Abstract:
A transformer for reducing the electromagnetic interference (EMI) effect is disclosed. The transformer includes a bobbin; a magnetic core assembly partially sleeved by the bobbin; a first primary winding coiled around the bobbin; a secondary winding coiled on the first primary winding; and a first shielded element disposed between the first primary winding and the secondary winding for disconnecting the EMI transmission from the first primary winding to the secondary winding. The first primary winding includes a first winding portion and a second winding portion, and the first winding portion has larger EMI comparing to the second winding portion. The first winding portion of the first primary winding is adjacently disposed to the magnetic core assembly for shielding the EMI of the first primary winding by using the magnetic core assembly. The second winding portion is coiled on the first winding portion and adjacently disposed to the secondary winding for increasing the electromagnetic coupling rate of the first primary winding and the secondary winding. In addition, a power transform circuit applied in the transformer for reducing the EMI effect is also disclosed. The power transform circuit includes a switch, a power input for receiving a power signal; and a transformer electrically connected to the power input and the switch, for receiving and transforming the power signal.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a transformer, and more particularly to a transformer for reducing electromagnetic interference (EMI). The present invention relates to a power transform circuit, and more particularly to a power transform circuit applied in a transformer for reducing EMI. 
       BACKGROUND OF THE INVENTION 
       [0002]    Transformer is an electronic component for usually applying to various electronic apparatuses. Please refer to  FIG. 1  which is a structure diagram illustrating a conventional transformer. As shown in  FIG. 1 , a conventional transformer  1  includes a magnetic core assembly  11 , a bobbin  12 , a primary winding  13  and a secondary winding (not shown in  FIG. 1 ). The primary winding  13  and the secondary winding are coiled a winding region of the bobbin  12  by the sandwich-coiled type. That is, the primary winding  13  is separated to two portions covering the secondary winding, and the side-by-side adjacent region between the primary winding and the secondary winding are insulated by tape. Generally, the magnetic core assembly  11  is EE-core, EI-core or ER-core. The axle center  111  is disposed inside a channel  121  of the bobbin  12 , for resulting in the magnetic core assembly  11  with the primary winding  13  and the secondary winding to generate the electromagnetic coupling induction for achieving the purpose of voltage transform. 
         [0003]    Although the conventional transformer  1  certainly can achieve the effectiveness of voltage transform, there is still a problem need to be solved. When the transformer  1  is applied to a power transform circuit (not shown in  FIG. 1 ), the primary winding  13  of the transformer  1  is electrically connected to a switch of the power transform circuit, and the current passing through the primary winding  13  is connected or broken off by controlling the switch. However, when the switch is repeatedly OFF and ON, the current passed through the primary winding  13  is changed largely. Thus, the electromagnetic interference (EMI) is generated. While the primary winding  13  is closer the switch, the EMI is the more significant. Furthermore, the generation of EMI will affect the electromagnetic coupling rate of the primary winding  13  and secondary winding and increase the leakage inductance of the transformer  1 , resulting in lowering the operation efficiency of the transformer  1 . 
         [0004]    Therefore, the purpose of the present invention is to develop a transformer and a power transform circuit for reducing the effect of electromagnetic interference to deal with the above situations encountered in the prior art. 
       SUMMARY OF THE INVENTION 
       [0005]    An object of the present invention is to provide a transformer for reducing the EMI effect. 
         [0006]    Another object of the present invention is to provide a transformer for enhancing the electromagnetic coupling rate between primary windings and secondary windings, and increasing the transform efficiency. 
         [0007]    An additional object of the present invention is to provide a power transform circuit applied in a transformer for reducing the EMI effect. 
         [0008]    An additional object of the present invention is to provide a power transform circuit applied in a transformer for enhancing the electromagnetic coupling rate between primary windings and secondary windings, and increasing the transform efficiency of the transformer. 
         [0009]    According to an aspect of the present invention, there is provided a transformer. The transformer includes a bobbin; a magnetic core assembly partially sleeved by the bobbin; a first primary winding coiled around the bobbin; a secondary winding coiled on the first primary winding; and a first shielded element disposed between the first primary winding and the secondary winding for disconnecting the EMI transmission from the first primary winding to the secondary winding. The first primary winding includes a first winding portion and a second winding portion, and the first winding portion has larger EMI comparing to the second winding portion. The first winding portion of the first primary winding is adjacently disposed to the magnetic core assembly for shielding the EMI of the first primary winding by using the magnetic core assembly. The second winding portion is coiled on the first winding portion and adjacently disposed to the secondary winding for increasing the electromagnetic coupling rate of the first primary winding and the secondary winding. 
         [0010]    Preferably, the transformer further includes a second primary winding coiled on the secondary winding. The secondary primary winding includes a third winding portion and a fourth winding portion. Preferably, the first and second primary windings and the secondary winding are coiled by the sandwich-coiled type to make the secondary winding be coiled between the first and second primary windings. Preferably, the transformer further includes a second shielded element disposed between the second primary winding and the secondary winding, for preventing EMI of the second primary winding from transmitting to the secondary winding. Preferably, the first and second shielded elements are metal slices. Preferably, the EMI of the third winding portion is smaller than that of the fourth winding portion, the third winding portion coiled on the second shielded element is adjacently disposed to the secondary winding, and the fourth winding portion is coiled on the third winding portion, for increasing the electromagnetic coupling rate between the second primary winding and the secondary winding. Preferably, insulating materials are disposed between the first primary winding and the first shielded element, the secondary winding and the first shielded element, the secondary winding and the second shielded element, and the second primary winding and the second shielded element, respectively, to separate each other. Preferably, the insulating material is an insulating tape. 
         [0011]    According to another aspect of the present invention, there is provided a power transform circuit. The power transform circuit includes a switch; a power input for receiving a power signal; and a transformer electrically connected to the power input and the switch, for receiving and transforming the power signal. The transformer includes a bobbin; a magnetic core assembly partially sleeved by the bobbin; a first primary winding coiled around the bobbin; a secondary winding coiled on the first primary winding; and a first shielded element disposed between the first primary winding and the secondary winding for disconnecting the EMI transmission from the first primary winding to the secondary winding. The first primary winding includes a first winding portion and a second winding portion. The first winding portion is electrically connected to the switch and has EMI larger than that of the second winding portion. The first winding portion of the first primary winding is adjacently disposed to the magnetic core assembly for shielding the EMI of the first primary winding by using the magnetic core assembly. The second winding portion is coiled on the first winding portion and adjacently disposed to the secondary winding for increasing the electromagnetic coupling rate of the first primary winding and the secondary winding. 
         [0012]    Preferably, the transformer further includes a second primary winding coiled on the secondary winding. The second primary includes a third winding portion and a fourth winding portion. The third winding portion and the fourth winding portion are electrically connected to the power input and the first primary winding, respectively, and the EMI of the third winding portion is smaller than that of fourth winding portion. Preferably, the transformer further includes a second shielded element disposed between the second primary winding and the secondary winding, for disconnecting the EMI transmission from the second primary winding to the secondary winding. Preferably, the third winding portion of the second primary winding coiled on the second shielded element is adjacently disposed to the secondary winding. The fourth winding portion is coiled on the third winding portion, for increasing the electromagnetic coupling rate between the second primary winding and the secondary winding. Preferably, the power transform circuit further includes a jumper route electrically connected to the first and second shielded elements, and the switch, for forming a circuit having a minimum route among the first and second primary windings, the first and second shielded elements, and the switch to result in that the EMI of the first and second primary windings transmitting is limited among the minimum-route circuit, whereby reducing the EMI dispersion. 
         [0013]    Preferably, the switch is an N-channel metal-oxide-semiconductor (NMOS) field-effect transistor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The present invention may best be understood through the following description with reference to the accompanying drawings, in which: 
           [0015]      FIG. 1  is a structure diagram illustrating a conventional transformer; 
           [0016]      FIG. 2  is a circuit diagram illustrating a preferred embodiment of a power transform circuit according to the present invention; and 
           [0017]      FIG. 3  is a sectional diagram illustrating an axle center of the transformer from the most exterior winding layer to the magnetic core assembly of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]    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. 
         [0019]      FIG. 2  is a circuit diagram illustrating a preferred embodiment of a power transform circuit according to the present invention. As shown in  FIG. 2 , a power transform circuit  2  includes a power input V IN , a switch  21 , and a transformer  22 . The transformer  22  is electrically connected to the power input V IN  and the switch  21 , respectively. The transformer  22  includes a primary winding, a secondary winding, a first shielded element  221 , a second shielded element  222  and a plural of pins P 1 ˜P 4 , P 6 ˜P 11  and P 13 ˜P 14 . 
         [0020]    In the preferred embodiment of  FIG. 2 , the primary winding can include a first primary winding  23  and a second primary winding  24 , but not be limited to. The first primary winding  23  is respectively connected to the pins P 4  and P 3  of the transformer  22 , while the second winding  24  is respectively connected to the pins P 2  and P 3  of transformer  22 . Hence, the second primary winding  24  is electrically connected to the first winding  23  by the pin P 3 . Moreover, the secondary winding can include a plural of secondary windings  25 ˜ 29 , but not be limited to. As shown in FIG.  2 ., the secondary windings  25 ˜ 29  are in order connected to the pins P 14  and P 11 , the pins P 11  and P 13 , the pins P 13  and P 10 , the pins P 10  and P 8 , and the pins P 10  and P 9 , respectively. Therefore, the electromagnetic coupling induction is generated among the first and second primary windings  23  and  24 , and plural secondary windings  25 ˜ 29  by a magnetic core assembly  224  (as shown in  FIG. 3 ). 
         [0021]    In the preferred embodiment, the circle number of the first primary winding  23  can be, for example, 26 circles, and the circle number of the second primary winding  24  is also 26 circles. In addition, the number of circle of plural secondary windings  25 ˜ 29  can be, for example, 8, 4, 2, 8, and 6 circles, so the plural secondary windings  25 ˜ 28  can generate −5V, 3.3V, 5V and 12V to output, respectively. However, the circle number of first and second primary windings  23  and  24 , and plural secondary windings  25 ˜ 29 , and voltage output of the plural secondary windings  25 ˜ 28  are not limited to the above description. It can be altered according to the real voltage request of the transformer  22 . 
         [0022]    In this preferred embodiment, the first shielded element  221  and second shielded element  222  are respectively disposed between first and second primary windings  23  and  24  and plural secondary windings  25 ˜ 29  as shown in  FIG. 2 . On the other hand, in some preferred embodiments, the first and second shielded elements  221  and  222  can be, but not limited to, connected to the pin P 6  of the transformer  22  to connect the ground G 1 . 
         [0023]    As shown in  FIG. 2 , the transformer  22  can further includes a first auxiliary winding  200  and a second auxiliary winding  201 . The first auxiliary winding  200  is connected to the pins P 6  and P 7 , and electrically connected to the first and second shielded elements  221  and  222  by the pin P 6 . The first auxiliary winding  200  is used for providing the required power of a pulse width modulation (PWM) controller (not shown in  FIG. 2 ) to control the switch  21 . The second auxiliary winding  201  is connected to the pins P 1  and P 2  of the transformer  22 , and electrically connected to the first primary winding  23  by the pin P 2 . The second auxiliary winding  201  is used for providing additional power to the internal elements of the power transform circuit  2 . 
         [0024]    As shown in  FIG. 2 , the power input V IN  is connected to the pin P 2  of the transformer  22  to electrically connect to the second primary winding  24  and the second auxiliary winding  201 . Furthermore, the power input V IN  is electrically connected to the switch  21  through a capacitance C 1  and a resistance R 1 . The power input V IN  is used for receiving a power signal and providing the power signal to the first and second primary windings  23  and  24  and the first auxiliary winding  200  of the transformer  22 . 
         [0025]    The switch  21  is electrically connected to the power input V IN  and the transformer  22 , and can be an N-channel metal-oxide-semiconductor (NMOS) field-effect transistor but not be limited to. As shown in  FIG. 2 , the switch  21  includes a control terminal  211 , a first current transmitting terminal  212  and a second current transmitting terminal  213 . The control terminal  211  is used for receiving the control signal from the pulse width modulation (PWM) controller to control conduction or disconnection between the first current transmitting terminal  212  and the second current transmitting terminal  213 . The first current transmitting terminal  212  is connected to the pin P 4  of the transformer  22  to electrically connect to the first primary winding  23 , while the second current transmitting terminal  213  is connected to the ground G 2  by a resistance R 1 . Therefore, when the power input V IN  of the power transform circuit  2  receives a power signal, the power transform circuit  2  can control the current to pass through the first and second primary windings  23  and  24  by controlling the switch  21  to turn ON or OFF, resulting in the induction of the plural secondary windings  25 ˜ 29  of the transformer  22  to generate various voltage outputs. 
         [0026]      FIG. 3  is a sectional diagram illustrating an axle center of the transformer from the most exterior winding layer to the magnetic core assembly of  FIG. 2 . Please refer to  FIG. 2  and  FIG. 3  at same time. In this preferred embodiment, the 3-D structure appearance of the transformer  22  is similar to that of the conventional transformer  1  of  FIG. 1 . In other words, the transformer  22  is divided into two regions, the first and second regions, by using the axis of the magnetic core assembly as an axle. The first region includes from the most outer winding of the transformer  22  to the axis  2241  of the magnetic core assembly  224 , while the second region, corresponding to the first region, includes from the axis  2241  of the magnetic core assembly  224  to other the most outer winding of the transformer  22 . Since the first region and second region displays a mirror image symmetry by using the axis  2241  of the magnetic core assembly  224  as an axle, the detail structure of the transformer  22  of the preferred embodiment according to the present invention in  FIG. 3  is described by using the first region only. In addition, in order to easier understand the present invention, the pins&#39; labels correspondingly connecting to the two ends of the first primary winding  23 , the second primary winding  24 , the first auxiliary winding  200 , the second auxiliary winding  201  and plural secondary windings  25 ˜ 29  are directly indicated in  FIG. 3 . 
         [0027]    Please refer to  FIG. 3  and  FIG. 2 . The transformer  22  includes a first primary winding  23 , a second primary winding  24 , and a plural of secondary windings  25 ˜ 29 , a first shielded element  221 , a second shielded element  222 , a bobbin  223  and a magnetic core assembly  224 . In this embodiment, the 3-D structures of the bobbin  223  and the magnetic core assembly  224  are similar to those of the conventional bobbin  12  and magnetic core assembly  11  in  FIG. 1 . The bobbin  223  is used for the first primary winding  23 , the second primary winding  24 , and the plural secondary windings  25 ˜ 29  to coil thereon. Furthermore, the coiling way can be the sandwich-coiled type, but it is not limited to. That is, the plural secondary windings  25 ˜ 29  are wrapped between the first primary winding  23  and the second primary winding  24  as shown in  FIG. 3 . The axis  2241  of the magnetic core assembly  224  is partially disposed into the channel (not shown in  FIG. 3 ) of the bobbin  223  to position in the center of bobbin  223 , to make the first primary winding  23 , the second primary winding  24 , and the plural secondary windings  25 ˜ 29  generate electromagnetic coupling induction for achieving the purpose of the voltage transform of the transformer  22 . 
         [0028]    In this embodiment, the first primary winding  23  is coiled on the bobbin  223  and includes a first winding portion  231  and a second winding portion  232 . The end  231   a  of the first winding portion  231  is connected to the pin P 4  of the transformer  22  to electrically connect to the first current transmitting terminal  212  of the switch  21 . The second winding portion  232  is coiled on the first winding portion  231  and has the end  232   a  to connect to the pin P 3  of the transformer  22 . 
         [0029]    In this embodiment, the first shielded element  221  can be a metal slice, but not be limited to, and is coiled on the first primary winding  23 . As shown in  FIG. 3 , an insulating material  30 , such as insulating tape, is disposed between the first shielded element  221  and the first primary winding  23 , for achieving the effect to separate the first shielded element  221  and the first primary winding  23 . 
         [0030]    Please refer to  FIG. 3 . The secondary windings  26  and  27  are respectively coiled on the first shielded element  221 , and the other secondary windings  25 ,  28 , and  29  are coiled on the secondary windings  26  and  27 . The second shielded element  222  is disposed on the plural secondary windings  25 ˜ 29 , and can be a metal slice but not be limited to. In some embodiments, the insulating materials  30  are disposed between the secondary windings  25 ˜ 29  and the first shield element  221 , and the secondary windings  25 ˜ 29  and the second shielded element  222 , respectively, to separate each other. In addition, the insulating material  30  is also disposed between the secondary windings  25 ,  28  and  29  and the secondary winding  27  to achieve the separation effect. 
         [0031]    In this embodiment, the secondary winding  24 , including a third winding portion  241  and a fourth winding portion  242 , is coiled on the second shielded element  222 . The end  241   a  of the third winding portion  241  is connected to the pin P 2  to electrically connect to the power input V IN  of the power transform circuit  2 . Furthermore, the third wining portion  241  is adjacently disposed to the second shielded  222  and near the plural secondary windings  25 ˜ 29 . The fourth winding portion  242  is coiled on the third winding portion  241  and electrically connected to the first primary winding  23  by connecting the end  242   a  thereof to the pin P 3  of transformer  22 . Certainly, in another embodiment, the insulating material can be disposed between the second primary winding  24  and the second shielded element  222  to separate each other. 
         [0032]    As shown in  FIG. 3 , the first auxiliary winding  200  and the second auxiliary winding  201  are coiled on the second primary wining  24  and disposed the most outer layer of the transformer  22 . The insulating materials  30  are respectively disposed on the two sides of the first and second auxiliary windings  200  and  201 . That is, the first and second auxiliary windings  200  and  201  and the second primary winding  24  can be separated by the insulating material  30 . Since the first and second auxiliary windings  200  and  201  are disposed on the most outer layer of the bobbin  223  of the transformer  22  to wrap up the first and second primary windings  23  and  24 , the plural secondary windings  25 ˜ 29 , and the first and second shielded elements  221  and  222 , the electromagnetic coupling rate can be enhanced between the first and second primary windings  23  and  24  and the plural secondary windings  25 ˜ 29  besides the structure of the transformer  22  is tighter. 
         [0033]    Please refer  FIGS. 2 and 3 . When the switch  21  of the power transform circuit  2  is repeatedly switched by the control signal received by the control terminal  211 , the huge EMI is generated at the first primary winding  23  and the second primary winding  24 . Furthermore, the end  231   a  of the first winding portion  231  of the first primary winding  23  is electrically connected to the first current transmitting terminal  212  of the switch  21  directly, so the EMI of the first winding portion  231  is relatively greater than that of the second winding portion  232 . However, since the first winding portion  231  is directly coiled on the bobbin  223  and disposed at the most internal layer of the transformer  22  near the magnetic core assembly  224 , the EMI generated at the first winding portion  231  of the transformer  22  can be shielded by the axis  2241  of the magnetic core assembly  224 , for reducing the EMI effect on the internal elements of the transformer  22 . In addition, the second winding portion  232  having smaller EMI is coiled on the first winding portion  231  and adjacent to the plural secondary windings  25 ˜ 29 , so the electromagnetic coupling rate can be enhanced between the first primary winding  23  and the plural secondary windings  25 ˜ 29 . 
         [0034]    Moreover, the end  241   a  of the third winding portion  241  of the second primary winding  24  is electrically connected to the power input V IN  of the power transform circuit  2 , for receiving the power signal transmitted by the power input V IN . In comparison with the third winding portion  241 , the fourth winding portion  242  is more close to the first current transmitting terminal  212  of the switch  21 . Therefore, the EMI of the third winding portion  241  is smaller than that of the fourth winding portion  242 . Since the third winding portion  241  is disposed on the second shielded element  222  and adjacent to the plural secondary windings  25 ˜ 29  while the fourth winding portion  242  is coiled on the third winding portion  241  and far away from the plural secondary windings  25 ˜ 29 , the electromagnetic coupling rate can be enhanced between the second primary winding  24  and the plural secondary windings  25 ˜ 29 . 
         [0035]    In addition, the first and second shielded elements  221  and  222  have the effect to reduce the EMI affecting the transformer  22 . As shown in  FIG. 3 , since the first and second shielded elements  221  and  222  are disposed between the first primary winding  23  and the plural secondary windings  25 ˜ 29 , and the second winding  24  and the plural secondary windings  25 ˜ 29 , respectively, the EMI of the first and second primary windings  23  and  24  are respectively transmitted to the first and second shielded elements  221  and  222 . Furthermore, the first and second shielded elements  221  and  222  are connected to the ground G 1 , so the EMI is transmitted out by the ground G 1 . Therefore, the EMI of the first and second primary windings  23  and  24  can be separated and prevented from transmitting to the plural secondary windings  25 ˜ 29 , resulting in the electromagnetic coupling rates between the first and second primary windings  23  and  24  and the plural secondary windings  25 ˜ 29  are increased for enhancing the transform effect of the transformer  22 . 
         [0036]    Please refer to  FIG. 2 . The power transform circuit  2  further includes a jumper route J 1  having one end to connect to the first and second shielded elements  221  and  222  and the other end to electrically connect to the switch  21  through the resistance R 1 . The jumper route J 1  is used for forming the shortest circuit among the first and second shielded elements  221  and  222 , the switch  21  and the first and second primary windings  23  and  24 , resulting in the EMI generated from the first and second primary windings  23  and  24  can be transmitted in the shortest circuit repeatedly. Therefore, the EMI is unable to disperse to other routes of the power transform circuit  2 , so the transform effect of the transformer  22  can be enhanced. 
         [0037]    To sum up, the transformer and the power transform circuit applied thereto according to the present invention includes the first winding portion of the first primary winding having the largest EMI adjacently disposed to the magnetic core assembly, the second winding portion thereof and the third winding portion of the second primary winding having smaller EMI respectively and adjacently disposed to the plural secondary windings, and the first and second shielded elements respectively disposed between the first primary winding and the plural secondary windings, and the second primary winding and the plural secondary windings, for reducing the EMI effect on the transformer. Furthermore, the electromagnetic coupling rates between the first and second primary windings and the plural secondary windings can be increased, so the leakage inductance of the transformer can be reduced for enhancing the transform effect. 
         [0038]    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.