Coil assembly including common-mode choke coil

A coil assembly for reducing variations in characteristic impedance includes a winding section having a first surface and a second surface on the opposite side of the winding section from the first surface, a plurality of first protrusions provided on the first surface, and a plurality of second protrusions provided on the second surface. These protrusions are identical in shape to each other and are arrayed linearly on their respective surfaces so that the first protrusions are offset from the second protrusions. Two conducting wires are wound between neighboring protrusions such that one wire contacts one of the neighboring protrusions, while the other wire contacts the other neighboring protrusion.

BACKGROUND OF THE INVENTION

The present invention relates to a coil assembly such as a common-mode choke coil.

Recently, high-frequency transmission signals are becoming commonplace in such interface standards as the USB 2.0 standard, a high-speed interface for personal computers and the like, and the HTMI standard, a digital video and audio input/output interface for digital video and the like. In accordance with using high-frequency transmission signals, these standards employ a differential transmission method that reduces the effects of noise interference and signal error by transmitting signals in opposite phase along two conducting wires.

In reality, however, common-mode noise currents are often generated due to differences in the communication properties of the two conducting wires, for example. In such a case, the wires may act as antennas and radiate noise. Japanese patent application publication No. 2003-133148 proposes one common-mode choke coil for reducing this noise.

Further, in interfaces employing high-frequency transmission signals, in addition to inductance, the line-to-line capacitance of the common-mode choke coils remarkably influences the characteristic impedance of the coils.

SUMMARY OF THE INVENTION

However, the present inventors recognized that the common-mode choke coil disclosed in Japanese patent application publication No. 2003-133148 has no parts for positioning the conducting wires when winding the wires around the winding section. Therefore, the winding is not uniform, producing variations in line-to-line capacitance that cause variations in the characteristic impedance of the common-mode choke coil.

To reduce these variations, the present inventors found that the line-to-line capacitance changes based on the distance between the two conducting wires. Therefore, it is an object of the present invention to provide. a coil assembly that can reduce variations in characteristic impedance by maintaining a uniform interval between conducting wires.

This and other objects of the present invention will be attained by providing a coil assembly including an improved core, two conducting wires, and electrodes. The core includes a columnar winding section having a winding surface, and flanges disposed on both ends of the winding section. The two conducting wires are wound around the winding surface of the core. The electrodes are disposed on the flanges of the core to be connected to the two conducting wires. The winding section has a plurality of protrusions protruding from the winding surface. The two conducting wires are wound about the winding surface so as to pass between neighboring protrusions while remaining separated from each other.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A common-mode choke coil1which is one of the examples of a coil assembly according to a preferred embodiment of the present invention will be described while referring toFIGS. 1 through 4. As shown inFIG. 1, the common-mode choke coil1includes a core2, a first conducting wire6, a second conducting wire7, and a first electrode part8, and a second electrode part9.

The core2includes a winding section3, a first flange4, and a second flange5. The winding section3is formed of a magnetic body and has a substantially rectangular-shaped cross-section in a plane orthogonal to a longitudinal direction of the winding section3. The first flange4and second flanges5are disposed one on either longitudinal end of the winding section3and have shapes nearly identical with each other. As shown inFIG. 2, the longitudinal direction of the winding section3, which is the winding direction for the conducting wires6and7, is defined as an x-direction, and a latitudinal direction of the winding section3, equivalent to the direction connecting a first electrode8A to a second electrode8B described later, is defined as a y-direction. As shown inFIG. 3, a thickness direction of the winding section3orthogonal to the x-direction and the y-direction is defined as a z-direction.

As shown inFIGS. 2 and 3, the winding section3is configured of a first surface31extending in the widthwise direction (x-y direction), a second surface32on the side of the winding section3opposite the first surface31, and a first side surface33and a second side surface34extending in the thickness direction (x-z direction) between the first surface31and second surface32. The first surface31and second surface32are substantially parallel to each other, and the first side surface33and second side surface34are substantially parallel to each other. Hence, a cross-section of the first side surface33along the y-z plane is substantially rectangular in shape.

As shown inFIGS. 1,2and4, a first notch33ais formed in the first side surface33near an area that the first side surface33intersects with a back surface42described later. The first notch33ais a slight depression in the first side surface33and is formed across nearly the entire z-direction. A first corner33bis provided at a juncture between the first notch33aand the back surface42. A second corner33cis formed at a juncture between the first side surface33and the first notch33aas a step part. Similarly, as shown inFIGS. 1,2and4, a second notch34aidentical to the first notch33ais formed in the second side surface34where the second side surface34intersects a back surface52described later. A third corner34bis provided at a juncture between the second notch34aand the back surface52. A fourth corner34cis formed at a juncture between the second side surface34and second notch34aas a step part.

As shown inFIGS. 2 and 3, first protrusions31A-31D are arrayed linearly at regular intervals in the x-direction across the approximate center region of the first surface31with respect to the y-direction. As shown inFIGS. 3 and 4, second protrusions32A-32C are disposed substantially in the center of the second surface32with respect to the y-direction and arrayed linearly at regular intervals in the x-direction. All of the first protrusions31A-31D and second protrusions32A-32C have substantially the same shape, tapering from a base end toward a top end such that the cross-sectional area of the base end is greater than that of the top end (seeFIG. 3). Further, these protrusions are shaped into a gentle mountain shape avoiding overhanging configuration as viewed in z-direction. The surfaces of the protrusions are sloped with respect to the surfaces of the winding section3.

As shown inFIG. 3, the second protrusion32A is positioned substantially between the first protrusions31A and31B in the x-direction. As shown inFIGS. 2 and 4, a first region3A is defined between the first protrusions31A and31B, a second region3B is defined between the second protrusions32A and32B, a third region3C is defined between the first protrusions31B and31C, a fourth region3D is defined between the second protrusions32B and32C, and a fifth region3E is defined between the first protrusions31C and31D.

As shown inFIGS. 2 and 3, the first flange4is substantially shaped as a rectangular parallelepiped formed by a front surface41and back surface42orthogonal to the x-direction, a first side surface43and second side surface44orthogonal to the y-direction, and a top surface45and a bottom surface46orthogonal to the, z-direction. Similarly, the second flange5is substantially shaped as a rectangular parallelepiped formed by a front surface51and back surface52orthogonal to the x-direction, a first side surface53and second side surface54orthogonal to the y-direction, and a top surface55and a bottom surface56orthogonal to the z-direction.

As shown inFIG. 2, a pair of first and second grooves45aand45bis formed in the top surface45sloping from a substantially central position on the top surface45in the x-direction toward the winding section3. The first and second grooves45aand45bare symmetrical about a line in the x-direction passing through a central point in the top surface45with respect to the y-direction. A first retaining part45A is defined as a step formed by the first groove45aon the side of the first groove45anear the first side surface33in the y-direction. A second retaining part45B is defined as a step formed between the second groove45band the first groove45a.

Similarly, a pair of third and fourth grooves55aand55bis formed in the top surface55of the second flange5sloping from a substantially central position on the top surface55in the x-direction toward the winding section3. The third and fourth grooves55aand55bare symmetrical about a line in the x-direction passing through a central point in the top surface55with respect to the y-direction. A third retaining part55A is defined as a step formed by the third groove55aon the side of the third groove55anear the second side surface34in the y-direction. A fourth retaining part55B is defined as a step formed between the fourth groove55band the third groove55a.

The first electrode part8includes a first electrode8A and a second electrode8B those arrayed in the y-direction. The first electrode8A is on the first side surface43side and a second electrode8B is on the second side surface44side. As shown inFIG. 1, the first and second electrodes8A and8B are formed by electroplating either side of the top surface45and front surface41. A portion of the first electrode8A is formed in the first groove45ain the top surface45. Similarly, a portion of the second electrode8B is formed in the second groove45b. The top surface45portion of the first electrode part8is the part that connects with the conducting wires6and7.

As shown inFIG. 2, the second electrode part9, like the first electrode part8, includes a third electrode9A on the first side surface53side and a fourth electrode9B on the second side surface54side and aligned in the y-direction. The third and fourth electrodes9A and9B are formed by electroplating either side of the top surface55and front surface51. A portion of the third electrode9A is formed in the third groove55ain the top surface55. Similarly, a portion of the fourth electrode9B is formed in the fourth groove55b.The top surface55portion of the second electrode part9connects with the conducting wires6and7. The second flange5is formed nearly identical to the first flange4and is symmetrical to the first flange4across the winding section3. Therefore, the direction connecting the first electrode8A to the second electrode8B is substantially the same as the direction connecting the third electrode9A to the fourth electrode9B.

As shown inFIG. 2, the first conducting wire6has ends6A and6B. With the end6A connected to the first electrode8A, the first conducting wire6is disposed in the first groove45aand engaged with the first retaining part45A. The first conducting wire6is then led over the back surface42toward the first notch33aside, and is run through the first notch33aalong the first corner33b. From this point the first conducting wire6begins its winding around the winding section3.

The second conducting wire7includes ends7A and7B. With the end7A connected to the second electrode8B, the second conducting wire7is disposed in the second groove45band engaged with the second retaining part45B. The second conducting wire7then extends toward the first notch33a, passing near the first protrusion31A on the first surface31, and is led through the first notch33aalong the second corner33c.From this point the second conducting wire7begins its winding around the winding section3. By winding the first conducting wire6along the first corner33band the second conducting wire7along the second corner33c, the start positions for winding the conducting wires6and7can be accurately regulated so that the windings are less likely to shift to become in disarray. Further, the conducting wires6and7can be accurately run from their points of connection to the first notch33aby engaging the conducting wires6and7with the first retaining part45A and second retaining part45B to lead these wires to the first notch33a, respectively.

As shown inFIG. 4, the second conducting wire7disposed along the second corner33cis wound over the surface of the second surface32on the first flange4side of the second protrusion32A and is wound over the second side surface34to the first surface31side. Next, as shown inFIG. 2, the second conducting wire7wound up from the second side surface34passes through the first region3A of the first surface31so as to contact the first protrusion31B and is subsequently wound over the first side surface33to the second surface32side.

Further, as shown inFIG. 4, the first conducting wire6disposed along the first corner33bis subsequently run over the second surface32, and wound over the second side surface34to the first surface31side. Next, as shown inFIG. 2, the first conducting wire6wound up from the second side surface34passes through the first region3A of the first surface31so as to contact the first protrusion31A and is subsequently wound around to the second surface32side.

The interval between center points of the first protrusion31A and first protrusion31B in the x-direction is a fixed distance T. Since the first protrusions31A and31B have the same shape, the distance between the conducting wires6and7within the first region3A is maintained at a uniform distance t1.

As shown inFIG. 4, the second conducting wire7wound through the first region3A and over the first side surface33to the second surface32is then run through the second region3B on the second surface32so as to contact the second protrusion32B, and is subsequently wound over the second side surface34to the first surface31. The first conducting wire6also wound through the first region3A and over the first side surface33to the second surface32side is run through the second region3B on the second surface32so as to contact the second protrusion32A, and is subsequently wound over the second side surface34to the first surface31side.

The second region3B is formed substantially identical to the first region3A so that the distance between center points of the second protrusions32A and32B is equivalent to the distance between center points of the first protrusions31A and31B, that is, the distance T. Since the second protrusions32A and32B are identical in shape to the first protrusion31A, the second region3B is substantially identical in shape to the first region3A. Accordingly, the distance between the conducting wires6and7in the second region3B is identical to the distance between the conducting wires6and7in the first region3A, that is, t1.

Similarly, since the third region3C, fourth region3D, and fifth region3E are also formed substantially identical to the first region3A, the distance between the conducting wires6and7in the regions3C,3D, and3E are maintained at the same value t1. Hence, when winding the conducting wires6and7about the winding section3through these regions, the distance in the x-direction is maintained at a uniform t1so that the same space is maintained between the conducting wires.

As shown inFIG. 2, the first region3A, third region3C, and fifth region3E on the first surface31are partitioned by the first protrusions31B and31C having the same shape. As shown inFIG. 4, the second region3B and fourth region3D on the second surface32are partitioned by the second protrusion32B. Since all of the first protrusions31A-31D and second protrusions32A-32C have substantially the same shape, the distance between neighboring regions is substantially identical.

Further, the conducting wires6and7are arranged in these regions so as to contact the protrusions partitioning the regions. Therefore, the distance between a group of conducting wires6and7arranged in the first region3A and the group of conducting wires6and7arranged in the third region3C is t2, while the distance between the group of conducting wires6and7in the third region3C and the group of the conducting wires6and7in the fifth region3E is a substantially equivalent t2. Further, the distance between the group of conducting wires6and7in the first region3A and the group of conducting wires6and7in the third region3C is substantially equivalent to the distance between the group of conducting wires6and7in the second region3B and the group of conducting wires6and7in the fourth region3D.

Therefore, when winding the conducting wires6and7around the winding section3, the distance between each turn measured for the conducting wires6and7as a set is at least the fixed value from the first region3A to the fifth region3E, that is, t2.

As shown inFIG. 4, the second conducting wire7extending from the fifth region3E over the first side surface33is wound over to the second surface32side. The second conducting wire7extends over the second surface32toward the second notch34aand is run to the position of the third corner.34b.Subsequently, the second conducting wire7is led through the second notch34aalong the third corner34b.As shown inFIG. 2, the second conducting wire7is then disposed on the back surface52and engaged with the third retaining part55A. The second conducting wire7runs through the third groove55aand extends to the third electrode9A side with the end7B connected to the third electrode9A.

As shown inFIG. 4, the first conducting wire6extending from the fifth region3E over the first side surface33is wound over to the second surface32side. The first conducting wire6extends over the second surface32along the second flange5side of the second protrusion32C toward the second notch34aand is positioned at the fourth corner34c. Subsequently, the first conducting wire6is led through the second notch34aalong the fourth corner34c. As shown inFIG. 2, the first conducting wire6is run over the first surface31in close proximity to the first protrusion31D and is engaged with the fourth retaining part55B. The first conducting wire6is led through the fourth groove55band extends to the fourth electrode9B side so that the end6B is connected to the fourth electrode9B.

By winding the first conducting wire6along the fourth corner34ctoward the connection point and winding the second conducting wire7along the third corner34btoward its connection point, the ending positions of the conducting wires6and7are precisely defined. Further, by engaging the conducting wires6and7extending from the second notch34awith the fourth retaining part55B and third retaining part55A, respectively, for connecting the ends of the conducting wires6and7to the connection points, precise positioning of the end portions of the conducting wires6and7between the second notch34aand the connection points is achievable.

Further, when winding the conducting wires6and7around the winding section3, there may be cases in which, for example, the first conducting wire6is wound on the top surface or sloping surface of the first protrusion31A. However, since the surface of the first protrusion31A is sloped, the first conducting wire6slides down the surface of the first protrusion31A and falls at the foot or base of the first protrusion31A where the first protrusion31A intersects the first surface31. Hence, by winding the conducting wires6and7about the winding section3so as to catch slightly on the first protrusions31A-31D and the second protrusions32A-32C, the conducting wires6and7can be wound so as to properly contact the feet of these protrusions.

In the common-mode choke coil1having the construction described above, the distance between the conducting wires6and7is maintained at a substantially uniform value t1, while the distance of one turn for the group of conducting wires6and7is maintained at a substantially uniform value t2. Hence, variation in property among produced common-mode choke coils can be reduced.

Since the common-mode choke coil1described above can accurately regulate the starting positions and ending positions of the conducting wires6and7wound about the winding section3, the structure of the common-mode choke coil1can reduce variations in properties among different products. Further, in the common-mode choke coil1described above, the first and second flanges4and5are shaped identical to one another and are symmetrical about a center position of the winding section3in the x-y plane. Accordingly, when manufacturing the common-mode choke coil1, the pair of flanges provided on both ends of the winding section3can both be the first flange4. Hence, it is not necessary to align the core2in the x-direction when manufacturing the common-mode choke coil1, eliminating unnecessary steps and improving productivity.

Since the first notch33ais formed along the juncture between the winding section3and the first flange4, the conducting wires6and7can be wound from the end of the winding section3on the first flange4side, effectively utilizing the winding section3. Further, by forming the juncture between the first flange4and winding section3as a portion of the first notch33a, the shape of the core2is simplified, facilitating molding of the core2.

Further, since the second notch34ais formed along the juncture between the winding section3and second flange5, the conducting wires6and7can be wound all the way to the end of the winding section3on the second flange5side, thereby more effectively utilizing the winding section3.

The line-to-line capacitance of the common-mode choke coil1varies according to the distance between the conducting wires6and7and the distance between each turn of the set of conducting wires6and7. In this standpoint, the common-mode choke coil1of the preferred embodiment maintains these distances at uniform values for each product. Thus, a common-mode choke coil having substantially uniform line-to-line capacitance can be provided. Further, the characteristic impedance of the common-mode choke coil varies according to line-to-line capacitance. In this standpoint, the variation of line-to-line capacitance among products is reduced by maintaining the distance between the conducting wires6and7at a uniform t1and the distance between each turn of the set of conducting wires6and7at a uniform t2. Thus, a common-mode choke coil with uniform characteristic impedance for each product can be provided. Accordingly, the resultant common-mode choke coil provides less variation in characteristic impedance among products and is capable of reliably removing specific frequencies.

Next, several modifications to the preferred embodiment will be described. The protrusions can be formed only on the first surface31or only on the first side surface43. Alternatively, protrusions can be provided on each of the first surface31, second surface32, and first side surface43. By providing protrusions on at least one surface among the four surfaces and winding the conducting wires6and7at the feet of these protrusions, it is possible to maintain a uniform distance between the conducting wires6and7and between each turn of the set of conducting wires6and7.

When providing both the first and second protrusions on the first surface31and first side surface33, respectively, it is possible to maintain a uniform distance between the conducting wires6and7and between each turn of the set of conducting wires6and7by displacing the first and second protrusions at about ¼ pitch in the x-direction. Similarly, the first and second protrusions may be provided on the second surface32and second side surface34, respectively.

Further, in the preferred embodiment described above, both the first and second protrusions are provided at equal intervals in a direction parallel to the x-direction. However, it is also possible, for example, to offset the first protrusions on the first surface31in the y-direction. In the latter case, the positions of the first protrusions should be calculated in advance to maintain a uniform distance between the conducting wires6and7and between each turn of the set of conducting wires6and7.

Further, the winding section3may have a polygonal cross-section and include the first surface31. A plurality of first protrusions of identical shape may be provided on the first surface31and arranged linearly at fixed intervals in a direction from one of flange toward the other flange.

With this construction, it is possible to maintain a uniform distance between each turn of the conducting wires6and7and a uniform distance between the set of conducting wires6and7when winding the conducting wires6and7about the winding section3. Since the line-to-line capacitance varies according to the distance between the conducting wires6and7and the distance between each turn of the set of conducting wires6and7, this construction can maintain a uniform line-to-line capacitance of the conducting wires on the winding section3.

Further, the winding section3having a polygonal cross-section has a second surface, and the protrusions include a plurality of second protrusions provided on the second surface in addition to the first protrusions provided on the first surface. The second protrusions are identical in shape to each other and to the first protrusions and are arranged linearly at fixed intervals on the second surface in a direction from one flange toward the other flange. The first protrusions and the second protrusions may be arranged at positions offset from each other in the direction from one flange toward the other flange.

With this construction, it is possible to improve uniformity in distance between the conducting wires6and7and between each turn of the set of conducting wires6and7, thereby improving on uniformity in line-to-line capacitance of the conducting wires on the winding section.

While a common-mode choke coil has been described in detail with reference to specific embodiment thereof, it would be apparent to those skilled in the art that various modifications and variations may be made therein without departing from the spirit of the invention, the scope of which is defined by the attached claims.