Patent Publication Number: US-7218199-B1

Title: Structure of transformer

Description:
FIELD OF THE INVENTION 
   The present invention relates to a structure of a transformer, and more particularly to a structure of a transformer having increased leakage inductance. 
   BACKGROUND OF THE INVENTION 
   A transformer has become an essential electronic component for various kinds of electric appliance. Referring to  FIG. 1 , a schematic exploded view of a conventional transformer is illustrated. The transformer  1  principally comprises a magnetic core assembly  11 , a bobbin  12 , a primary winding coil  13  and a secondary winding coil  14 . The primary winding coil  13  and the secondary winding coil  14  are wounded around the bobbin  12 . A tape  15  is provided for isolation and insulation. The middle portions  111  of the core  11  are embedded into the cylinder tube  121  of the bobbin  12 . The primary winding coil  13  and the secondary winding coil  14  interact with the magnetic core assembly  11  to achieve the purpose of voltage regulation. 
   Since the leakage inductance of the transformer has an influence on the electric conversion efficiency of a power converter, it is very important to control leakage inductance. Related technologies were developed to increase coupling coefficient and reduce leakage inductance of the transformer so as to reduce power loss upon voltage regulation. In the transformer of  FIG. 1 , the primary winding coil  13  and the secondary winding coil  14  are superimposed with each other and wounded around the bobbin  12 . As a consequence, there is less magnetic flux leakage generated from the primary winding coil  13  and the secondary winding coil  14 . Under this circumstance, sine the coupling coefficient is increased, the leakage inductance of the transformer is reduced and the power loss upon voltage regulation is reduced, the electric conversion efficiency of a power converter is enhanced. 
   In the power supply system of the electric products in the new generation, for example LCD televisions, the transformer with leakage inductance prevails. The current generated from the power supply system will pass through a LC resonant circuit composed of an inductor L and a capacitor C. The inductor L is provided from the primary winding coil of the transformer. Meanwhile, the current with a near half-sine waveform will pass through a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) switch. When the current is zero, the power MOSFET switch is conducted. After a half-sine wave is past and the current returns zero, the switch is shut off. As known, this soft switch of the resonant circuit may reduce damage possibility of the switch and minimize the noise. 
   In order to increase the leakage inductance of the transformer, the primary winding coil should be separate from the secondary winding coil by a certain distance to reduce the coupling coefficient of the transformer. Referring to  FIG. 2 , a schematic exploded view of a transformer with leakage inductance according to prior art is illustrated. The transformer  2  principally comprises a bobbin  21 , a primary winding coil  22 , a secondary winding coil  23  and a tape  24 . The bobbin  21  comprises a first side plate  211 , a second side plate  212  and a winding member  213 . The tape  24  is wound around the middle portion of the winding member  213  and has a width d. The winding member  213  is divided into a first winding section  2131  and a second winding section  2132 , which are located at bilateral sides of the tape  24 . The primary winding coil  22  and the secondary winding coil  23  are wound around the first winding section  2131  and the second winding section  2132 , respectively. The first winding section  2131  is separated from the first side plate  211  by wrapping a first side tape  25  on the winding member  213  between the first winding section  2131  and the first side plate  211 . Likewise, the second winding section  2132  is separated from the second side plate  212  by wrapping a second side tape  26  on the winding member  213  between the second winding section  2132  and the second side plate  212 . For safety regulations, the tape  24  is used for isolation between the primary winding coil  22  and the secondary winding coil  23 . Via the first side tape  25  and the second side tape  26 , the primary winding coil  22  and the secondary winding coil  23  are electrically isolated from the conductors outside the transformer  2 . As the width d of the tape  24  between the primary winding coil  22  and the secondary winding coil  23  is increased, the coupling coefficient is reduced and the leakage inductance of the transformer is increased. Under this circumstance, the resonant circuit of the power supply system will be conveniently controlled. 
   Although the transformer structure of  FIG. 2  is advantageous for increasing the leakage inductance, some drawbacks still exist. As previously described, the magnitude of the leakage inductance is dependent on the width d of the tape  24  between the primary winding coil  22  and the secondary winding coil  23 . Since the tape  24  is made of flexible material and fails to be firmly fixed, the structure of the transformer is readily distorted due to a long-term using period or serious vibration. Under this circumstance, the magnitude of the leakage inductance is reduced or unstable, and the resonant circuit of the power supply system will be adversely affected. Since these tapes are sticky and narrow in width, the procedures of wrapping the tape  24 , the first side tape  25  and the second side tape  26  are labor-intensive and complicated. In addition, if the wrapping result is unsatisfied, the electrical performance of the transformer is impaired. 
   Since the tape  24 , the first side tape  25  and the second side tape  26  are wrapped on the winding member  213  of the bobbin  21 , the remaining area or volume for winding the primary winding coil  22  and the secondary winding coil  23  around the winding member  213  is limited and thus the heat-dissipating effect is usually insufficient. Furthermore, after the procedures of winding the coils and wrapping the tapes, a layer of insulating tape is additionally wrapped around the primary winding coil  22  and the secondary winding coil  23 . The insulating tape also impairs heat dissipation of the transformer during operation. Moreover, since the melting point of the tape  24  is relatively lower, the operating temperature of the transformer is restricted by the melting point of the tape  24 . 
   Furthermore, since the secondary winding coil of the conventional transformer is manually wound and fabricated, the labor cost is increased and the fabricating efficiency is reduced. The diameter of the secondary winding coil is too small to be used in high power application. 
   In views of the above-described disadvantages, the applicant keeps on carving unflaggingly to develop a structure of a transformer according to the present invention through wholehearted experience and research. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a structure of a transformer for effectively controlling and increasing leakage inductance, and enhancing electric safety. 
   It is another object of the present invention to provide a transformer, which is simple in the structure, easily assembled and cost-effective. 
   In accordance with an aspect of the present invention, there is provided a transformer. The transformer comprises a primary winding coil, a plurality of electrically-conductive sheets, a bobbin and a magnetic core assembly. The bobbin comprises a first tube member, a second tube member and plural partition plates. The first tube member and the second tube member have a first channel and a second channel therein, respectively. Each partition plate is sheathed around the first tube member and the second tube member and includes a receptacle for accommodating respective electrically-conductive sheet, and the primary winding coil is wound around the second tube member. 
   In accordance with another aspect of the present invention, there is provided a transformer. The transformer comprises a primary winding coil, a plurality of electrically-conductive sheets, a main body, a primary winding coil frame and a magnetic core assembly. The main body comprises a first surface, plural apertures, a first tube member, plural partition plates and a first receptacle. The first receptacle is next to the first surface, the first tube member has a first channel therein, and each partition plate is sheathed around the first tube member and includes a second receptacle for accommodating respective electrically-conductive sheet. The primary winding coil frame is accommodated within the first receptacle and including a second tube member. The second tube member has a second channel therein and a winding section for winding the primary winding coil thereon, and the second channel of the second tube member is communicated with corresponding apertures of the main body. The magnetic core assembly is partially embedded into the first channel of the first tube member, the apertures of the main body and the second channel of the second tube member. 
   The above contents of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic exploded view of a conventional transformer; 
       FIG. 2  is a schematic exploded view of another conventional transformer with leakage inductance; 
       FIG. 3(   a ) is a schematic exploded view illustrating a transformer according to a first preferred embodiment of the present invention; 
       FIG. 3(   b ) is a cross-sectional view of  FIG. 3(   a ) taken along the line A–A′; 
       FIG. 3(   c ) is a schematic exploded view of the transformer according to the first preferred embodiment, in which the primary winding coil is wound around the second tube member; 
       FIG. 3(   d ) is a schematic assembled view of the transformer according to the first preferred embodiment; 
       FIG. 4(   a ) is a schematic exploded view illustrating a transformer according to a second preferred embodiment of the present invention; 
       FIG. 4(   b ) is a cross-sectional view of  FIG. 4(   a ) taken along the line B–B′; 
       FIG. 4(   c ) is a schematic exploded view of the transformer according to the second preferred embodiment, in which the primary winding coil is wound around the second tube member; 
       FIG. 4(   d ) is a schematic assembled view of the transformer according to the second preferred embodiment; 
       FIG. 5(   a ) is a schematic exploded view illustrating a transformer according to a third preferred embodiment of the present invention; 
       FIG. 5(   b ) is a schematic exploded view of the transformer according to the third preferred embodiment, in which the primary winding coil is wound around the second tube member; and 
       FIG. 5(   c ) is a schematic assembled view of the transformer according to the third preferred embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed. 
   Referring to  FIGS. 3(   a ) and  3 ( c ), schematic exploded views of a transformer according to a first preferred embodiment of the present invention is illustrated. The transformer  3  comprises a plurality of electrically-conductive sheets  31 , a magnetic core assembly  32 , a primary winding coil  33  (as shown in  FIG. 3(   c )) and a bobbin  34 . 
   The bobbin  34  comprises a first tube member  35 , a second tube member  36 , plural partition plates  37 , two side plates  38  and plural pins  39 . The first tube member  35  and the second tube member  36  are arranged between and connected to these two side plates  38 . The first tube member  35  and the second tube member  36  are substantially parallel with each other. Please also refer to  FIG. 3(   b ). The first tube member  35  and the second tube member  36  have a first channel  351  and a second channel  361  therein, respectively. 
   In this embodiment, the plural partition plates  37  are all sheathed around the first tube member  35  and the second tube member  36 . In addition, each partition plate  37  has a receptacle  371  corresponding to the first tube member  35  and is used for accommodating respective electrically-conductive sheet  31  therein, as is shown in  FIG. 3(   d ). As also shown in  FIG. 3(   b ), within the receptacle  371  of each partition plate  37 , the channel  351  of the first tube member  35  is covered by a side wall  352 . After the electrically-conductive sheet  31  is accommodated within the receptacle  371 , the electrically-conductive sheet  31  is separated from the magnetic core assembly  32 , which is embedded into the first channel  351 . 
   Please refer to  FIGS. 3(   a ) and  3 ( c ). Since the plural partition plates  37  are sheathed around the first tube member  35  and the second tube member  36 , a winding section  373  is defined between any two adjacent partition plates  37  for winding the primary winding coil  33  thereon. Furthermore, each partition plate  37  has a V-shaped notch  372  beside the second tube member  36 . For winding the primary winding coil  33  on the bobbin  34 , a terminal of the primary winding coil  33  is firstly soldered on a pin  39  under one of the side plates  38 . The primary winding coil  33  is successively wound around the winding sections  373  from this side plate  38  to the opposite side plate  38  through the V-shaped notches  372 . Afterward, the other terminal of the primary winding coil  33  is soldered onto the pin  39  on the opposite side plate  38 . 
   In addition, these two side plates  38  have several apertures  381  in communication with the first channel  351  of the first tube member  35  and the second channel  361  of the second tube member  36 . 
   The magnetic core assembly  32  of the transformer  3  includes a first magnetic part  321  and a second magnetic part  322 , which are cooperatively formed as a UU-type core assembly or a UI-type core assembly. Take the UU-type core assembly for example. Each of the first magnetic part  321  and the second magnetic part  322  is a U-shaped magnetic core with two extension parts  323 . The extension parts  323  of the first magnetic part  321  and the second magnetic part  322  are embedded into the first channel  351  of the first tube member  35  and the second channel  361  of the second tube member  36 . Furthermore, the extension parts  323  of the first magnetic part  321  are in contact with the extension parts  323  of the second magnetic part  322 . In the configuration as shown in  FIG. 3(   d ), the primary winding coil  33  and the electrically-conductive sheets  31  interact with the magnetic core assembly  32  to achieve the purpose of voltage regulation and output the DC voltage via the external wires (not shown) connected to the electrically-conductive sheets  31 . 
   In the above embodiment, the electrically-conductive sheets  31  are U-shaped and made of high conductive material such as copper. The electrically-conductive sheets  31  are accommodated within corresponding receptacles  371  of the partition plates  37  and stride over the side wall  352 . 
   In the above embodiment, the transformer  3  of the present invention utilizes the electrically-conductive sheets  31  in replace of the conventional secondary winding coil. After the primary winding coil  33  is wound around the second tube member  36  and the electrically-conductive sheets  31  and the magnetic core assembly  32  are mounted onto the bobbin  34 , the transformer  3  is finished in a simplified manner. Since the volume and the cross-section of the electrically-conductive sheet  31  are large, the output power of the transformer  3  is increased. As a consequence, the problem of causing low output power limited by the small diameter of the secondary winding coil in the prior art will be overcome. Furthermore, since the electrically-conductive sheets  31  are made of high conductive material and the partition plates  37  have receptacles  371 , the overall heat-dissipating efficiency of the transformer  3  is enhanced. 
   Referring to  FIG. 4(   a ), a schematic exploded view of a transformer according to a second preferred embodiment of the present invention is illustrated. The transformer  4  comprises a plurality of electrically-conductive sheets  41 , a magnetic core assembly  42 , a primary winding coil  43  (as shown in  FIG. 4(   c )), a primary winding coil frame  44  and a main body  45 . 
   The main body  45  comprises a first tube member  46 , plural partition plates  47 , a first surface  48 , a first receptacle  481  next to the first surface  48 , two side plates  49  and plural apertures  491 . The first tube member  46  is arranged between and connected to these two side plates  49 . The first tube member  46  has a first channel  461  therein, as is shown in  FIG. 4(   b ). 
   In this embodiment, the plural partition plates  47  are sheathed around the first tube member  46 . In addition, each partition plate  47  has a second receptacle  471  for accommodating respective electrically-conductive sheet  41  therein, as is shown in  FIG. 4(   d ). As also shown in  FIG. 4(   b ), within the second receptacle  471  of each partition plate  47 , the first channel  461  of the first tube member  46  is covered by a first side wall  462 . After the electrically-conductive sheets  41  are accommodated within the second receptacles  471 , the electrically-conductive sheets  41  are separated from the magnetic core assembly  42 , which is embedded into the first channel  461 . In addition, the first receptacle  481  also has a second side wall  482  adjacent to the first surface  48  and the second receptacle  471 . By the second side wall  482 , the primary winding coil  43  which is wound around the primary winding coil frame  44  is separated from the electrically-conductive sheets  41  accommodated within the second receptacles  471 . 
   In addition, these two side plates  49  of the main body  45  have several apertures  491  in communication with the first channel  461  of the first tube member  46  and the first receptacle  481 . 
   Please refer to  FIGS. 4(   a ) and  4 ( c ). The primary winding coil frame  44  is accommodated within the first receptacle  481  of the main body  45 , and comprises two side plates  441 , a second tube member  442  and several pins  446  under the side plates  441 . The second tube member  442  is arranged between and connected to these two side plates  441 . The second tube member  442  has a second channel  443  therein and a winding section  445  for winding the primary winding coil  43  thereon. Each side plate  441  has an aperture  444  in communication with the second channel  443  of the second tube member  442 . For winding the primary winding coil  43  on the second tube member  442  of the primary winding coil frame  44 , a terminal of the primary winding coil  43  is firstly soldered on a pin  446  under one of the side plates  441 . The primary winding coil  43  is successively wound around the winding section  445  from this side plate  441  to the opposite side plate  441 . Afterward, the other terminal of the primary winding coil  43  is soldered onto the pin  446  on the opposite side plate  441 . 
   The magnetic core assembly  42  of the transformer  4  includes a first magnetic part  421  and a second magnetic part  422 , which are cooperatively formed as a UU-type core assembly or a UI-type core assembly. Take the UU-type core assembly for example. Each of the first magnetic part  421  and the second magnetic part  422  is a U-shaped magnetic core with two extension parts  423 . The extension parts  423  of the first magnetic part  421  and the second magnetic part  422  are embedded into the first channel  461  of the first tube member  46 , the apertures  491  of the main body  45 , the apertures  444  of the primary winding coil frame  44  and the second channel  443  of the second tube member  442 . Furthermore, the extension parts  423  of the first magnetic part  421  are in contact with the extension parts  423  of the second magnetic part  422 . In the configuration as shown in  FIG. 4(   d ), the primary winding coil  43  and the electrically-conductive sheets  41  interact with the magnetic core assembly  42  to achieve the purpose of voltage regulation and output the DC voltage via the external wires (not shown) connected to the electrically-conductive sheets  41 . 
   In the above embodiment, the electrically-conductive sheets  41  are U-shaped and made of high conductive material such as copper. The electrically-conductive sheets  41  are accommodated within corresponding second receptacles  471  of the partition plates  47  and stride over the first side wall  452 . 
   Referring to  FIG. 5(   a ), a schematic exploded view of a transformer according to a third preferred embodiment of the present invention is illustrated. The transformer  4  also comprises a plurality of electrically-conductive sheets  41 , a magnetic core assembly  42 , a primary winding coil  43  (as shown in  FIG. 5(   b )), a primary winding coil frame  44  and a main body  45 . The electrically-conductive sheets  41 , the magnetic core assembly  42  and the main body  45  included therein are similar to those shown in  FIG. 4(   a ), and are not redundantly described herein. 
   In this embodiment, between the side plates  441 , the primary winding coil frame  44  further comprises plural partition plates  447 , which are sheathed around the second tube member  442 . As a consequence, a winding section  448  is defined between any two adjacent partition plates  447  for winding the primary winding coil  43  thereon. Furthermore, each partition plate  447  has a V-shaped notch  449 . Please refer to  FIG. 5(   b ), for winding the primary winding coil  43  on the second tube member  442  of the primary winding coil frame  44 , a terminal of the primary winding coil  43  is firstly soldered on a pin  446  under one of the side plates  441 . The primary winding coil  43  is successively wound around the winding sections  448  from this side plate  441  to the opposite side plate  441  through the V-shaped notches  449 . Afterward, the other terminal of the primary winding coil  43  is soldered onto the pin  446  on the opposite side plate  441 . 
   The process for assembling the transformer  4  is identical to that described in the second embodiment, and is not redundantly described herein. The assembled structure of the transformer  4  is illustrated with reference to  FIG. 5(   c ). 
   In the above embodiments, the transformer  4  of the present invention utilizes the electrically-conductive sheets  41  in replace of the conventional secondary winding coil. After the primary winding coil  43  is wound around the second tube member  442 , the primary winding coil frame  44  is accommodated within the first receptacle  481 , and the electrically-conductive sheets  41  and the magnetic core assembly  42  are mounted onto the main body  45 , the transformer  4  is finished in a simplified manner. Since the volume and the cross-section of the electrically-conductive sheet  41  are large, the output power of the transformer  4  is increased. As a consequence, the problem of causing low output power limited by the small diameter of the secondary winding coil in the prior art will be overcome. Furthermore, since the electrically-conductive sheets  41  are made of high conductive material and the partition plates  47  have second receptacles  471 , the overall heat-dissipating efficiency of the transformer  4  is enhanced. 
   From the above description, by using the electrically-conductive sheets to replace the conventional secondary winding coil, the process of fabricating the transformer is simplified, the electric conversion efficiency is enhanced and the heat-dissipating efficiency is increased. In addition, since the electrically-conductive sheets are accommodated within the receptacles of the partition plates and/or the primary winding coil frame is accommodated within the receptacle of the main body, the distance between the primary winding coil and the electrically-conductive sheets is increased, the coupling coefficient is reduced, the leakage inductance of the transformer is increased and the electric safety is enhanced. 
   While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.