Patent Publication Number: US-5898354-A

Title: Molding structure for flyback transformer

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a molding structure for a flyback transformer, and in particular to an improved molding structure for a flyback transformer which is capable of easily molding a bobbin having coils wound thereon in the interior of a casing using an epoxy resin, etc. 
     2. Description of the Conventional Art 
     As shown in FIG. 1, in the bobbin structure of a conventional flyback transformer, a plurality of ribs 3 are co-centrally protruded from an outer circumferential surface of a basic bobbin portion 1a at a predetermined interval. 
     A low voltage coil (hereinafter called a primary coil) 2 is wound on an outer surface of a basic bobbin portion la between the ribs 3. 
     In addition, a film guide 5 having a predetermined height which is higher than that of each rib 3 is formed at both ends of the basic bobbin portion 1a. 
     An insulation film 6 having a predetermined width corresponding to the longitudinal distance of the basic bobbin portion 1a is wound on the outer surfaces of the primary coil 2 and the ribs 3. A high voltage coil (hereinafter called a secondary coil) is wound on the upper surface of the insulation film 6. 
     At this time, more than one insulation film and secondary coil may be wound on the upper surface of the secondary coil 4, respectively. 
     As shown in FIG. 2, there are provided a ferrite core insertion member 13 having a core contact surface 14 formed in one side thereof and an insertion portion 11 formed in the center thereof. The ferrite core insertion member 13 is formed at an end portion of the bobbin 1, namely, on the upper end portion of the coil portion 10. 
     When a channel-shaped ferrite core 15, which is used for inducing a secondary voltage based on the primary voltage, is inserted into the ferrite core insertion portion 11 of the ferrite core insertion member 13, a recessed portion 15a of the core 15 contacts with the core contact surface 14. 
     In addition, as shown in FIG. 3, the coils 2 and 4 and the bobbin 1 are inserted into the casing 20 in order to enable an insulation and to prevent a leakage and discharge of a high voltage, and the casing 20 and the portion between the coils and bobbin (namely, a casing space portion) are molded using an epoxy resin, etc. A lead connection portion 17b is formed at one end (namely, at the opposite portion of the portion in which the ferrite core insertion member 13 is formed) of the casing 20 into which the bobbin 1 is inserted. 
     A high voltage lead 17 is connected with a high voltage terminal 17a formed in the interior of the bobbin 1 and is inserted into the lead connection portion 17b for supplying a high voltage of an anode to the Braun tube. 
     At this time, when molding the casing space portion using the epoxy resin 19, a rubber bushing 18 tightly contacting with the high voltage lead 17 is engaged to the upper portion of the lead connection portion 17b, into which the high voltage lead 17 is inserted, in a shape that the upper portion of the lead connection portion 17b is surrounded so that the epoxy resin 19 is not leaked to the outside of the casing 20 in the interior of the lead connection portion 17b. 
     After the molding operation is completed, as shown in FIG. 2, the ferrite core 15 is engaged to the ferrite core insertion member 13 for thereby fabricating a flyback transformer. 
     In the drawings, reference numeral 16 denotes a resin which is leaked to the outside. 
     However, when fabricating the conventional flyback transformer, the casing space portion is molded using the epoxy resin, etc. Therefore, a predetermined gas and gas bubbles are generated due to a high temperature molding operation, so that the epoxy resin is not uniformly formed in the space portion of the casing due to the gas and bubbles. 
     Namely, since the casing is sealed, the epoxy resin which is provided into the interior of the casing receives a repulsive force of the air in the interior of the casing. The above operation will be explained in more detail. For example, when inserting a piston into a cylinder, since there are not any holes for exhausting the air in the cylinder to the outside, a predetermined force is generated with respect to the supply of the epoxy resin in the cylinder. Therefore, the epoxy resin is not uniformly formed between the coils and the insulation film. Due to the above-described problems, it is impossible to enable a desired insulation between coils. 
     In addition, when a molding operation is performed using the epoxy resin, since the epoxy resin, which is overflown, is formed on the upper surface of the core contact surface, when the core is inserted into the bobbin, the thusly overflown resin contacts with the recessed portion, so that the ferrite core may not be installed at the normal position due to the height of the overflown resin, and the electric characteristic of the product may be changed. In addition to that, a predetermined problem may occur when engaging the core. 
     Furthermore, in order to prevent the epoxy resin from being leaked to the outside of the casing, since a rubber bushing is additionally used, the number of fabrication processes is increased. The rubber bushing may be extended during a high temperature process and may be escaped from the lead connection portion, so that the resin may be leaked to the outside. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a molding structure for a flyback transformer which overcomes the problems encountered in the conventional art. 
     It is another object of the present invention to provide a molding structure for a flyback transformer which is capable of easily removing gas, which is generated when molding the bobbin on which coils are wound, to the outside of a casing. 
     It is another object of the present invention to provide a molding structure for a flyback transformer which is capable of preventing the mounting position of a core from being moved to the normal position due to the epoxy resin which is overflown on a core contact surface when molding the bobbin using an epoxy resin. 
     It is another object of the present invention to provide a molding structure for a flyback transformer which is capable of preventing the leakage of an epoxy resin by forming a predetermined shaped protrusion, which tightly contacts with a high voltage lead, on an inner circumferential surface of a lead connection portion formed on the upper surface of the casing without additionally using the rubber bushing. 
     In order to achieve the above objects, there is provided a molding structure for a flyback transformer which includes a basic bobbin member having a primary coil wound on an outer circumferential surface thereof, a film guide formed on both end portions of the basic bobbin member and having a gas exhaust holes, said film guide supporting more than one insulation film wound on an outer circumferential surface of the primary coil and more than one secondary coil, a bobbin including a ferrite core insertion member having a resin receiving space portion, and a casing receiving the bobbin therein and having a lead connection portion having a lead connection portion protrusion formed on an inner circumferential surface, wherein a high voltage lead is inserted into the upper portion of the casing. 
     Additional advantages, objects and features of the invention will become more apparent from the description which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
     FIG. 1 is a cross-sectional view illustrating a bobbin structure for a conventional flyback transformer; 
     FIG. 2 is a partially cut-away perspective view illustrating the construction that a bobbin is molded by an epoxy resin and a ferrite core is inserted into a ferrite core insertion portion in the molding structure of a conventional flyback transformer; 
     FIG. 3 is a partially cut-away cross-sectional view illustrating the portion into which a high voltage lead is inserted in the leakage prevention structure for the molding structure of a conventional flyback transformer; 
     FIG. 4 is a cross-sectional view illustrating a gas exhausting structure formed in a bobbin of a molding structure of a flyback transformer according to the present invention; 
     FIG. 5 is a partially cut-away perspective view illustrating the construction before a ferrite core of a molding structure of a flyback transformer according to the present invention is inserted; 
     FIG. 6 is a partial cross-sectional view illustrating the construction after a ferrite core of a molding structure of a flyback transformer according to the present invention is inserted; and 
     FIG. 7 is a partial cross-sectional view illustrating the portion into which a high voltage lead is inserted in a leakage prevention structure for the molding structure of a flyback transformer according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The flyback transformer according to the present invention will be explained with reference to the accompanying drawings. 
     As shown in FIG. 4, in the molding structure of a flyback transformer according to the present invention, a plurality of ribs 23 are formed at a regular interval on an outer circumferential surface of a hollow basic bobbin portion 21a in the circumferential and longitudinal directions. 
     A primary coil 2 is wound on an outer circumferential surface of the basic bobbin portion 21a between the ribs 23 in the circumferential direction. 
     In addition, spaced-apart film guides 25 which are longer than that of the rib 23 are formed at both ends of the bobbin. The film guides 25 have step portions 25a. The upper and lower ends of the insulation film 26 contact with the step portions 25a. 
     Therefore, the upper and lower ends of the insulation film 26 are correctly engaged with the bobbin 21. In addition, since the step portions 25a of the film guide 25 support the upper and lower ends of the insulation film 26, the insulation film 26 is co-centrally wound together with a secondary coil 24. 
     An insulation film 26 having the width corresponding to the longitudinal distance of the basic bobbin portion 21a tightly contacts with the upper portions of the ribs 23 and the step portions 25a of the film guide 25, respectively. A secondary coil 24 is wound on the upper surface of the insulation film 26. 
     At this time, more than one insulation film and the secondary coil may be repeatedly wound on the upper surface of the secondary coil 24. 
     As shown in FIG. 5, a ferrite core insertion member 43 having a receiving space portion 44 formed in one side and an insertion portion 41 of a ferrite core formed in the center thereof is formed on the upper portion of the coil portion 50. 
     The thusly constituted flyback transformer bobbin is inserted into the casing 40, and the portion between the casing 40 and the coil-bobbin (casing space portion) is molded using an epoxy resin. In addition, as shown in FIGS. 5 and 6, the ferrite core 45 is inserted into the ferrite core insertion member 43 for thereby fabricating a flyback transformer according to the present invention. 
     As shown in FIG. 7, a high voltage lead 54 coated with a rubber on its outer surface is inserted into the lead connection portion 53 formed on the upper portion of the casing 40, and the high voltage lead 54 contacts with the high voltage terminal 57a formed in the bobbin 21. 
     In another embodiment of the molding structure of the flyback transformer according to the present invention, as shown in FIG. 4, more than one gas exhausting hole 27 are formed in the film guide 25 for exhausting the gas generated when molding the casing and the coil-bobbin (casing space portion) using an epoxy resin, etc. 
     Therefore, the gas and gas bubbles generated when a high temperature epoxy resin is flown into the interior of the casing 40 are exhausted to the outside of the casing 40 through the gas exhausting holes 27, so that it is possible to prevent a predetermined air pressure in the casing 40 from acting as a force repulsive to the supply of the epoxy resin. 
     Namely, since the gas and gas bubbles generated during the molding operation are exhausted to the outside of the casing 40 through the gas exhausting hole 27, the repulsive force which interrupts the supply of the epoxy resin is decreased, so that the epoxy resin is uniformly formed between the coils 22 and 24 and the insulation film 26. In addition, the gas bubbles generated due to the gas do not exist in the interior of the casing 40 after completing the epoxy resin molding operation. 
     In the molding structure of the flyback transformer according to the present invention, as shown in FIG. 5, a ferrite core insertion member 43 having a receiving space portion 44 which receives the resin 46 overflown during the epoxy resin molding operation is formed in the upper surface of the coil 50. 
     At this time, a core contact step 47 and a plurality of core contact protrusions 48 are formed on the upper surface of the receiving space portion 44 for serving as a ferrite core support portion and thereby supporting the recessed portion 45a of the core 45 when a channel-shaped ferrite core 45 is inserted into the interior of the coil portion 50. 
     In more detail, a plurality of core contact protrusions 48 are formed in one side of the ferrite core insertion portion 41 on the upper surface of the receiving space portion 44. Each core contact protrusion 48 has a predetermined height and contacts with one end portion of the recessed portion 45a of the ferrite core 45, and a core contact step 47 is formed on an upper surface of the receiving space portion 44 and contacts with the recessed portion 45a of the ferrite core 45 at a predetermined distance from the core contact protrusion 48. 
     Therefore, when the ferrite core 45 is inserted into the ferrite core insertion portion 41, as shown in FIG. 6, the recessed portion 45a of the ferrite core 45 does not contact with the bottom of the receiving space portion 44. Namely, it contacts with the core contact protrusion 48 and the upper surface of the core contact step 47, respectively. 
     Therefore, even when the resin 46 is overflown to the upper surface of the receiving space portion 44 when molding the epoxy resin, since the recessed portion 45a of the ferrite core 45 supportedly contacts with the core contact step 47 and the upper surface of the core contact protrusion 48, respectively, when the ferrite core 45 is engaged to the bobbin 21, the ferrite core 45 is supported by the core contact protrusion 48 and the core contact step 47 irrespective of the overflow of the resin 46, so that the ferrite core 45 is correctly engaged to the receiving space portion 44 of the bobbin 21. 
     In addition, in the molding structure of a flyback transformer according to the present invention, a lead connection portion 53, into which a high voltage lead 54 is inserted as shown in FIG. 7, is formed in one end portion of the casing 40 (namely, in the portion opposite to the portion in which the ferrite core insertion member is formed). 
     At this time, the lead connection portion protrusion 53a is circumferentially formed on an inner surface of the lead connection portion 53, into which the high voltage lead 54 is inserted, so that the resin 46a is not leaked to the outside of the casing 40 through the interior of the lead connection portion 53 when molding the epoxy resin 46. 
     As shown in FIG. 7, the height 53b of the lead connection portion protrusion 53a has a predetermined thickness so that the lead connection portion protrusion 53a contacts with the rubber coated on the outer circumferential surface of the high voltage lead 54, and the diameter of the lead connection portion protrusion 53a is slightly smaller than the outer diameter of the high voltage lead 54 so that a stronger surface contact is enabled when the rubber portion is expanded due to the high temperature epoxy resin. 
     In more detail, the high voltage lead 54 is inserted into the interior of the lead connection portion 53 and contacts with the lead connection portion protrusion 53a for thereby being connected with the terminal 57a. In this state, the epoxy resin having a temperature 90° C. through 110° C. is provided into the casing 40, so that the rubber of the high voltage lead 54 is expanded in the circumferential direction. 
     Therefore, since the rubber of the high voltage lead 54 strongly contact with the inner circumferential surface of the lead connection portion protrusion 53a, the resin 46a is not leaked through the opening 53c of the high voltage lead connection portion. Namely, it is sealed within the casing 40. 
     In FIG. 7, the broken line represents the diameter of the high voltage lead 54 in a state that the rubber is not expanded, and the full line represents the diameter of the high voltage lead 54 in a state that the rubber is expanded. 
     As described above, the molding structure of the flyback transformer according to the present invention is capable of easily and uniformly forming the epoxy resin. Since the gas bubbles are effectively removed, the insulation efficiency is increased. It is possible to prevent an electric characteristic variation due to the gas bubbles. A good quality flyback transformer may be manufactured. 
     In addition, the ferrite core is correctly formed by preventing an incorrect mounting of the ferrite core due to the overflown resin for thereby ensuring a stable electric characteristic. 
     Since a rubber bushing is not additionally used for preventing the leakage of an epoxy resin, the number of fabrication and parts is decreased for thereby increasing the productivity. 
     Although the preferred embodiment of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as recited in the accompanying claims.