Patent Publication Number: US-7221252-B1

Title: Transformer

Description:
FIELD OF THE INVENTION 
   The present invention relates to a transformer, and more particularly to 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 magnetic core assembly  11  is generally shaped as an EE-type core, an EI-type core or an ER-type core. 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 for 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 separated 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  and a secondary winding coil  23 . The bobbin  21  comprises a first side plate  211 , a second side plate  212  and a winding member  213 . A 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 portion  2131  and a second winding portion  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 portion  2131  and the second winding portion  2132 , respectively. The first winding portion  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 portion  2131  and the first side plate  211 . Likewise, the second winding portion  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 portion  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 . 
   With increasing development of electronic technologies, the electric conversion efficiency of a power converter to be used in an electronic product is gradually demanding. For example, in a case that a voltage is intended to be converted from a low voltage (e.g. 400V) to a high voltage (e.g. 2,000V), for meeting the requirement of safety regulations, the distance between the primary winding coil and the secondary winding coil should be increased to avoid conduction between the primary winding coil and the secondary winding coil. Unfortunately, since the width d of the tape  24  is insufficient and the converted voltage is too high, the conduction between the primary winding coil and the secondary winding coil is possible. 
   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 
   An object of the present invention is to provide a transformer, which employs a partition plate to separate the primary winding coil and the secondary winding coil, or disposes the first winding portion and the second winding portion in the receptacles at different sides of the main body, respectively, to increase the distance between the primary winding coil and the secondary winding coil so as to increase the leakage inductance of the transformer. Moreover, the leakage inductance of the transformer can be adjusted through the distance between the protrusion of the U-shaped magnetic core and the I-shaped magnetic core, so as to enhance the electric safety and solve the defects of the prior art. 
   Another object of the present invention is to provide a transformer whose leakage inductance can be adjusted through the magnetic core assembly, so that it does not need to redevelop a new model for the bobbin, so as to reduce the manufacturing cost, time and labor. 
   According to an aspect of the present invention, there is provided a transformer structure. The transformer comprises a primary winding coil, plural secondary winding coils, a first winding portion, plural second winding portions, plural partition plates, a channel, and a magnetic core assembly. The first winding portion is used for winding the primary winding coil thereon, and the plural second winding portions are used for winding the secondary winding coils thereon and disposed at two sides of the first winding portion. The plural partition plates are disposed between the first winding portion and the second winding portions, respectively, and each the partition plate has a slot. The channel penetrates the first winding portion, the second winding portions and the partition plates. The magnetic core assembly comprises an I-shaped magnetic core and a U-shaped magnetic core. The I-shaped magnetic core is received in the channel and the U-shaped magnetic core has plural protrusions inserted into the slots of the partition plates. Thereby, a leakage inductance of the transformer is adjusted by a distance between the protrusions of the U-shaped magnetic core and the I-shaped magnetic core received in the channel. 
   In an embodiment, the slot of the partition plate has an opening on a top surface of the partition plate, and the protrusions of the U-shaped magnetic core are inserted into the slots from an upper side of the partition plates and disposed on the first winding portion and the second winding portions. 
   In an embodiment, the slot of the partition plate has an opening on a lateral side surface of the partition plate, and the protrusions of the U-shaped magnetic core are inserted into the slots from a lateral side of the partition plates and disposed at a side of the first winding portion and the second winding portions. 
   In an embodiment, the U-shaped magnetic core comprises two extensions disposed at two ends of the U-shaped magnetic core and contacting with two end parts of the I-shaped magnetic core. 
   In an embodiment, the protrusions are disposed between the extensions. 
   According to another aspect of the present invention, there is further provided a transformer structure. The transformer comprises a main body, a primary winding coil, plural secondary winding coils, a first winding portion, plural second winding portions and a magnetic core assembly. The main body comprises a first side, a second side, a first channel, a first receptacle communicating with the first side, plural second receptacles communicating with the second side, and plural openings. The second receptacles are disposed at two sides of the first receptacle, and a partition wall is disposed between the first receptacle and the second receptacles. The first winding portion is used for winding the primary winding coil thereon. The first winding portion is disposed in the first receptacle and has a second channel communicating with the first channel. The plural second winding portions are used for winding the secondary winding coils thereon and disposed in the second receptacles. Each the second winding portion has a third channel communicating with the first channel and a slot communicating with the opening of the main body. The magnetic core assembly comprises an I-shaped magnetic core and a U-shaped magnetic core. The I-shaped magnetic core is received in the first, second and third channels, and the U-shaped magnetic core has plural protrusions inserted into the slots of the second winding portions through the openings of the main body. Thereby, a leakage inductance of the transformer is adjusted by a distance between the protrusions of the U-shaped magnetic core and the I-shaped magnetic core received in the first, second and third channels. 
   In an embodiment, the first side is opposite to the second side. 
   In an embodiment, the U-shaped magnetic core comprises two extensions disposed at two ends of the U-shaped magnetic core. 
   In an embodiment, the protrusions are disposed between the extensions. 
   In an embodiment, the main body comprises plural indentations disposed at two sides of the main body and communicating with the first channel. 
   In an embodiment, two end parts of the I-shaped magnetic core are disposed in the indentations, and the extensions of the U-shaped magnetic core are disposed in the indentations and contacting with the two end parts of the I-shaped magnetic core. 
   In an embodiment, the main body further comprises plural blocks extending upwardly from a top surface of the main body for disposing the U-shaped magnetic core therebetween, and two ends of each the block extend to openings of the indentations. 
   The above objects and advantages 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; 
       FIG. 3(   a ) is a schematic diagram showing the disassembled structure of the transformer according to the first preferred embodiment of the present invention; 
       FIG. 3(   b ) is a schematic diagram showing the assembled structure of the transformer in  FIG. 3(   a ); 
       FIG. 4(   a ) is a schematic diagram showing the disassembled structure of the transformer according to the second preferred embodiment of the present invention; 
       FIG. 4(   b ) is a schematic diagram showing the assembled structure of the transformer in  FIG. 4(   a ); 
       FIG. 5(   a ) is a schematic diagram showing the disassembled structure of the transformer according to the third preferred embodiment of the present invention; 
       FIG. 5(   b ) is a cross-section through the A-A′ line in  FIG. 5(   a ); and 
       FIG. 5(   c ) is a schematic diagram showing the assembled structure of the transformer in  FIG. 5(   a ). 
   

   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. 
   Please refer to  FIG. 3(   a ), which is a schematic diagram showing the disassembled structure of the transformer according to the first preferred embodiment of the present invention. As shown in  FIG. 3(   a ), the transformer  3  comprises a primary winding coil  31 , plural secondary winding coils  32 , a first winding portion  33 , plural second winding portions  34 , plural partition plates  35 , a channel  36  and a magnetic core assembly  37 . The first winding portion  33  is used for winding the primary winding coil  31  thereon, and the plural second winding portions  34  are used for winding the plural secondary winding coils  31  thereon and disposed at the two sides of the first winding portion  33 . The partition plates  35  are disposed between the first winding portion  33  and the second winding portions  34 , respectively, and are used for separating the first winding portion  33  and the second winding portions  34 , so as to increase the distance between the primary winding coil  31  and the secondary winding coils  32 , and increase the leakage inductance of the transformer  3 . Each of the partition plates  35  has a slot  351 , and in this embodiment, the slot  351  has an opening disposed at the top surface of the partition plate  35 , but not limited thereto. 
   The channel  36  penetrates the first winding portion  33 , the second winding portions  34  and the partition plates  35 , and has openings at the outer sides of the second winding portions  34 , respectively, for disposing partial structure of the magnetic core assembly  37  therein. The magnetic core assembly  37  comprises an I-shaped magnetic core  371  and a U-shaped magnetic core  372 . The I-shaped magnetic core  371  can be inserted into the channel  36  from one of the openings at the two outer sides of the second winding portions  34 , and pass through the second winding portion  34 , the first winding portion  35  and the second winding portion  34  at the other end, and then penetrate out of the opening at the other outer side of the second winding portions  34 , so the middle part of the I-shaped magnetic core  371  is received in the channel  36  and the two end parts of the I-shaped magnetic core  371  are exposed outside the openings. The U-shaped magnetic core  372  comprises extensions  373  and protrusions  374 , wherein the extensions  373  are disposed at the two ends of the U-shaped magnetic core  372  and extend downwardly, and the protrusions  374  are disposed between the two extensions  373  and also extend downwardly. 
   When assembling the transformer  3 , the I-shaped magnetic core  371  is inserted in the channel  36 , the protrusions  374  of the U-shaped magnetic core  372  are inserted into the slots  351  of the partition plates  35  from the upper side so that the U-shaped magnetic core  372  is disposed on the first winding portion  33  and the second winding portions  34 , and the two extensions  373  of the U-shaped magnetic core  372  contact with the exposed end parts of the I-shaped magnetic core  371 , as shown in  FIG. 3(   b ). Thereby, an electromagnetic coupling effect is generated by the interaction of the magnetic core assembly  37 , the primary winding coil  31  and the secondary winding coils  32  for voltage regulation. 
   According to the present invention, the leakage inductance of the transformer  3  can be adjusted through the distance between the protrusion  374  of the U-shaped magnetic core  372  and the I-shaped magnetic core  371  received in the channel  36 . Therefore, the protrusion  374  can be designed in different length in accordance with different requirements for the leakage inductance of the transformer  3 , so it does not need to redesign the bobbin or the whole structure of the transformer for changing the leakage inductance, so as to reduce the design cost, time and labor. 
   Please refer to  FIG. 4(   a ), which is a schematic diagram showing the disassembled structure of the transformer according to the second preferred embodiment of the present invention. As shown in  FIG. 4(   a ), the transformer  4  comprises a primary winding coil  31 , plural secondary winding coils  32 , a first winding portion  33 , plural second winding portions  34 , plural partition plates  35 , a channel  36  and a magnetic core assembly  37 . Since the structures, positions and functions of the primary winding coil  31 , the plural secondary winding coils  32 , the first winding portion  33 , the plural second winding portions  34 , the plural partition plates  35 , the channel  36  and the magnetic core assembly  37  are the same as those of the first embodiment shown in  FIG. 3(   a ), they are not redundantly described here. 
   In this embodiment, the opening of the slot  351  is not disposed on the top surface of the partition plate  35 , but disposed at a lateral side surface of the partition plate  35 . When assembling the transformer  4 , the I-shaped magnetic core  371  is inserted in the channel  36 , the protrusions  374  of the U-shaped magnetic core  372  are inserted into the slots  351  from the lateral side and via the openings at the side surfaces of the partition plates  35  so that the U-shaped magnetic core  372  is disposed at the side of the first winding portion  33  and the second winding portions  34 , and the two extensions  373  of the U-shaped magnetic core  372  contact with the exposed end parts of the I-shaped magnetic core  371 , as shown in  FIG. 4(   b ). Thereby, an electromagnetic coupling effect is generated by the interaction of the magnetic core assembly  37 , the primary winding coil  31  and the secondary winding coils  32  for voltage regulation. 
   Please refer to  FIG. 5(   a ), which is a schematic diagram showing the disassembled structure of the transformer according to the third preferred embodiment of the present invention. As shown in  FIG. 5(   a ), the transformer  5  comprises a main body  51 , a primary winding coil  52 , plural secondary winding coils  53 , a first winding portion  54 , plural second winding portions  55 , and a magnetic core assembly  56 . 
   The main body  51  has a first side  511 , a second side  512 , a first receptacle  513 , plural second receptacles  514 , a first channel  515  and plural indentations  516 . The first side  511  is opposite to the second side  512 . The first receptacle  513  is located in the interior of the main body  51  and has an opening at the first side  511 . The two second receptacles  514  are located in the interior of the main body  51  and at the two sides of the first receptacle  513 , respectively, and each has an opening at the second side  512 . 
   The first winding portion  54 , which is used for winding the primary winding coil  52 , is disposed in the first receptacle  513 , and has a second channel  541 . The two second winding portions  55 , which are used for winding the secondary winding coils  53 , are disposed in the two second receptacles  514 , respectively, and each has a third channel  551  and a slot  552 . The first receptacle  513  and the second receptacles  514  are separated by a partition wall  517 . The main body  51  further comprises two openings  518  located at the top surface of the main body  51  and close to the partition wall  517 , and the two openings  518  communicate with the two second receptacles  514 , respectively. When the second winding portions  55  are disposed in the second receptacles  514 , the slots  552  of the second winding portions  55  will communicate with the openings  518  on the second receptacles  514 . 
   Since the first receptacle  513  and the second receptacles  514  have the partition wall disposed therebetween and have openings at opposite sides of the main body  51 , the creepage distance between the primary winding coil  54  and the secondary winding coils  55  can be lengthened due to the obstruction of the main body  51  when the first winding portion  54  and the second winding portions  55  are disposed in the first receptacle  513  and the second receptacles  514 , respectively, so as to enhance the electric safety and increase the leakage inductance. 
   The magnetic core assembly  56  comprises an I-shaped magnetic core  561  and a U-shaped magnetic core  562 . The U-shaped magnetic core  562  comprises extensions  563  and protrusions  564 , wherein the extensions  563  are disposed at the two ends of the U-shaped magnetic core  562  and extend downwardly, and the protrusions  564  are disposed between the two extensions  563  and also extend downwardly. The I-shaped magnetic core  561  can be inserted in the first channel  515  of the main body  51  and the second and third channels  541  and  551  of the first and second winding portions  54  and  55  when the first and second winding portions  54  and  55  are disposed in the first and second receptacles  513  and  514 , respectively, and the U-shaped magnetic core  562  can be disposed on the main body  51 . 
   Please refer to  FIG. 5(   b ), which is a cross-section through the A-A′ line in  FIG. 5(   a ). As shown in  FIG. 5(   b ), the indentations  516  disposed at the two sides of the main body  51  communicate with the openings of the first channel  515 , and the first channel  515  communicates with the first receptacle  513  and the second receptacles  514 . When the first and second winding portions  54  and  55  are disposed in the first and second receptacles  513  and  514 , respectively, the positions of the second and third channels  541  and  551  of the first and second winding portions  54  and  55  are corresponding to the first channel  515  of the main body  51 , that is to say, the first channel, the second channel and the third channels communicate with each other. 
   Please refer to  FIG. 5(   c ), which is a schematic diagram showing the assembled structure of the transformer in  FIG. 5(   a ). As shown in  FIG. 5(   c ), when assembling the transformer  5 , the first winding portion  54  with the primary winding coil  52  wound thereon and the second winding portions  55  with the secondary winding coils  53  wound thereon are inserted into the first receptacle  513  and the second receptacles  514 , respectively. Subsequently, the I-shaped magnetic core  561  is inserted into the main body  51  through the first channel  51 , the third channel  551  and the second channel  541 , and the end parts of the I-shaped magnetic core  561  are disposed in the indentations  516 . Then the U-shaped magnetic core  562  is assembled with the main body  51  from the upper side, wherein the protrusions  564  are inserted into the slots  552  of the second winding portions  55  through the openings  518  on the second receptacles  514 , and the two extensions  563  of the U-shaped magnetic core  562  are also disposed in the indentations  516  and contact with the exposed end parts of the I-shaped magnetic core  561 . Thereby, an electromagnetic coupling effect is generated by the interaction of the magnetic core assembly  56 , the primary winding coil  52  and the secondary winding coils  53  for voltage regulation. 
   In addition, the main body  51  further comprises two blocks  519  extending upwardly from the top surface of the main body  51 . The two ends of each of the blocks  519  extend to the openings of the indentations  516  for disposing the U-shaped magnetic core  562  therebetween when the main body  51  and the magnetic core assembly  56  are assembled. By means of the blocks  519  disposed on the man body  51 , the U-shaped magnetic core  562  can be secured on the main body  51  firmly, so as to enhance the structural stability of the transformer  5 . 
   In conclusion, the present invention employs the partition plate or the partition wall in the main body to separate the primary winding coil and the secondary winding coil and increase the distance between the primary winding coil and the secondary winding coil, so that the leakage inductance of the transformer can be increased. Moreover, the leakage inductance of the transformer can be adjusted through the distance between the protrusions of the U-shaped magnetic core and the I-shaped magnetic core received in the channel. Therefore, the protrusion can be designed in different length in accordance with different requirements for the leakage inductance of the transformer, so it does not need to redesign the bobbin or the whole structure of the transformer for changing the leakage inductance, so as to reduce the design cost, time and labor. 
   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.