Patent Publication Number: US-2023136361-A1

Title: Common mode filter

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a common mode filter and, more particularly, to a common mode filter of a type in which a pair of wires cross each other on the way and a manufacturing method therefor. 
     Description of Related Art 
     A common mode filter is widely used in many electronic devices, such as mobile electronic devices and on-vehicle LANs, as an element for removing common mode noise superimposed on differential signal lines. In recent years, a common mode filter using a surface-mountable drum core supersedes a common mode filter using a toroidal core (see JP 2014-199904 A). 
     In the common mode filter described in JP 2014-199904 A, a pair of wires are made to cross each other on the way to thereby enhance symmetry between differential signals in a high-frequency region. 
     However, when the pair of wires are made to cross each other on the way, the positional relationship between the wires is inverted, so that it is necessary to cross the wires once again in order to restore the positional relationship to its original state. Then, when the second crossing is made near the wire end portion, a difference occurs, in which the wires cross each other at one end portion while they do not cross each other at the other end portion, which may cause deterioration of high-frequency characteristics such as reflection characteristics (return loss) or noise conversion characteristics. 
     SUMMARY 
     It is therefore an object of the present invention to improve high-frequency characteristics in the common mode filter in which the pair of wires are made to cross each other. 
     A common mode filter according to the present invention includes a winding core part and first and second wires wound in the same direction around the winding core part. The first and second wires constitute a first winding block wound a plurality of turns on one endmost side in the axial direction of the winding core part and a second winding block wound a plurality of turns on the other endmost side in the axial direction of the winding core part, and a third winding block positioned between the first and second winding blocks and including an odd number of blocks each wound a plurality of turns. The second winding block is a winding block at an odd-numbered position counted from the first winding block. The first and second wires cross each other in an area between the first and third winding blocks and in an area between the second and third winding blocks. 
     According to the present invention, the number of the winding blocks is an odd number, so that when the first and second wires are made to cross each other even number of times in the areas between the winding blocks axially adjacent to each other, the positional relationship between the first and second wires at one end portion and that at the other end portion can be made to coincide with each other. As a result, conditions of one and the other end portions of the first and second wires coincide with each other, making it possible to enhance high-frequency characteristics such as reflection characteristics (return loss) or noise conversion characteristics. 
     In the present invention, the number of turns in the first winding block and that in the second winding block may be equal to each other. This enhances symmetry between the first and second winding blocks positioned on both sides, making it possible to eliminate product directionality. 
     In the present invention, the total number of turns in the first and second winding blocks and the number of turns in the third winding block may be equal to each other. Thus, when focusing on the same turns of the first and second wires, the number of pairs of the first and second wires in which the first wire is positioned on the one end side and the number of pairs of the first and second wires in which the second wire is positioned on the one end side coincide with each other. This enhances symmetry between signals flowing in the first and second wires, with the result that excellent high-frequency characteristics can be obtained. 
     In the present invention, the first, second, and third winding blocks may each have a first winding layer positioned in the lower layer and a second winding layer positioned on the upper layer of the first winding layer. This enhances wire winding density, making it possible to reduce the size of the winding core part in the axial direction. 
     In the present invention, the first and second wires may be positioned in the first winding layer and second winding layer, respectively, in any of the first, second, and third winding blocks. This allows the common mode filter to be produced by sequentially winding the first and second wires in this order. Alternatively, a configuration may be possible, in which the first and second wires are positioned in the first winding layer and second winding layer, respectively in the first and second winding blocks, and the first and second wires are positioned in the second winding layer and first winding layer, respectively in the third winding block. This can reduce a difference in length between the first and second wires. 
     In the present invention, the third winding block may include fourth, fifth, and sixth winding blocks arranged in this order as viewed from the first winding block. The first and second wires may cross each other in an area between the first and fourth winding blocks, in an area between the fourth and fifth winding blocks, in an area between the fifth and sixth winding blocks, and in an area between the sixth and second winding blocks. Thus, the first and second wires can be made to cross each other four times. 
     In the present invention, the number of turns in the first winding blocks and that in the fifth winding block may be equal to each other. This can enhance symmetry between the first and fifth winding blocks being at odd-numbered positions. 
     In the present invention, the number of turns in the fourth winding blocks and that in the sixth winding block may be equal to each other. This can enhance symmetry between the first and fifth winding blocks being at even-numbered positions. 
     In the present invention, the total number of turns in the first, second, and fifth winding blocks may be equal to that in the fourth and sixth winding blocks. This enhances symmetry between signals flowing in the first and second wires, making it possible to obtain excellent high-frequency characteristics. 
     In the present invention, the number of turns of each of odd-numbered winding blocks counting from the first winding block may be smaller than the number of turns of each of even-numbered winding blocks. This can reduce a difference between the total number of turns of the odd-numbered winding blocks and the total number of turns of the even-numbered winding blocks. 
     As described above, according to the present invention, it is possible to enhance the reflection characteristics of the common mode filter in which the pair of wires are made to cross each other on the way. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above features and advantages of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a schematic perspective view illustrating the outer appearance of a common mode filter according to a preferred embodiment of the present invention; 
         FIG.  2    is a schematic view for more specifically explaining the winding layout of the first and second wires; 
         FIG.  3    is a schematic view for explaining a reason why the 24th turns of the respective first and second wires do not cross each other; 
         FIG.  4    is a schematic view for explaining a state where the last turns of the respective first and second wires cross each other in a common mode filter of a comparative example; 
         FIG.  5    is a schematic view for explaining another state where the last turns of the respective first and second wires cross each other in a common mode filter of a comparative example; 
         FIG.  6    is a schematic view for explaining still another state where the last turns of the respective first and second wires cross each other in a common mode filter of a comparative example; 
         FIG.  7    is a schematic view for explaining the winding layout of a common mode filter according to a first modification; 
         FIG.  8    is a schematic view for explaining the winding layout of a common mode filter according to a second modification; and 
         FIG.  9    is a schematic view for explaining the winding layout of a common mode filter according to a third modification. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Preferred embodiments of the present invention will be explained below in detail with reference to the accompanying drawings. 
       FIG.  1    is a schematic perspective view illustrating the outer appearance of a common mode filter  10  according to a preferred embodiment of the present invention. 
     As illustrated in  FIG.  1   , the common mode filter  10  according to the present embodiment includes a drum core  20 , a plate core  30 , first to fourth terminal electrodes  41  to  44 , and first and second wires W 1  and W 2 . The drum core  20  and plate core  30  are each made of a magnetic material having comparatively high permeability, such as an Ni—Zn based ferrite. The first to fourth terminal electrodes  41  to  44  are each a metal fitting made of a good conductor material such as copper. The first to fourth terminal electrodes  41  to  44  may be obtained by directly baking silver paste or the like onto the drum core  20 . 
     The drum core  20  has a first flange part  21 , a second flange part  22 , and a winding core part  23  disposed between the first and second flange parts  21  and  22 . The winding core part  23  has its axial direction in the x-direction. The first and second flange parts  21  and  22  are disposed at both ends of the winding core part  23  in the axial direction and integrally formed with the winding core part  23 . The plate core  30  is bonded to upper surfaces  21   t  and  22   t  of the respective flange parts  21  and  22 . The upper surfaces  21   t  and  22   t  of the respective flange parts  21  and  22  constitute the xy plane, and their opposite surfaces are used as mounting surfaces  21   b  and  22   b.  The first and second terminal electrodes  41  and  42  are each provided on the mounting surface  21   b  and an outer surface  21   s  of the first flange part  21 , and the third and fourth terminal electrodes  43  and  44  are each provided on the mounting surface  22   b  and an outer surface  22   s  of the second flange part  22 . The outer surfaces  21   s  and  22   s  each constitute the yz plane. The first to fourth terminals  41  to  44  are fixed by using an adhesive or the like. 
     The first and second wires W 1  and W 2  are wound around the winding core part  23  in the same direction. One and the other ends of the first wire W 1  are connected respectively to the first and third terminal electrodes  41  and  43 , and one and the other ends of the second wire W 2  are connected respectively to the second and fourth terminal electrodes  42  and  44 . The numbers of turns of the first and second wires W 1  and W 2  are the same. 
     As illustrated in  FIG.  1   , the winding core part  23  of the drum core  20  includes a first winding area A 1  closest to the first flange part  21 , a second winding area A 2  closest to the second flange part  22 , and a third winding area A 3  positioned between the first and second winding areas A 1  and A 2 . The area between the first and third winding areas A 1  and A 3  constitutes a first crossing area CA 1 , and the area between the second and third winding areas A 2  and A 3  constitutes a second crossing area CA 2 . The first and second wires W 1  and W 2  are aligned and wound in the first to third winding areas A 1  to A 3  and cross each other in the first and second crossing areas CA 1  and CA 2 . When the first and second wires W 1  and W 2  cross each other, the positional relationship between the first and second wires W 1  and W 2  is changed before and after the crossing point. 
       FIG.  2    is a schematic view for explaining more in detail the winding layout of the first and second wires W 1  and W 2 . 
     As illustrated in  FIG.  2   , the first and second wires W 1  and W 2  constitute a first winding block B 1  wound around the first winding area A 1 , a second winding block B 2  wound around the second winding area A 2 , and a third winding block B 3  wound around the third winding area A 3 . As described above, the first and second wires W 1  and W 2  cross each other in the first and second crossing areas CA 1  and CA 2 . In the example of  FIG.  2   , the number of turns in the first winding block B 1  and that in the second winding block B 2  are each six, and the number of turns in the third winding block B 3  is 12. As a result, the first and second wires W 1  and W 2  each have a 24-turn configuration including 1st to 24th turns, but not limited thereto. 
     The first to third winding blocks B 1  to B 3  each have a double layer structure including a first winding layer S 1  positioned in the lower layer and directly wound around the winding core part  23  and a second winding layer S 2  positioned on the upper layer of the first winding layer S 1  and wound around the winding core part  23  through the first winding layer S 1 . The first wire W 1  is positioned in the first winding layer S 1 , and most part of the second wire W 2  is positioned in the second winding layer S 2 . However, the 6th, 8th, and 24th turns of the second wire W 2  are positioned in the first winding layer S 1 . This is because, in order to make the wires constituting the double layer structure stable, it is necessary to wound the upper layer wire along the valley line of the adjacent wires positioned in the lower layer, so that the number of turns of the wire positioned in the upper layer is smaller by one than the number of turns of the wire positioned in the lower layer, and the 6th, 8th, and 24th turns of the second wire W 2  corresponds to this. 
     In the present embodiment, when the numbers of turns of the respective first and second wires W 1  and W 2  are counted with the first and second terminal electrodes  41  and  42  as a starting point, the 1st to 6th turns constitute the first winding block B 1 , the 7th to 18th turns constitute the third winding block B 3 , and the 19th to 24th turns constitute the second winding block B 2 . However, at each of the 7th and 19th turns at which the wires cross each other, the wires are partially positioned in the crossing area CA 1  or CA 2 . 
     The 7th and 19th turns of the first and second wires W 1  and W 2  cross each other in the first and second crossing areas CA 1  and CA 2 . When the first and second wires W 1  and W 2  cross each other, the positional relationship between the first and second wires W 1  and W 2  is inverted before and after the crossing point. Specifically, when focusing on the same turns of the first and second wires W 1  and W 2 , in the first and second winding blocks B 1  and B 2 , the first wire W 1  is positioned on the left side (first flange part  21  side) in  FIG.  2   , and the second wire W 2  is positioned on the right side (second flange part  22  side) in  FIG.  2   ; whereas in the third winding block W 3 , the first wire W 1  is positioned on the right side (second flange part  22  side), and the second wire W 2  is positioned on the left side (first flange part  21  side). 
     In the present embodiment, the number of turns of each of the first and second wires W 1  and W 2  is six in both the first and second winding blocks B 1  and B 2  and is 12 in the third winding block B 3 . Accordingly, when focusing on the same turns of the first and second wires W 1  and W 2 , the number of pairs of the first and second wires W 1  and W 2  in which the first wire W 1  is positioned on the left side (second wire W 2  is on the right side) is 12, and the number of pairs of the first and second wires W 1  and W 2  in which the first wire W 1  is positioned on the right side (second wire W 2  is on the left side) is also 12, thus enhancing symmetry between signals flowing in the first and second wires W 1  and W 2 , with the result that excellent high-frequency characteristics can be obtained. 
     As illustrated in  FIG.  1   , in the present embodiment, the y-direction positions of the first and third terminal electrodes  41  and  43  connected with the first wire W 1  are the same, and the y-direction positions of the second and fourth terminal electrodes  42  and  44  connected with the second wire W 2  are the same. When viewed in the direction of the arrow V of  FIG.  1   , the first and third terminal electrodes  41  and  43  connected with the first wire W 1  are positioned on the right side, and the second and fourth terminal electrodes  42  and  44  connected with the second wire W 2  are positioned on the left side. Thus, when the first and second wires W 1  and W 2  are wound clockwise as viewed in the direction of the arrow V with the first and second terminal electrodes  41  and  42  as the starting point, the first wire W 1  is positioned on the left side (first flange part  21  side) in  FIG.  2   , and the second wire W 2  is positioned on the right side (second flange part  22  side) in  FIG.  2    in the first winding block B 1  when focusing on the same turns of the first and second wires W 1  and W 2  unless the wires are made to cross each other. The first and second wires W 1  and W 2  do not cross each other in the first winding block B 1 , so that the above positional relationship is maintained over the entire area of the first winding block B 1 . 
     When the first and second wires W 1  and W 2  are made to cross each other in the first crossing area CA 1 , the positional relationship between the first and second wires W 1  and W 2  is inverted. Thus, in the third winding block B 3 , the first wire W 1  is positioned on the right side (second flange part  22  side) in  FIG.  2   , and the second wire W 2  is positioned on the left side (first flange part  21  side) in  FIG.  2    when focusing on the same turns of the first and second wires W 1  and W 2 . In the third winding block B 3 , the first and second wires W 1  and W 2  do not cross each other, so that the above relationship is maintained over the entire third winding block B 3 . 
     When the first and second wires W 1  and W 2  are made to cross each other in the second crossing area CA 2 , the positional relationship between the first and second wires W 1  and W 2  is inverted once again. Thus, in the second winding block B 2 , the first wire W 1  is positioned on the left side (first flange part  21  side) in  FIG.  2   , and the second wire W 2  is positioned on the right side (second flange part  22  side) in  FIG.  2    when focusing on the same turns of the first and second wires W 1  and W 2 . In the second winding block B 2 , the first and second wires W 1  and W 2  do not cross each other, so that the above relationship is maintained over the entire second winding block B 2 . 
     As described above, when viewed in the direction of the arrow V of  FIG.  1   , the third terminal electrode  43  is positioned on the right side, and the fourth terminal electrode  44  is positioned on the left side, so that, as illustrated in  FIG.  3    which is a schematic view of the winding layout, it is possible to connect the terminal ends of the respective first and second wires W 1  and W 2  to the third and fourth terminal electrodes  43  and  44 , respectively, without making the first and second wires W 1  and W 2  cross each other any more. 
     Thus, in the common mode filter  10  according to the present embodiment, the number of the winding blocks is set to three, and the number of crossing times between the wires is set to two, so that the positional relationship between the first and second wires W 1  and W 2  is the same between the first winding block B 1  and second winding block B 2 . Therefore, conditions of one and the other end portions of the first and second wires W 1  and W 2  coincide with each other. This prevents occurrence of unbalance due to difference in the conditions of the wire end portions, making it possible to enhance high-frequency characteristics such as reflection characteristics (return loss) or noise conversion characteristics. 
     On the other hand, assuming that the number of the winding blocks is set to an even number (e.g., two), and the number of the wire crossing times is set to an odd number (e.g., one), the positional relationship between wires in the wiring area closest to the first flange part  21  and the positional relationship between the wires in the winding area closest to the second flange part  22  are inverse to each other. Thus, in order to connect the terminal ends of the respective first and second wires W 1  and W 2  to the third and fourth terminal electrodes  43  and  44 , respectively, it is necessary to make the first and second wires W 1  and W 2  cross each other once again so as to restore the positional relationship to its original state. 
       FIG.  4    is a schematic view for explaining a state where the last turns of the respective first and second wires W 1  and W 2  cross each other in a common mode filter of a comparative example. 
     As illustrated in  FIG.  4   , when viewed in the direction of the arrow V, the first terminal electrode  41  is positioned on the right side, and the second terminal electrode  42  is positioned on the left side, so that when the first and second wires W 1  and W 2  are wound clockwise without being made to cross each other, the first wire W 1  is positioned on the first flange part  21  side, and the second wire W 2  is positioned on the second flange part  22  side. This positional relationship is inverted every time the wires cross each other. However, when the number of the wire crossing times is an odd number, the inverted state is maintained in the winding block closest to the second flange part  22 , with the result that the first wire W 1  is positioned on the second flange part  22  side, and the second wire W 2  is positioned on the first flange part  21  side. When connecting the terminal ends of the respective first and second wires W 1  and W 2  respectively to the third and fourth terminal electrodes  43  and  44  in this state, the last turns of the respective first and second wires W 1  and W 2  cross each other as denoted by the arrow C since the third terminal electrode  43  is positioned on the right side, and the fourth terminal electrode  44  is positioned on the left side as viewed in the direction of the arrow V. 
     When the distance between the third and fourth terminal electrodes  43  and  44  in the y-direction is large as illustrated in  FIG.  5   , the last turns of the respective first and second wires W 1  and W 2  do not cross each other apparently as viewed from above (as viewed in the z-direction). However, in this case, as illustrated in  FIG.  6   , the first and second wires W 1  and W 2  cross each other on the xz surface of the winding core part  23 . That is, at any rate, when the last turns of the respective first and second wires W 1  and W 2  are made to cross each other, there occurs a necessity of restoring the positional relationship between the first and second wires W 1  and W 2  to its original state. 
     As described above, when the number of the wire crossing times in the areas between the winding blocks is an odd number, the 1st turns of the respective first and second wires W 1  and W 2  positioned on one end side do not cross each other, but the last turns positioned on the other end side cross each other. Thus, in the first and second wires W 1  and W 2 , there occurs a difference between a capacitance component generated at the one end side and that generated at the other end side, and this unbalance can cause deterioration in high-frequency characteristics such as reflection characteristics. However, in the common mode filter  10  according to the present invention, the number of the winding blocks is set to three (odd number), and the number of the wire crossing times is set to two (even number) in the areas between the winding blocks, so that the unbalance does not occur. As a result, high-frequency characteristics such as reflection characteristic can be enhanced. 
     As described above, in the common mode filter  10  according to the present embodiment, the number of the winding block is set to three (odd number) , and the number of the wire crossing times is set to two (even number) , so that conditions of one and the other end portions of the first and second wires W 1  and W 2  coincide with each other. This prevents occurrence of unbalance due to difference in the conditions of the wire end portions, making it possible to enhance high-frequency characteristics such as reflection characteristics (return loss) or noise conversion characteristics. 
     In addition, in the present embodiment, the number of turns in the first winding block B 1  and the number of turns in the second winding block B 2  are equal to each other, so that symmetry between the first and second winding blocks B 1  and B 2  positioned on both sides can be enhanced. This can eliminate product directionality. Further, in the present embodiment, the total number of turns in the first and second winding blocks B 1  and B 2  and the number of turns in the third winding block B 3  are equal to each other, so that the number of pairs of the first and second wires W 1  and W 2  in which the first wire W 1  is positioned on the left side (first flange  21  side) and the second wire W 2  is positioned on the right side (second flange  22  side) and the number of pairs of the first and second wires W 1  and W 2  in which the first wire W 1  is positioned on the right side (second flange  22  side) and the second wire W 2  is positioned on the left side (first flange  21  side) coincide with each other. This enhances symmetry between signals flowing in the first and second wires W 1  and W 2 , with the result that excellent high-frequency characteristics can be obtained. 
     Further, in the present embodiment, the second wire W 2  is wound over the first wire W 1 , so that wire winding density is enhanced. This can reduce the size of the winding core part  23  in the axial direction (x-direction). 
     Hereinafter, some modifications of the common mode filter  10  will be described. The structures of the modifications described below are also included in the scope of the present invention. 
       FIG.  7    is a schematic view for explaining the winding layout of a common mode filter  10 A according to a first modification. 
     The common mode filter  10 A illustrated in  FIG.  7    differs from the common mode filter  10  according to the above embodiment in that, in the third winding block B 3 , the second wire W 2  is positioned in the first winding layer S 1  (lower layer), and the first wire W 1  is positioned in the second winding layer S 2  (upper layer). As exemplified in the first modification, the vertical positional relationship between the first and second wires W 1  and W 2  in the first and second winding blocks B 1  and B 2  and that in the third winding block B 3  may be inverted. This brings about an advantage that the lengths of the first and second wires W 1  and W 2  are substantially equal to each other. 
       FIG.  8    is a schematic view for explaining the winding layout of a common mode filter  10 B according to a second modification. 
     In the common mode filter  10 B according to the second modification, the third winding area A 3  of the winding core part  23  is divided into fourth to sixth winding areas A 4  to A 6  and third and fourth crossing areas CA 3  and CA 4 . The fourth to sixth winding area A 4  to A 6  are arranged in this order as viewed from the first winding area A 1  to constitute fourth to sixth winding blocks B 4  to B 6 , respectively. 
     The numbers of turns in the first, second, and fifth winding blocks B 1 , B 2 , and B 5  are each four, and the numbers of turns in the fourth and sixth winding blocks B 4  and B 6  are each six. The first and second wires W 1  and W 2  cross each other in the first to fourth crossing areas CA 1  to CA 4 . Thus, when focusing on the same turns of the first and second wires W 1  and W 2 , the first wire W 1  is positioned on the left side (first flange part  21  side) in  FIG.  8   , and the second wire W 2  is positioned on the right side (second flange part  22  side) in  FIG.  8    in the first, second, and fifth winding blocks B 1 , B 2 , and B 5  at odd-numbered positions; whereas the first wire W 1  is positioned on the right side (second flange part  22  side), and the second wire W 2  is positioned on the left side (first flange part  21  side) in the fourth and sixth winding blocks B 4  and B 6  at even-numbered positions. 
     The number of turns of each of the first and second wires W 1  and W 2  is four in the first, second, and fifth winding blocks B 1 , B 2 , and B 5  at odd-numbered positions and is six in the fourth and sixth winding blocks B 4  and B 6  at even-numbered positions, so that when focusing on the same turns of the first and second wires W 1  and W 2 , the number of pairs of the first and second wires W 1  and W 2  in which the first wire W 1  is positioned on the left side (second wire W 2  is on the right side) is 12, and the number of pairs of the first and second wires W 1  and W 2  in which the first wire W 1  is positioned on the right side (second wire W 2  is on the left side) is also 12. 
     As exemplified in the second modification, the number of the winding blocks need not necessarily be three, but may be five. That is, when an odd number of the winding blocks are constituted, and the first and second wires W 1  and W 2  are made to cross each other in the areas between winding blocks axially adjacent to each other, the number of crossing times becomes an odd number, so that conditions of one and the other end portions of the first and second wires W 1  and W 2  can be made to coincide with each other. 
       FIG.  9    is a schematic view for explaining the winding layout of a common mode filter  10 C according to a third modification. 
     The common mode filter  10 C illustrated in  FIG.  9    differs from the common mode filter  10 B according to the second modification in that, in the fourth and sixth winding blocks B 4  and B 6 , the second wire W 2  is positioned in the first winding layer S 1  (lower layer), and the first wire W 1  is positioned in the second winding layer S 2  (upper layer). This brings about an advantage that the lengths of the first and second wires W 1  and W 2  are substantially equal to each other, as in the first modification. 
     It is apparent that the present invention is not limited to the above embodiments, but may be modified and changed without departing from the scope and spirit of the invention. 
     For example, in the above embodiment, the first and second wires W 1  and W 2  are each wound in a direction from the 1st turn to the 24th turn at the time of manufacture; however, conversely, they may be wound in a direction from the 24th turn to the 1st turn. 
     Further, although all the winding blocks have the double layer structure in the above embodiment, the first and second wires W 1  and W 2  may be wound in a bifilar manner in some or all of the winding blocks.