Patent Publication Number: US-9899144-B2

Title: Resonant high current density transformer

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 104133675, filed in Taiwan, Republic of China on Oct. 14, 2015, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a resonant high current density transformer, and more particularly, to a reduced-sized resonant transformer capable of increasing power density and easy of automated processing. 
     Description of the Related Art 
     In power supply system for electronic products such as LCD TVs, a main type of transformers used is transformers with leakage inductance property (such as LLC transformer) that reduces switching loss and noise. 
     In TW Utility Patent Publication No. M333646 titled “Improvement of Leakage-Inductance-type Resonant Transformer”, the transformer mainly includes: an outer bobbin provided with a first through-hole and a first recessed hole; an inner bobbin fitted inside the first through-hole of the outer bobbin, the inner bobbin being provided with a second through-hole and a second recessed hole; a core assembly with a first core, a second core and a third core, wherein the first and second cores are disposed in the second through-hole of the inner bobbin and the third core is disposed in the first recessed hole of the outer bobbin and the second recessed hole of the inner bobbin. By fitting the inner bobbin into the first through-hole of the outer bobbin, the coils in a first winding region and the coils in a second winding region can be overlapped to increase coupling. In addition, since the outer bobbin is provided with the recessed hole, heat generated from the coils of the inner bobbin can be effectively dissipated. Further, by providing the third core in the recessed holes, magnetic lines are able to form a sub-loop that increases the leakage inductance. 
     In addition, in TW Patent Publication No. I416553 titled “LLC Transformer Structure”, the transformer includes: a first winding base including: a body with a first winding region and a plurality of single-slot second winding regions, the first winding region having a plurality of guide pins, and the plurality of single-slot second winding regions being disposed at either side of the first winding region, the body having a first sidewall and a second sidewall on two opposite sides, and each of the first and second sidewalls having an opening; and a first channel running through the body; a primary winding wound on the first winding region of the first winding base and connected to the plurality of guide pins; a plurality of secondary winding wound on the plurality of single-slot second winding regions of the first winding base; a cover having a second channel, the second channel being in communication with the openings of the first and second sidewalls when the cover and the first winding base are being assembled together; and a magnetic core assembly partly provided in the first channel of the first winding base and the second channel of the cover. 
     By providing a plurality of single-slot second winding regions for winding a plurality of secondary windings separately, the windings and magnetic paths can be modified, and the size of the transformer can be reduced. In addition, the problem with a lack of control of the leakage inductance in the conventional transformer due to an air gap formed between the primary and secondary windings during the assembly of the magnetic core assembly can be eliminated. 
     However, the above two transformer designs still present the following shortcomings: 
     1. Conventional LLC transformer are usually formed by winding traditional wires (enameled wires) on the primary and secondary sides, but in the case of high current output, multi-strand secondary winding structure are often used to achieve a higher current tolerance. However, with these winding structures with multi-strand wires (enameled wires), it can be difficult to strip off the insulation layers, there might also be difficulties in output wiring or wire twisting due to the large number of strands. Furthermore, gaps are created between wires (enameled wires), so the size of the transformer cannot be reduced. 
     2. In conventional LLC transformer structures, the primary and secondary windings are wound on different locations of a single bobbin (winding base), in addition to winding, interspersing insulation sleeves and twisting wires are labor intensive. 
     3. In conventional LLC transformer structures, there is an approach of using metal plates to replace the secondary winding. However, if the primary and secondary windings are provided on the same bobbin, distances associated with safety regulations may not be long enough, and leakage inductance cannot be easily modified, so an additional inductor is needed as a resonant inductor. On the other hand, if the primary and secondary windings are provided on the two bobbins, a constant distance between the two bobbins is difficult to maintain, which results in drifts in characteristics such as the leakage inductance. 
     In view of the shortcomings in the conventional transformer structures, the present invention is proposed to provide improvements that address these shortcomings. 
     SUMMARY OF THE INVENTION 
     One main objective of the present invention is to provide a resonant high current density transformer that uses metal plates in place of traditional wires (enameled wires) as the secondary winding to increase the effective conductive cross-sectional area in a unit area, thereby effectively reducing the size of the transformer. 
     Another objective of the present invention is to provide a resonant high current density transformer that allows the primary and secondary windings to be disposed on two separate bobbins, and the two bobbins fit onto the side posts on two sides of two cores. This enables easy assembly of each winding, increases processing efficiency, and also reduces the size of the transformer, thus realizing the characteristic of high power density. 
     Yet another objective of the present invention is to provide a resonant high current density transformer that allows the primary and secondary windings to be disposed on two separate bobbins. The two bobbins are fastened to each other by mechanical structures such as corresponding engaging slots and tenons. This effectively regulates the distance between the two bobbins, and controls the characteristics of the transformer such as the leakage inductance. 
     In order to achieve the above objectives and efficacies, the technical means employed by the present invention may include: two cores, each including first and second side posts extending in the same direction from two sides thereof, wherein the two cores abut against each other with the two first side posts facing each other and the two second side posts facing each other; a first bobbin provided with a penetrating first through-hole that envelops the first side posts on the same side of the two cores, wherein a side plate is provided on the outer periphery of either end of the first through-hole, and a spacer is provided on the first bobbin between the two side plates on the outer periphery of the first through-hole, and two coil slots are formed on the two sides of the spacer, respectively; a primary winding formed by winding wires around the two coil slots of the first bobbin; a second bobbin provided with a penetrating second through-hole that envelops the second side posts on the same side of the two cores, wherein the second bobbin is provided with a spacer on the mid-section of the outer periphery of the second through-hole, and two winding regions and are formed on the two sides of the spacer, respectively; two metal plates bent to envelop the outer peripheries of the winding regions and of the second bobbin to form a secondary winding; a bobbin mount disposed at the external flank of the second bobbin, the bobbin mount including a base provided with a barrier plate on a side closer to the first bobbin, wherein the barrier plate is used for separating the first and second bobbins; and an insulating “U-shape” separating cover provided on a side of the first bobbin closer to the bobbin mount, wherein the two ends of the separating cover cover the top and bottom sides of the first bobbin, respectively. 
     Based on the above structure, a lateral fastening groove is provided on a side of each side plate closer to the coil slot, whereas a lateral flap corresponding to each lateral fastening groove is provided on each of two lateral edges of the separating cover, and the separating cover is secured at the outer side of the coil slots of the first bobbin by inserting each lateral flap into the corresponding lateral fastening groove. 
     Based on the above structure, a first engaging tenon and a first engaging slot are provided on a side of the first bobbin closer to the bobbin mount, whereas a corresponding second engaging slot and a corresponding second engaging tenon are provided on a side of the bobbin mount closer to the first bobbin, and the bobbin mount and the first bobbin are joined together by inserting the first engaging tenon into the second engaging slot, and the second engaging tenon into the first engaging slot. 
     Based on the above structure, the first bobbin is provided with a first side retainer on each of the two side plates, and a first positioning recess is provided on a side of each first side retainer facing the first through-hole, whereas the base is provided with a second side retainer at each of the two ends thereof on a side away from the barrier plate, and a second positioning recess is provided on a side of each second side retainer facing the barrier plate, and the first and the second positioning recesses abut against two lateral edges of the two cores, respectively. 
     Based on the above structure, a plurality of terminals are provided on the first and the second side retainers. 
     Based on the above structure, the base is provided with a middle slot between the barrier plate and the second side retainers, and a side slot is provided on each of the two sides of the middle slot, whereas each of the metal plates include a lateral end and a middle end, and the middle ends of the metal plates both pass through the middle slot, while the lateral ends of the metal plates at different winding regions pass through different lateral slots. 
     Based on the above structure, a plurality of gaps are provided on the spacer of the first bobbin. 
     The objectives, efficacies and features of the present invention can be more fully understood by referring to the drawing as follows: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of the structure of the present invention. 
         FIG. 2  is an exterior view of the overall assembly of the present invention. 
         FIG. 3  is a cross-sectional view of the assembly of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1 to 3 , it can be understood that the structure of the present invention mainly includes: two cores  1 , a first bobbin  2 , a bobbin mount  3 , a second bobbin  4 , a separating cover  5 , a metal plate  6  and a primary winding  7 ; wherein first and second side posts  11  and  12  extending in the same direction from the two sides of each of the cores  1 . When the two cores  2  abut against each other with the two first side posts  11  facing each other and the two second side posts  12  facing each other, a magnetic loop is formed. 
     The first bobbin  2  is provided with a penetrating first through-hole  21 , which envelops the first side posts  11  on the same side of the two cores  1  at their outer peripheries. A side plate  22  is provided on the outer periphery of either end of the first through-hole  21 . A spacer  23  is provided between the two side plates  22 . Two coil slots  231  are formed on the two sides of the spacer  23 , respectively. A plurality of gaps  232  are provided on the spacer  23 . A lateral fastening groove  221  is provided on the side of each side plate  22  closer to the coil slot  231 , whereas a first side retainer  24  is provided on the side of each side plate  22  away from the coil slot  231 . A first engaging tenon  251  (e.g. a dovetail tenon) and a first engaging slot  25  (e.g. a dovetail slot) are provided on a side of the first bobbin  2  away from the first side retainers  24 . A plurality of terminals  242  are provided on the two first side retainers  24 . A first positioning recess  241  is provided on the side of each first side retainer  24  facing the first through-hole  21 ; in one possible embodiment, the first positioning recess  241  has an edge shape conforming to the side of the core  1  closer to the first side post  11 , such that the first positioning recess  241  conforms to and abuts against the side edge of the core  1  closer to the first side post  11  to facilitate positioning. 
     The primary winding  7  is formed by winding wires around each coil slot  231  of the first bobbin  2 , and the gaps  232  allow wires to pass through. The wire ends of the primary winding  7  are connected to the terminals  242 . 
     The second bobbin  4  is provided with a penetrating second through-hole  41 , which envelops the second side posts  12  on the same side of the two cores  1  at their outer peripheries. The second bobbin  4  is provided with a spacer  42  on the mid-section of the outer periphery of the second through-hole  41 . Winding regions  43  and  431  are formed on the two sides of the spacer  42 , respectively. 
     The bobbin mount  3  is disposed at the external flank of the second bobbin  4 . The bobbin mount  3  includes a base  31 . A barrier plate  34  is provided on a side of the base  31  closer to the first bobbin  2 . The barrier plate  34  is used for separating the first and second bobbins  2  and  4 . A second engaging slot  33  (e.g. a dovetail slot) and a second engaging tenon  331  (e.g. a dovetail tenon), corresponding to the first engaging tenon  251  and the first engaging slot  25 , respectively, are provided on a side of the bobbin mount  3  closer to the first bobbin  2 . By inserting the first engaging tenon  251  into the second engaging slot  33 , and the second engaging tenon  331  into the first engaging slot  25 , the bobbin mount  3  and the first bobbin  2  can be joined together. 
     A second side retainer  32  is provided on both ends of the side of the base  31  away from the barrier plate  34 . A plurality of terminals  322  are provided on each second side retainer  32 . The base  31  is provided with a middle slot  311  between the barrier plate  34  and the second side retainers  32 . A side slot  312  and a side slot  313  are provided on the two sides of the middle slot  311 . A second positioning recess  321  is provided on the side of each second side retainer  32  facing the barrier plate  34 . In one possible embodiment, the second positioning recess  321  has an edge shape conforming to the side of the core  1  closer to the second side post  12 , such that the second positioning recess  321  conforms to and abuts against the side edge of the core  1  closer to the second side post  12  to facilitate positioning. 
     Two metal plates  6  and  60  are bent to envelop the outer peripheries of the winding regions  43  and  431  of the second bobbin  4 , thereby forming a secondary winding. The metal plates  6  and  60  include lateral ends  61  and  601 , respectively, and middle ends  62  and  602 , respectively. The two metal plates  6  and  60  envelop the outer peripheries of the winding regions  43  and  431  of the second bobbin  4  in the opposite directions, such that the middle ends  62  and  602  of the metal plates  6  and  60  both pass through the middle slot  311 ; the lateral end  61  of the metal plate  6  passes through the lateral slot  312 ; and the lateral end  601  of the metal plate  60  passes through the lateral slot  313 . 
     In one possible embodiment, the lateral ends  61  and  601  extend downwards from lateral edges of the metal plates  6  and  60 , respectively, while the middle ends  62  and  602  bend and extend at the bottom middle portions of the metal plates  6  and  60 . As a result, the distances between the middle ends  62  and  602  (the middle slots  311 ) and the two lateral ends  61  and  601  (the two lateral slots  312 ) can be reduced. 
     The separating cover  5  is a “U-shape” insulating plate provided on the side of the first bobbin  2  closer to the bobbin mount  3 . The two ends of the separating cover  5  cover the top and bottom sides of the first bobbin  2 . A lateral flap  51  corresponding to each lateral fastening groove  221  is provided on each lateral edge of the separating cover  5 . By inserting each lateral flap  51  into the corresponding lateral fastening groove  221 , the separating cover  5  can be secured at the outer side of the coil slots  231  of the first bobbin  2 . 
     With the above structure and design, the present invention achieves at least the following technical effects: 
     1. Using the metal plates  6  and  60  in place of ordinary wires as the secondary winding, the overall current output capability is raised, and the size of the secondary winding (transformer) is effectively reduced. 
     2. By fitting the metal plates  6  and  60  onto the two winding regions  43  and  431  of the second bobbin  4 , assembly is easier than the traditional coil winding method, and processing efficiency is greatly increased. 
     3. By disposing the primary winding  7  and the metal plates  6  and  60  (secondary winding) on the first and second bobbins  2  and  4 , respectively, manufacturing of them can be performed in parallel simultaneously, and then the two are fastened together using corresponding engaging slots and tenons, and further assembled with other parts to form a complete transformer structure. This increases production speed and efficiency, while maintaining stable electrical characteristics of the transformer. 
     4. With the separating cover fencing off the primary and secondary, as well as the primary and the cores, the insulation strength and the creepage distance are increased, thus satisfying the more strict safety requirements specified in medical fields and the like. 
     In view of this, the resonant high current density transformer of present invention reduces the size of the transformer, increases power density and simplifies assembly process, and is thus submitted to be novel and non-obvious and a patent application is hereby filed in accordance with the patent law. It should be noted that the descriptions given above are merely descriptions of preferred embodiments of the present invention, various changes, modifications, variations or equivalents can be made to the invention without departing from the scope or spirit of the invention. It is intended that all such changes, modifications and variations fall within the scope of the following appended claims and their equivalents.