connecting terminal of one of the bobbins, and the other electrode of each of the two straight tubes is connected to the lamp connecting terminal of the other bobbin. Both ends of the two straight tubes may be connected to the bobbins thereof. 
     Furthermore, according to another aspect of the present invention, the transformer according to the present invention comprises attaching means for attaching a reflecting plate of a backlight device or a printed circuit board. Preferably, the transformer may be integrated into an inverter for a backlight device of a liquid crystal display apparatus as a liquid crystal TV apparatus. 
     ADVANTAGES 
     With the above-mentioned structure according to the present invention, a lamp is lit without requiring an additional member for connecting the lamp to an inverter, such as a high-voltage output connector and lamp cable, and costs of the backlight device are greatly reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view showing a transformer in which a bending-tube-shaped lamp is connected according to the first embodiment of the present invention; 
         FIG. 2  is a plan view of a bobbin used in the transformer shown in  FIG. 1 ; 
         FIG. 3  is a front view showing the bobbin shown in  FIG. 2 ; 
         FIG. 4  is a bottom view showing the bobbin shown in  FIG. 2 ; 
         FIG. 5  is a side view showing the bobbin shown in  FIG. 2 ; 
         FIG. 6  is a diagram showing an example of a lamp connecting terminal; 
         FIG. 7  is a plan view showing one example of a transformer having a structure for connecting electrodes on the low-voltage sides of two straight-tube-shaped lamps according to the second embodiment of the present invention; 
         FIG. 8  is a plan view showing another example of the transformer having a structure for connecting the electrodes on the low-voltage sides of the two straight-tube-shaped lamps to the ground according to the second embodiment of the present invention; 
         FIG. 9  is a plan view showing a transformer having a structure for attaching bobbins to both ends of two straight-tube-shaped lamps according to the third embodiment of the present invention; 
         FIG. 10  is a diagram for explaining a state for attaching the transformer shown in  FIG. 9  to a reflecting plate of a backlight device; 
         FIG. 11  is a plan view showing a conventional backlight device of a liquid crystal display apparatus; 
         FIG. 12  is an exploded perspective view showing an example of a structure of the conventional transformer; 
         FIG. 13  is a plan view showing a bobbin of the transformer shown in  FIG. 13 ; and 
         FIG. 14  is an exploded perspective view showing another example of the structure of the conventional transformer. 
     
    
    
     REFERENCE NUMERALS 
     
         
         
           
               1  bobbin 
               2  winding core 
               3 ,  4  terminal base 
               3 C,  4 C space 
               10  primary winding 
               11  core 
               12 ,  13  secondary winding 
               14   a  to  14   d ,  16  terminal pin 
               17  lamp connecting terminal 
               17   a  bending portion 
               20 ,  30 ,  70  cold cathode lamp 
               20   a ,  30   a ,  30   b ,  70   a  electrode 
               21  elastic ring (attaching means) 
               24  reflecting plate 
               40 ,  50 ,  60 ,  80  transformer 
           
         
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinbelow, a description will be given of embodiments of the present invention with reference to the drawings. 
       FIG. 1  is a plan view showing a transformer  40  according to the first embodiment of the present invention.  FIG. 2  is a plan view showing a bobbin  1  of the transformer  40  shown in  FIG. 1 .  FIG. 3  is a front view showing the bobbin  1  shown in  FIG. 2 .  FIG. 4  is a bottom view showing the bobbin  1  shown in  FIG. 2 .  FIG. 5  is a left-side view showing the bobbin  1  shown in  FIG. 2 . 
     The transformer  40  according to the first embodiment comprises: the bobbin  1 ; a core  11 ; and a cold cathode lamp  20 . Both ends of the cold cathode lamp  20  as a U-shaped bending tube are attached and held to terminal portions  3 B and  4 B by attaching means  21 . Electrodes  20   a  at both ends of the cold cathode lamp  20  are connected to lamp connecting terminals  17  by soldering or laser welding. The core  11  comprises an I core  11 A and a squared core  11 B. The I core  11 A is inserted into a central hole  2   a  (refer to  FIG. 5 ) of a winding core  2 . The squared core  11 B forms an external frame of the bobbin  1 . As a material of the core  11 , a Ni—Zn-system ferrite indicating high electrical resistance is preferable. Further, preferably, the transformer  40  forms a leakage flux transformer by adjusting the gap of the core  11 . Accordingly, upon lighting the cold cathode lamp  20 , leakage inductance of the transformer  40  can function as a ballast. Incidentally, the cold cathode lamp  20  may be a C-shaped bending tube according to the first embodiment. 
     Referring to  FIGS. 2 to 5 , the bobbin  1  comprises terminal bases  3  and  4  at both ends of the hollow winding core  2  integrally with the winding core  2 . Flanges  5   a  and  5   b  are similarly formed to the external circumferential surface of the winding core  2  integrally with the winding core  2 . A primary winding  10  is wound between the flanges  5   a  and  5   b , and a lead of the primary winding  10  is wound around a terminal pin  14   b  implanted in the flange  5   a  and a terminal pin  14   c  implanted in the flange  5   b.    
     Further, a flange  6  is formed adjacently to a terminal base  3 , the interval between the flanges  5   a  and  6  are divided into a plurality of sections by a plurality of flanges  7   a  to  7   e . A secondary winding  12  is dividedly wound to the sections. One lead of the secondary winding  12  is wound around a terminal pin  14   a  implanted in the side surface of the flange  5   a , and the other lead thereof is wound around a terminal pin  16  implanted in a terminal base  3 A via a lead groove  15  formed to the terminal base  3 A. 
     Similarly, a flange  8  is formed adjacently to a terminal base  4 , and the interval between the flanges  5   b  and  8  is divided into a plurality of sections by a plurality of flanges  9   a  to  9   e , and a secondary winding  13  is dividedly wound to the sections. One lead of the secondary winding  13  is wound around a terminal pin  14   d  implanted in the side surface of the flange  5   b , and the other lead is wound around the terminal pin  16  implanted in the terminal base  4 A via the lead groove  15  formed to a terminal base  4 A. According to the first embodiment, output voltages of the secondary windings  12  and  13  are wound with inverse polarities having phases differing from each other by 180°. 
     The central portion of the terminal base  3  is divided, thereby forming the terminal bases  3 A and  3 B facing via a space  3 C. Similarly, the central portion of the terminal base  4  is also divided, thereby forming the terminal bases  4 A and  4 B facing via a space  4 C. Further, a lamp connecting terminal  17  positioned within the space  3 C is provided on the facing surface of the terminal bases  3 A and  3 B. Similarly, the lamp connecting terminal  17  positioned within the space  4 C is also provided on the facing surface of the terminal bases  4 A and  4 B. In addition, projected portions  3   a  and  3   b  formed to the terminal bases  3 A and  3 B function as stoppers of the core  11 . 
     Referring to  FIG. 6 , the lamp connecting terminal  17  is formed integrally with the terminal pin  16 , having a bending portion  17   a  with elasticity, and the terminal pin  16  is arranged at one end of the lamp connecting terminal  17  and a planar portion  17   b  is arranged at the other end thereof. Further, a hole  17   c  is formed to the planar portion  17   b , the electrode  20   a  of the cold cathode lamp  20  is inserted into the hole  17   c , and the electrode  20   a  of the cold cathode lamp  20  is connected to the planar portion  17   b  by, e.g., soldering or laser welding. 
     A caved portion  18  for accommodating the cold cathode lamp  20  is formed on the bottom surface sides of the terminal bases  3 B and  4 B, and the cold cathode lamp  20  is attached within the caved portion  18  by the attaching means  21 . According to the first embodiment, the attaching means  21  may be an elastic ring, e.g., O ring. In this case, the O ring attached to the outer circumference of the cold cathode lamp  20  is fit into a groove  18   a  formed to the inner circumference of the caved portion  18 , thereby attaching and holding the cold cathode lamp  20  to the caved portion  18 . 
     Further, as another attaching means, an adhesive sheet may be adhered to the inner circumference of the caved portion  18 , and the cold cathode lamp  20  may be attached and held to the caved portion  18  with the adhesive sheet. Alternatively, an engaging nail (or hook) may be formed to the inner circumference of the caved portion  18 , and the cold cathode lamp  20  may be attached and held to the caved portion  18  with the engaging nail. Further, alternatively, flexible resin, e.g., silicone resin may be adhered to the inner circumferential surface of the caved portion  18 , and the cold cathode lamp  20  may be attached and held to the caved portion  18  with the flexible resin. 
     Next, a description will be given of another embodiment with reference to  FIGS. 7 to 10 . In the following description, the same components as those in the transformer  40  are designated by the same reference numerals, and overlapped portions thereof will not be explained. In  FIGS. 7 to 10 , the core  11  is not shown for the purpose of a convenience. 
       FIGS. 7 and 8  are plan views showing transformers  50  and  60  using a cold cathode lamp  30  having two straight tubes according to the second embodiment of the present invention, in place of the cold cathode lamp  20  with the shape of the bending tube shown in  FIG. 1 . In the transformer  50  shown in  FIG. 7 , electrodes  30   b  on the low-voltage side of two cold cathode lamps  30  are connected, and electrodes  30   a  on the high-voltage side thereof are connected to the lamp connecting terminal  17  of the bobbin  1 . In the transformer  50 , output voltages from the secondary windings  12  and  13  of the bobbin  1  are applied to the electrodes  30   a  on the high-voltage side of the cold cathode lamps  30  with inverse polarities having phases differing from each other by 180°. Accordingly, a return line with a high withstand-voltage is not required. Further, in the cold cathode lamp  30  having the two straight tubes, the electrodes  30   a  on the high-voltage side may be connected to the lamp connecting terminal  17 , and the electrodes  30   b  on the low-voltage side may be connected to the GND, like the transformer  60  shown in  FIG. 8 . 
       FIG. 9  is a plan view showing another example of the structure of a transformer using a cold cathode lamp  70  with two straight tubes according to the third embodiment of the present invention. In a transformer  80  shown in  FIG. 9 , other bobbins  1  are connected to both ends of the cold cathode lamp  70 , and output voltages from the secondary windings  12  and  13  of the bobbins  1  at both ends of, the cold cathode lamp  70  are applied to electrodes  70   a  at both ends thereof. 
       FIG. 10  is a diagram for explaining the structure in the case of applying the transformer according to the present invention to a backlight device. Although the transformer  80  shown in  FIG. 9  is used as an example in  FIG. 10 , the structure in the case of applying the transformers  40  to  60  to the backlight device is similar to the foregoing. 
     Referring to  FIG. 10 , according to the third embodiment, the transformer  80  may be preferably attached and held to a reflecting plate  24  as a component of the backlight device. The reflecting plate  24  is structured by attaching a reflecting sheet to a metallic frame or resin frame, and a plurality of holes for positioning the bobbin  1  are arranged at predetermined positions of the reflecting plate  24 . Further, an attaching hook  22  is integrally formed to the terminal base  3 B on the side surface of the terminal base  3 B of the bobbin  1 , the attaching hook  22  is also integrally formed to the terminal base  4 A on the side surface of the terminal base  4 A, and the attaching hooks  22  are positioned on a diagonal line of the bobbin  1 . In the bobbin  1 , the forming position of the attaching hook  22  and the number of the attaching hooks  22  are not limited to the foregoing and the attaching hooks  22  may be arranged on another diagonal line (of the terminal bases  3 A and  4 B) or to two or more positions. Further, the attaching hooks  22  may be arranged independently of the bobbin  1 . 
     In the transformer  80 , the attaching hooks  22  arranged to the bobbin  1 , leads  23   a  to  23   d , and bosses  19  (refer to  FIGS. 3 and 4 ) are inserted into corresponding holes formed to the reflecting plate  24 , thereby being positioned on the reflecting plate  24 . In this case, a return portion  22   a  is formed at an edge portion of the attaching hook  22 , and the transformer  80  is attached and held onto the reflecting plate  24  by the return portion  22   a . Further, a boss  25  formed the reflecting plate  24  becomes a receiving portion of a printed circuit board  26  having a backlight drive circuit (inverter), and is used for fixing the printed circuit board  26  to the reflecting plate  24  with a screw  27  by using a screw hole formed to the boss  25 . The lead  23   a  to  23   d  are inserted and soldered to through-holes  26   a  formed onto a pattern of the printed circuit board  26 . In the transformer  80 , the leads  23   a  to  23   d  are integrated into terminal pins  14   a  to  14   d , and an output signal from the backlight drive circuit is input to the primary winding  10  via the lead  23   b  and terminal pin  14   b  and the lead  23   c  and terminal pin  14   c . The backlight device can be preferably used for a liquid crystal display apparatus such as a liquid crystal TV apparatus. 
     Herein, in a conventional backlight device  100  shown in  FIG. 11 , the inverter substrate  112  is attached to a substrate attaching portion of a metallic frame or resin frame. At the substrate attaching portion, in association with the operation of the backlight device  100 , heat generation from the cold cathode lamps  110  or the inverter substrate  112  causes contraction and expansion, and an expansion coefficient thereof is much higher than an expansion coefficient of the cold cathode lamp  110  containing glass. However, in the backlight device  100 , the inverter substrate  112  is connected to the cold cathode lamp  110   s  via lamp cables  110   a , and the cold lamp cable  110  absorbs the difference of the contraction and expansion between the substrate attaching portion and the cold cathode lamp  110 , thereby preventing the break of the cold cathode lamp  110 . 
     In this view point, the transformer  80  according to the present invention is similarly attached to the reflecting plate  24  containing a metallic frame or resin frame, and the cold cathode lamp  70  is directly connected to the bobbins  1  at both ends thereof. However, the lamp connecting terminal  17  to which the electrodes  70   a  at both ends of the cold cathode lamp  70  are connected has elasticity caused by the bending portion  17   a . The elastic deformation of the bending portion  17   a  of the lamp connecting terminal  17  absorbs the difference of the contraction and expansion between the reflecting plate  24  and the cold cathode lamp  70 , and the break of the cold cathode lamp  70  is prevented without using the above-mentioned lamp cable. 
     The embodiments of the present invention have been described with reference to  FIGS. 1 to 10 . However, the transformer according to the present invention is not limited to the structures as shown and described above. For example, as long as the lamp connecting terminal  17  has the elasticity, the bending portion  17   a  of the lamp connecting terminal  17  is not limited to the shape thereof. Alternatively, the terminal bases  3  and  4  in which the lamp connecting terminal  17  is implanted may have the elasticity. Further, the cold cathode lamp can be accommodated and held, not to the bottom surfaces of the terminal bases  3  and  4 , but to the side surfaces thereof. Furthermore, the reflecting plate  24  is attached to the bobbin  1  by the attaching hook  22  in  FIG. 10 . However, a projected portion for attachment may be formed to the bottom surface of the bobbin  1 , and the projected portion for attachment may be pressed into a hole formed to the reflecting plate  24 , thereby attaching the bobbin  1  to the reflecting plate  24 . Moreover, in the transformer according to the present invention, the core  11  may be any of an EE core, U-I core, and core obtained by combining I shape and squared shape.