Abstract:
To greatly improve the productivity, the general versatility, the downsizing, the performance and the like, as compared to those of the conventional transformer, provided is a transformer including: a core; a primary winding; a secondary winding; a bobbin provided with a low voltage side coil winding portion and a high voltage side coil winding portion, wherein the secondary winding is wound onto each of the coil winding portions; and a casing disposed so as to cover an outer periphery of the bobbin, wherein the primary winding is wound onto a portion of an outer periphery of the casing corresponding to a position of the low voltage side coil winding portion.

Description:
TECHNICAL FIELD 
     The present invention relates to a transformer for use in, for example, a circuit for lighting a vehicle headlamp using a metal halide lamp or a circuit for converting a high voltage to a low voltage. 
     BACKGROUND ART 
     Conventionally, when a high voltage discharge lamp (for example, metal halide lamp) which needs a high voltage at startup is used as a vehicle headlamp, a high voltage transformer which outputs a high voltage have been used, as disclosed in Japanese Laid-open Patent Application Publication No. 8-130127 (Patent Literature 1), for example. 
     The conventional high voltage transformer, as disclosed in Japanese Laid-open Patent Application Publication No. 8-130127 (Patent Literature 1), is constituted by a core, a hollow cylindrical shaped spool into the hollow portion of which the core is inserted, a secondary winding wound around the outer periphery of the spool, a casing made of a resin covering the spool being wound with the secondary winding, and a primary winding being inserted into the casing. The core, the spool and the secondary winding are housed in the casing, covered with a filled resin, and are fixed and integrated. Further, it is disclosed in Japanese Laid-open Patent Application Publication No. 8-130127 (Patent Literature 1) that by inserting the both ends of the primary winding being disposed on the casing of a printed circuit board, the core, the spool, the secondary winding, the casing and the printed circuit board are integrated, and the high voltage transformer is configured. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Laid-open Patent Application Publication No. 8-130127 
     SUMMARY OF INVENTION 
     Technical Problem 
     As described above, with regard to the structure in which the casing is inserted to the printed circuit board and secured integrally by filling the resin material into the space between the outer periphery of the spool and the inner surface of the casing, like the transformer as known in Japanese Laid-open Patent Application Publication No. 8-130127 (Patent Literature 1), the positions of the through-holes are different depending on the arrangement of the circuit and the like of the printed circuit board, and so there is a problem that general versatility is lacked. 
     In addition, because a work of filling the resin material into the space between the outer periphery of the spool and the inner surface of the casing is required, the assembling work grows complicated, the working man-hours increase, and further, some waiting time for curing of the filled resin material is needed. Therefore, there is a problem that productivity grows poor as a whole and cost increase is induced. 
     Thus, the present invention has been made in view of the above described problems, and the object of the present invention is to provide a transformer that can greatly improve the productivity, the general versatility, the downsizing, the performance and the like, as compared to those of the conventional transformer. 
     Solution to Problem 
     In order to achieve the above described object, a transformer according to the present invention comprises: a core; a primary winding; a secondary winding; a bobbin provided with a low voltage side coil winding portion and a high voltage side coil winding portion, wherein the secondary winding is wound onto each of the coil winding portions; and a casing disposed so as to cover an outer periphery of the bobbin, wherein the primary winding is wound onto a portion of an outer periphery of the casing corresponding to a position of the low voltage side coil winding portion. 
     According to the configuration, the transformer can be formed by covering the outer periphery of the bobbin onto which the secondary winding is wound, with the casing, and winding the primary winding onto the portion of the outer periphery of the casing corresponding to the position of the low voltage side coil winding portion. In this way, by winding the primary winding to the portion overlapping with the low voltage side winding of the secondary winding, the parasitic capacitance generated in the high voltage side winding of the secondary winding by the primary winding can be reduced. Accordingly, the electric power loss at high frequencies can be reduced. Further, because the energy stored in the parasitic capacitance increases with increasing potential between the primary winding and the secondary winding, it is possible to reduce the energy stored in the parasitic capacitance, and thereby reduce the electric power loss due to leakage current at high frequencies, by winding the primary winding over the outer periphery of the low voltage side coil winding of the secondary winding. In addition, insulation properties between the primary winding and the secondary winding can be assured. 
     In the above described configuration, a configuration can be employed where the secondary winding is a high voltage winding and the primary winding is a low voltage winding, and the primary winding is placed and wound in a portion corresponding to an area between the both ends of the low voltage side coil winding portion. 
     According to the configuration, by placing the primary winding in the portion corresponding to the region between the both ends of the low voltage coil winding portion and winding the primary winding therein, the distance between the high voltage side coil winding of the secondary winding and the low voltage side coil winding of the secondary winding, and the distance between the low voltage side coil winding of the secondary winding and the primary winding can be gotten closer. Accordingly, the coupling coefficient grows larger and so a high coupling is obtained. In addition, the length of the transformer in the longitudinal direction can be shortened by winding the primary winding onto the outer periphery of the casing. 
     In the above described configuration, a configuration can be employed where the casing is formed in a hollow box-shaped body provided with an opening on a lower surface of the outer periphery thereof for receiving and accommodating the bobbin therein, and the opening has a retaining protrusion to engage the accommodated bobbin. 
     According to the configuration, by covering the bobbin with the casing from the upper side of the bobbin and accommodating the bobbin to a predetermined position in the case from the opening of the outer periphery lower surface of the casing, the bobbin is covered with the casing and the retaining protrusion engages the bobbin, and then the bobbin and the casing are fixed together. Thereby, the work of filling an insulation resin or the like between the casing and the bobbin and of fixing the bobbin and the casing becomes unnecessary. In addition, in a case the bobbin is accommodated in the casing from the terminal block portion side in the longitudinal direction of the bobbin, it is necessary to provide an opening having a size capable of passing the terminal block portion attached to the bobbin, and so the overall size of the casing grows larger. However, as disclosed in this configuration, in the case the opening is provided to the lower surface of the casing and the bobbin is covered with the casing from the upper side of the bobbin, it is enough to provide an opening having at least a size of the outer diameter of the bobbin and so the size of the bobbin can be reduced. 
     In the above described configuration, a configuration can be employed where the casing is provided with an insulation tape onto the outer periphery thereof where the primary winding is wound. 
     According to the configuration, insulation properties between the primary winding wound onto the outer periphery of the casing and the secondary winding wound onto the outer periphery of the bobbin can be assured by the insulation tape. 
     In the above described configuration, a configuration can be employed where the core comprises an I type magnetic body core and a C type magnetic body core. 
     According to the configuration, the I type magnetic material core and the C type magnetic material core form a closed magnetic circuit and so the magnetic flux leakage can be reduced. 
     Advantageous Effects of Invention 
     According to the present invention, the bobbin and the casing are integrated by covering the outer periphery of the bobbin onto which the secondary winding is wound, with the casing, and winding the primary winding onto the portion of the outer periphery of the casing corresponding to the position of the low voltage side coil winding portion. As a result, for assuring the insulation properties between the secondary winding and the primary winding, the resin material which has been filled into the space between the secondary winding and the primary winding conventionally can be omitted and the work can be simplified, and so it becomes possible to promote reduction of man-hours of the work and to expect increase of productivity. In addition, because the coupling coefficient between the secondary winding and the primary winding grows larger and so a high coupling can be obtained, by getting closer the distance between the secondary winding and the primary winding, the higher performance can be expected. 
     Further, in the present invention, the casing and the bobbin are configured to be fixed and secured, by attaching the casing so as to cover the bobbin. This is different from the conventional transformer in which the casing and the bobbin are integrated by using through-holes and the like of the printed circuit board side. As a result, a product having general versatility is obtained without depending on the shape of the printed circuit board and the like. Accordingly, further improvement of productivity, simplification of the shape, downsizing and the like can be expected. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an external perspective view of a transformer according to one embodiment of the present invention, viewed from the front side obliquely upward direction. 
         FIG. 2  is an external perspective view of the transformer according to one embodiment of the present invention, viewed from the rear side obliquely upward direction. 
         FIG. 3  is an enlarged plan view of the transformer according to one embodiment of the present invention, viewed from the lower side direction. 
         FIG. 4  is a line A-A schematic longitudinal sectional view of  FIG. 2 . 
         FIG. 5  is a line B-B schematic longitudinal sectional view of  FIG. 4 . 
         FIG. 6  is an exploded perspective view for explaining a state before attaching a casing to a bobbin of the transformer according to one embodiment of the present invention. 
         FIG. 7  is an explanatory view for explaining a state in which the casing is attached to the bobbin of the transformer according to one embodiment of the present invention. 
         FIG. 8  is a schematic longitudinal sectional view showing a transformer according to another embodiment of the present invention. 
         FIG. 9  is a line C-C schematic longitudinal sectional view of  FIG. 8 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as “embodiment”) shall be described in detail with reference to the accompanying drawings. 
       FIG. 1  and  FIG. 2  illustrate a transformer according to one embodiment of the present invention.  FIG. 1  is an external perspective view of the transformer, viewed from the front side obliquely upward direction.  FIG. 2  is an external perspective view of the transformer, viewed from the rear side obliquely upward direction.  FIG. 3  is an enlarged plan view of the transformer, viewed from the lower direction.  FIG. 4  is a line A-A schematic longitudinal sectional view of  FIG. 2 .  FIG. 5  is a line B-B schematic longitudinal sectional view of  FIG. 4 . In addition, The X-X direction of  FIG. 1  is described as longitudinal direction, the Y-Y direction of  FIG. 1  is described as horizontal direction and the Z-Z direction of  FIG. 1  is described as vertical direction, 
     A transformer  10  in  FIG. 1  to  FIG. 5  is an example of the high voltage transformer, and is configured by a core  11 , a bobbin  12 , a secondary winding  13  being wound onto the outer periphery of the bobbin  12 , a casing  14  provided so as to cover the outer periphery of the bobbin  12 , a primary winding  15  being wound onto the outer periphery of the casing  14  and the like. In addition, though the high voltage transformer is referred to as an example in this embodiment, the present invention is not limited to the high voltage transformer, but can be applied to general transformers widely. 
     The core  11  is an I type magnetic material core in a form of a rectangular parallelepiped, and is made of a ferrite material for example. 
     The bobbin  12  is made of a resin. As shown in detail in  FIG. 4  to  FIG. 7 , the bobbin  12  is provided inside with a hollow portion  16  extending through longitudinally for accommodating and placing the core  11 , and is formed integrally with a hollow main body  12   a  of a substantially cylindrical shape formed in a rectangular cross-sectional shape, and terminal blocks  12   b ,  12   c  which are provided at the front end and the rear end of the hollow main body  12   a , respectively. 
     On the outer periphery portion of the hollow main body  12   a , a low voltage side coil winding portion  17  that is formed by winding a low voltage side coil winding  13   a  (hereinafter referred to as “low voltage side coil winding  13   a ”) of the secondary winding  13  which functions as a high voltage winding of the transformer  10 , by a predetermined number of turns, and a high voltage side coil winding portion  18  that is formed by winding a high voltage side coil winding  13   b  (hereinafter referred to as “high voltage side coil winding  13   b ”) of the secondary winding  13 , by a predetermined number of turns, so that the winding starts from the end of the low voltage side coil winding portion  17 , are arranged longitudinally in order. Further, on the outer periphery of the hollow main body  12   a , a partition between the low voltage side coil winding portion  17  and the high voltage side coil winding portion  18 , and a plurality of flange-like partition plate sections  19  which partition each of the inside of the low voltage side coil winding portion  17  and the high voltage side coil winding portion  18  into a plurality of sections, are provided integrally, at a distance from each other longitudinally. 
     The terminal block portion  12   b  is formed integrally with the hollow main body  12   a  in a state so that protrude toward outward forward direction longitudinally from the lower side of the hollow main body  12   a  in the low voltage side coil winding portion  17 . The terminal block portion  12   c  is formed integrally with the hollow main body  12   a  in a state so that protrude toward outward forward direction longitudinally from the lower side of the hollow main body  12   a  in the high voltage side coil winding portion  18 . In addition, in molding the bobbin  12 , terminals  20   a ,  20   b ,  20   c  are provided to the terminal block portion  12   b  by insert molding and terminals  20   d ,  20   e ,  20   f  are provided to the terminal block portion  12   c  by insert molding. 
     As shown in detail in  FIG. 4  to  FIG. 7 , the casing  14  is a resin molded body with a hollow portion inside and is attached to the bobbin  12  so as to cover the upper surface, the left and the right side surfaces in the horizontal direction and the front and the rear end surfaces in the longitudinal direction of the hollow main body  12   a . On the lower surface of the casing  14 , an opening  21  is provided for inserting the bobbin  12  into the inside. 
     Further, the opening  21  is provided with a plurality of retaining protrusions  22  of a claw shape on each of the left and right side surfaces. When the bobbin  12  is inserted to a predetermined position in the casing  14 , the bobbin  12  is secured to the lower surface of the partition plate section  19 , and is fixedly held and retained in the casing  14  by the retaining protrusions  22 . 
     On the front end portion and the rear end portion of the outer periphery surface of the casing  14  onto which the primary winding  15  is to be wound which functions as the low voltage winding of the transformer  10 , a front side partition plate section  23   a  and a rear side partition plate section  23   b  are formed, respectively. 
     An intermediate partition plate section  23   c  is provided at a position substantially corresponding to the position of a partition plate section  19  which partitions between the low voltage side coil winding portion  17  and the high voltage side coil winding portion  18  being formed on the outer periphery of the hollow main body  12   a  in the bobbin  12  (the partition plate section  19  at the location pointed to by the arrow K in  FIG. 4  and  FIG. 6 ). The outer periphery surface of the casing  14  between the rear side partition plate section  23   b  and the intermediate partition plate section  23   c  is filled. 
     Then, by winding the primary winding  15  over all the outer periphery region between the front side partition plate section  23   a  and the intermediate partition plate section  23   c , the both end portions of the primary winding  15  are fitted in position with the both end portions of the low voltage side coil winding  13   a  being wound to the low voltage side coil winding portion  17 , and the primary winding  15  is wound in a state being overlapped with the low voltage side coil winding  13   a.    
     Next, an example of the assembling procedure for the transformer  10  configured as above shall be explained. First, the low voltage side coil winding  13   a  of the secondary winding  13  is wound onto the low voltage side coil winding portion  17  of the bobbin  12 , and following the low voltage side coil winding  13   a , the high voltage side coil winding  13   b  of the secondary winding  13  is wound onto the high voltage side coil winding portion  18 . In addition, at this time, the coil end of the low voltage side coil winding  13   a  is bound to the terminal  20   c , and the coil end of the high voltage side coil winding  13   b  is bound to the terminal  20   d . Further, if necessary, each of the coil ends and the terminals  20   c ,  20   d  are fixed by using a solder or the like. 
     Then, as shown in  FIG. 6 , the case  14  is covered over the bobbin  12  from the upper side onto which the low voltage side coil winding  13   a  and the high voltage side coil winding  13   b  are wound, and the hollow main body  12   a  of the bobbin  12  is inserted into the inside of the casing  14 . When the bobbin  12  is inserted to a predetermined position in the casing  14 , the engaging claws  22  of the opening  21  are secured to the lower surface of the partition plate section  19 , the case  14  and the bobbin  12  are fixedly held each other and are integrated, in a state where the case  14  covers the upper surface, the left and the right side surfaces, and the front and the rear end surfaces.  FIG. 7  illustrates a state immediately after the casing  14  and the bobbin  12  are integrated. 
     Subsequently, onto the position of the casing  14  on which the primary winding  15  is to be wound, that is the outer periphery portion corresponding to the region between the front side partition plate section  23   a  and the intermediate partition plate section  23   c , an insulation tape  24   a  is wound by at least one turn, so that the insulation properties between the secondary winding  13  and the primary winding  15  to be wound thereafter are assured. 
     Then, the primary winding  15  is wound by a predetermined number of turns on the periphery region between the front side partition plate section  23   a  and the intermediate partition plate section  23   c  of the casing  14 , and the coil ends are bound and connected to each of the terminal  20   a  and the terminal  20   b . Further, if necessary, each of the coil ends and the terminals  20   a ,  20   b  are fixed by using a solder or the like. After the completion of the processing of the coil ends of the primary winding  15 , an insulation tape  24   b  is would by at least one turn from the outside of the primary winding  15  so as to cover the outer periphery surface of the primary winding  15 , and thereby a short-circuit of the primary winding  15  due to contact with external parts and the like is prevented. In this way, assembling is completed. 
     Accordingly, with regard to the transformer  10  configured in this way, by covering the bobbin  12  onto which the secondary winding  13  is wound with the casing  14  from the upper side of the bobbin  12  and accommodating the bobbin  12  to a predetermined position in the casing  14  from the side of the opening  21  of the casing  14 , the hollow main body  12   a  is covered with the casing  14 , and the engaging claw  22  of the casing  14  engages and retains the bobbin  12 , and the bobbin  12  and the casing  14  can be easily fixed together and integrated. Therefore, the work of filling the insulation resin between the casing  14  and bobbin  12  which has been performed in a conventional configuration of the transformer for fixing the bobbin and the casing grows unnecessary. 
     Further, when accommodating the bobbin  12  in the casing  14 , in the case the opening  21  is provided to the lower surface of the casing  14  and the bobbin  12  is covered with the casing  14  from the upper side of the bobbin  12  as disclosed in the configuration of the present example, it is enough to provide an opening  21  having a size of at least the outer diameter of the bobbin  12 . As a result, the size of the bobbin  12  can be reduced, downsizing of the transformer  10  becomes possible, and an effect by the higher coupling coefficient can be obtained by getting closer the distance between the primary winding  15  and the secondary winding  13 . 
     Further, it is different from the configuration of the conventional transformer in which the casing and the bobbin are integrated by using through-holes and the like of the printed circuit board side, and so the shape does not depend on the printed circuit board and the like, and a shape configuration having general versatility can be employed. 
     Further, because the primary winding  15  is wound to the portion overlapping with the low voltage side winding  13   a  of the secondary winding  13 , fitting both ends of the primary winding  15  of to both ends of the low voltage side winding  13   a  of the secondary winding  13 , the parasitic capacitance generated in the high voltage side winding  13   a  of the secondary winding  13  by the primary winding  15  can be reduced. Thus, the electric power loss at high frequencies can be reduced. In addition, because the energy stored in the parasitic capacitance increases with increasing potential between the primary winding  15  and the secondary winding  13 , it grows possible to reduce the energy stored in the parasitic capacitance, and thereby reduce the electric power loss due to the leakage current at high frequencies, by winding the primary winding  15  over the outer periphery of the low voltage side coil winding  13   a  of the secondary winding  13 . Further, the primary winding  15  is wound onto the outer periphery of the casing  14  so as to overlap with the low voltage side coil winding  13   a  of the secondary winding  13 , and so the insulation properties between the primary winding  15  and the secondary winding  13  can be assured. 
     Further, by winding the primary winding  15  onto the outer periphery of the casing  14 , it grows possible to shorten the longitudinal length of the transformer, as compared to a type of the transformer where the primary winding and the secondary winding are wound on a same bobbin. In addition, according to experiments, the coupling coefficient for the type of the transformer where the primary winding and the secondary winding are wound on the same bobbin is about 0.55, whereas the coupling coefficient for the configuration of the present example where the primary winding  15  is wound onto the outer periphery of the casing  14  is about 0.9. Therefore, the coupling coefficient can be improved. 
       FIG. 8  and  FIG. 9  illustrate a transformer according to another embodiment of the present invention.  FIG. 8  is a schematic longitudinal sectional view of the transformer.  FIG. 9  is a line C-C schematic longitudinal sectional view of  FIG. 8 . 
     The transformer  10  shown in  FIG. 8  and  FIG. 9  has a configuration where the core is composed of the I type magnetic material core  11  and a C type magnetic material core  25 . The other configurations are the same as those of the transformer  10  as shown in  FIG. 1  to  FIG. 7 . Therefore, the same reference numerals are given to the same components, and the duplicated description is omitted. 
     In  FIG. 8  and  FIG. 9 , the inside width between both the end portions of the C type magnetic material core  25  is approximately equals to the distance between the outer surfaces in the longitudinal direction of the hollow main body  12   a  of the bobbin  12 . In addition, the C type magnetic material core  25  is disposed on the upper surface outside of the casing  14 , both the end portions thereof are inserted to the inside from each of through-holes  26   a ,  26   b  of the casing  14 , and are disposed in a state where the end portions are opposed and approximated to each of the I type magnetic material core  11 , and then the C type magnetic material core  25  and the I type magnetic material core  11  are configured to form a closed magnetic circuit. 
     In this way, in the transformer  10  in which the I type magnetic material core  11  and the C type magnetic material core  25  form the closed magnetic circuit, the leakage magnetic flux can be reduced further. 
     Further, though the transformer has been described as another embodiment which uses both the C type magnetic material core  25  and the I type magnetic material core  11 , the transformer can be configured by using only two pieces of the C type magnetic material cores, without using the I type magnetic material core  11 . Further, the C type magnetic material core can be configured not on the upper surface outside of the casing, but on the side surface outside of the casing. 
     Meanwhile, in the present embodiments, it has been described that the primary winding functions as a low voltage winding, and the secondary winding functions as a high voltage winding, but the input voltage can be applied to either the primary winding or the secondary winding, and the output voltage comes from the secondary winding or the primary winding respectively in that case. 
     As above, the present invention has been described with reference to the embodiments, but it is needless to say that the technical scope of the present invention is not limited to the scope described in the above embodiments. It is apparent to those skilled in the art that a variety of modifications or improvements other than the above can be made. 
     INDUSTRIAL APPLICABILITY 
     In the above described embodiments, the description has been made on the case where the present invention is applied to the high voltage transformer, but the present invention can be applied to a part having a winding other than the high voltage transformer. 
     REFERENCE SIGNS LIST 
       10  . . . transformer,  11  . . . core (I type magnetic material core),  12  . . . bobbin,  12   a  . . . hollow main body,  12   b  . . . terminal block portion,  12   c  . . . terminal block portion,  13  . . . secondary winding,  13   a  . . . low voltage side coil winding,  13   b  . . . high voltage side coil winding,  14  . . . casing,  15  . . . primary winding,  16  . . . hollow portion,  17  . . . low voltage side coil winding portion,  18  . . . high voltage side coil winding portion,  19  . . . partition plate section,  20   a  to  20   f  . . . terminals,  21  . . . opening,  22  . . . retaining protrusion (engaging claw),  23   a  . . . front side partition plate section,  23   b  . . . rear side partition plate section,  23   c  . . . intermediate partition plate section,  24   a  . . . insulation tape,  24   b  . . . insulation tape,  25  . . . core (C type magnetic material core),  26   a  and  26   b  . . . through-holes