JP2011124553A - Noise filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a noise filter which does not require a middle leg and can be miniaturized, in a small filter for reducing normal mode noise and common mode noise. <P>SOLUTION: The noise filter has two magnetic legs, a soft magnetic core having two flanges for connecting ends of the two magnetic legs, and coils prepared at each of the two magnetic legs. The peripheral part of the flange is extruded to the outside more than the outside exposed surface of the coil. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a small filter that reduces normal mode noise and common mode noise.

  In recent years, the performance of in-vehicle electronic devices has been improved. Furthermore, vehicles in which these in-vehicle electronic devices are connected to each other via an in-vehicle LAN network such as a LIN (Local Interconnect Network) or a CAN (Controller Area Network) are becoming common. For this reason, the number of ECUs (Electronic Control Units) mounted per vehicle has increased, and the number of electronic components has greatly increased. Under such circumstances, higher performance and smaller size are required for noise countermeasure components.

In general, as a noise countermeasure component of an electronic device, a component in which a coil is formed by winding a conductive wire around a core made of a soft magnetic material is used.
FIG. 7 shows an example of noise countermeasures using coil components. This is a noise filter using a common mode choke coil 11 using a soft magnetic toroidal core 12 and a normal mode choke coil 13 using a rod-like soft magnetic core 14. The common mode choke coil 11 is effective in reducing common mode noise between the lines AA ′ and GND, and the normal mode choke coil 13 is effective in reducing normal mode noise in the line AA ′.
The soft magnetic core 14 used for the normal mode choke coil 13 needs to have a DC superposition characteristic, and is preferably an Fe-based alloy soft magnetic material having a high saturation magnetic flux density. However, as shown in FIG. By doing so, the DC superposition characteristics can be improved and an inexpensive soft ferrite material can be used.

However, the configuration of FIG. 7 requires at least a common mode noise component and a normal mode component, and mounting a noise filter composed of the above requires a large area, which limits the downsizing of the mounted device. .
In order to solve the above problem, the function of the normal mode choke coil is added to the common mode choke coil described in Patent Document 1, and common mode noise and normal mode noise are dealt with by one coil component. The one is the common mode noise filter shown in FIG.

  In the common mode noise filter 20 of FIG. 8, the soft magnetic core 21 used has three magnetic legs, the middle leg 22 has a gap gap in part, the two side legs 23, 24 have coils 25, 26 are provided. In the common mode noise filter 20, the coil 25 or the coil 26 generates an impedance by the magnetic flux of the magnetic path 27 (indicated by a one-dot dashed line) having the side legs 23 and the side legs 24 as paths in the soft magnetic core 21 to be used. Reduce common mode noise. In addition, with respect to normal mode noise superimposed on each coil, the coil 25 and the coil 25 are caused by the magnetic flux in the magnetic path 28 (shown by dotted lines) having a common magnetic path as the middle leg 22 and the gap gap in the soft magnetic core 21. Impedance is generated at 26 to reduce normal mode noise.

  Patent Document 2 proposes further miniaturization by improving the insulation between the two coils of the common mode noise filter described in Patent Document 1.

JP 2005-116792 A JP 2008-5171 A

  The inventor focused on the size of the core in the core structure described in Patent Document 1 (FIG. 8) and studied to reduce the size, but due to the presence of a middle leg that is very effective in reducing normal mode noise, It came to the recognition that there is a limit to the conversion.

  In view of the above problems, the inventor has an object of providing a noise filter that can be reduced in size without a middle leg in a small filter that reduces normal mode noise and common mode noise.

  The inventor examines the core shape, and even if there is no core leg of the core, the effect of reducing both the normal mode noise and the common mode noise is remarkable by forming the flange portions at both ends of the magnetic leg. And since there is no middle leg, the present inventors have found a noise filter that can be further downsized.

The present invention provides a noise comprising: two magnetic legs; a soft magnetic core having two flange parts connecting the ends of the two magnetic legs; and a coil provided on each of the two magnetic legs. A filter,
The noise filter is characterized in that the peripheral portion of the flange portion protrudes outward from the outer exposed surface of the coil.
In the present invention, the area ratio F of the brim portion that projects outward from the outer exposed surface of the coil is
When F = (S−L) / S is defined,
(here,
S is a cross-sectional area perpendicular to the magnetic leg axis direction of the brim portion,
L is the total area of the coil part including the magnetic leg to the outermost periphery projected onto the flange part in the magnetic leg axis direction. )
It is a noise filter characterized by F ≧ 0.25.
Further, the present invention is a noise filter characterized by satisfying a relationship of a ≧ b ≧ 0.2a, where a and b are cross-sectional areas of the two magnetic legs, respectively.
Further, according to the present invention, the soft magnetic core has a split surface at a central portion in the axial direction of two magnetic legs, and the soft magnetic core divided into two by the split surface is plane-symmetric with respect to the split surface. In addition, the noise filter is characterized in that the two divided surfaces face each other over the entire surface.
The present invention is the noise filter characterized in that the number of turns of the coil in which the conducting wire is wound around each of the two magnetic legs and the sectional area of the conducting wire are equivalent.
The present invention also provides a noise filter, wherein the soft magnetic core is an MnZn ferrite core, and an insulating film is provided between the wound coil and the MnZn ferrite core.

According to the present invention, since the middle legs of the soft magnetic core as described in Patent Documents 1 and 2 are not required, the core shape and the filter shape can be further reduced as compared with the prior art.
The brim portions at both ends of the magnetic leg form a magnetic path between the opposite brim portions and the space, and have the function of the middle leg in the prior art.
Further, in the conventional structure, as shown in FIG. 8, since the coil portion protrudes from the core outer shape, the bobbin 29 having the flange portion is required to protect and fix the coil portion (FIG. 4 of Patent Document 1). 23, 24, 14b of FIG. 1 of Patent Document 2), the present invention eliminates the need for a bobbin and enables further miniaturization.

The perspective view of the noise filter of Example 1 of the present invention. Schematic from the a direction and b direction of the noise filter of Example 1 of the present invention. Characteristic diagram showing DC superposition characteristics of noise filter of embodiment 1 of the present invention Schematic from the a direction and b direction of the noise filter of Example 2 of the present invention. Schematic from the a direction and b direction of the noise filter of Example 3 of the present invention. Explanatory drawing showing coil connection state at the time of noise filter evaluation Schematic configuration diagram of a conventional noise filter Schematic configuration diagram of a conventional noise filter Explanatory drawing of area ratio S prescribed | regulated by this invention

  The present inventor has examined the structure of a small noise filter that is excellent in noise reduction effect for both normal mode noise and common mode noise, and by forming a flange portion at both ends of the two magnetic legs, As compared with the noise filter having the structure, the remarkable effect that further downsizing is possible has been found.

  Specifically, as shown in FIG. 6, two coils were connected, and inductance and DC resistance were measured. The inductance of the two coils connected in series is NML, the DC resistance is Rdc, the inductance of the two coils connected in parallel is CML, NML is 2 μH or more, CML is 25 μH or more, and Rdc is 5 mΩ or less. Various studies were made on the core shape, the number of turns of the coil, and the diameter of the conductive wire forming the coil. As a result, the external dimensions for satisfying the above specifications are as follows. In the configuration shown in FIG. 8, the length A in the magnetic leg direction is 26 mm, the length B in the orthogonal direction to the magnetic leg is 30 mm, and the height C is 21 mm is the limit (see comparative example), and there is a problem that it cannot be further downsized. The present inventor has found a configuration for realizing the miniaturization with respect to the problem that cannot be miniaturized. Here, the length A in the magnetic leg direction, the length B in the direction orthogonal to the magnetic leg, and the height C are as shown in FIG.

In the present invention, the flanges are formed continuously at both ends of the two magnetic legs over the two magnetic legs. Moreover, the peripheral part of the collar part protrudes outward from the outer exposed surface of the two coils that are wound. In the periphery of the flange portion that protrudes to the outside of the coil, a magnetic path is formed in which the gap between the flange portions forms a gap between the periphery of the opposite flange portions.
Therefore, since the brim portion functions as a part of the soft magnetic core, the larger the overhang from the coil outer exposed surface, the higher the magnetic path forming ability. The thickness of the brim portion is designed so that the magnetic flux is not saturated from the saturation magnetic flux density of the soft magnetic core material and the cross-sectional area of the brim portion connected to the two magnetic legs. Including the above, the shape of the soft magnetic core is appropriately determined in consideration of the size of the filter and the required noise reduction effect.

In the present invention, the area ratio F projecting outward from the outer exposed surface of the two wound coils of the plate-shaped brim portion is
When defined as F = (S−L)) / S,
(here,
S is a cross-sectional area perpendicular to the magnetic leg axis direction of the brim portion,
L is the total area of the coil part including the magnetic leg to the outermost periphery projected onto the flange part in the magnetic leg axis direction. )
The area ratio F, the cross-sectional area S perpendicular to the magnetic leg axis direction of the brim part, and the total L of the area up to the outermost periphery projected from the coil part including the magnetic leg to the brim part in the magnetic leg axis direction will be described. .
FIG. 9 will be described with reference to FIG. 2B as an example. S is represented by the product of the long side B and the short side C of the brim portion. The total area L up to the outermost periphery of the coil portion including the magnetic leg projected onto the collar portion in the magnetic leg axis direction is the mesh portion 15 in FIG. The lead portion of the coil is not included in the mesh portion. Therefore, (SL) is a portion obtained by subtracting the area of the mesh portion 15 from the area S (product of the long side B and the short side C) perpendicular to the magnetic leg axis direction of the collar portion of FIG. A hatched portion 16 is shown. Therefore, the area ratio F is the ratio of the shaded portion 16 to the area S (the product of the long side B and the short side C).
If F ≧ 0.25 is satisfied, an excellent noise reduction effect can be obtained for both normal mode noise and common mode noise.
More preferably, F ≧ 0.3, and the noise reduction effect is further increased.
Further, it is understood that F increases when the amount of protrusion of the flange portion becomes larger than the cross-sectional area of the magnetic leg and the coil winding portion. In this case, when assembling the noise filter or handling, There is a risk of chipping or cracking around the flange due to the stress of. For this reason, the upper limit of F is preferably less than 0.7.

  In the present invention, the two magnetic legs need not have the same cross-sectional area. That is, by reducing the cross-sectional area on one side, the size can be further reduced without causing deterioration of characteristics. That is, the size can be further reduced by examining the target filter shape (mounting area, filter volume) and the necessary noise reduction effect. Here, it is preferable to satisfy the relationship of a ≧ b ≧ 0.2a, where a and b are the cross-sectional areas of the two magnetic legs. If b is less than 0.2a, a sufficient noise reduction effect for common mode noise cannot be obtained. The cross-sectional shape of the magnetic leg need not be a circle, and an elliptical shape or a rounded rectangular shape is also possible in consideration of insulation between two coils. The rounded rectangle means a shape in which two long sides of a rectangle are sandwiched between two semicircles having the long side length as a diameter, as described in (Example 3) described later.

In the soft magnetic core of the present invention, the soft magnetic core having a split surface at an axially central portion of the two magnetic legs, the soft magnetic core divided into two by the split surface is plane-symmetric with respect to the split surface, and The two split surfaces preferably face each other over the entire surface.
With this structure, it is possible to easily assemble a coil wound in advance by inserting magnetic leg portions from both ends of the coil.
If necessary, a magnetic gap can be easily formed by inserting a nonmagnetic spacer between the two divided surfaces.

  In the noise filter of the present invention, it is preferable that the number of turns of the coil in which the conducting wire is wound around the two magnetic legs and the sectional area of the conducting wire are the same value. A sufficient noise reduction effect can be obtained by making the number of turns of the two coils equal to the cross-sectional area of the conducting wire with respect to the common mode noise.

  As the soft magnetic core, Mn-based or Ni-based ferrite is produced by firing after press molding, so that it has a high degree of freedom in shape and is preferable because it is inexpensive. Since Mn-based ferrite has a small specific resistance, it is preferable to use an insulating film in order to ensure sufficient insulation with the coil wound with the insulating film conductor.

  The insulating film is preferably an aramid paper such as Nomex (registered trademark) or a polyimide film such as Kapton (registered trademark) from the viewpoint of heat resistance and strength.

The present invention provides a noise comprising: two magnetic legs; a soft magnetic core having two flange parts connecting the ends of the two magnetic legs; and a coil provided on each of the two magnetic legs. A filter,
The noise filter is characterized in that the peripheral portion of the flange portion protrudes outward from the outer exposed surface of the coil.
In the present invention, the area ratio F of the brim portion that projects outward from the outer exposed surface of the coil is
When F = (S−L) / S is defined,
(here,
S is a cross-sectional area perpendicular to the magnetic leg axis direction of the brim portion,
L is the total area of the coil part including the magnetic leg to the outermost periphery projected onto the flange part in the magnetic leg axis direction. )
It is a noise filter characterized by F ≧ 0.25.
Further, the present invention is a noise filter characterized by satisfying a relationship of a ≧ b ≧ 0.2a, where a and b are cross-sectional areas of the two magnetic legs, respectively.
Further, according to the present invention, the soft magnetic core has a split surface at a central portion in the axial direction of two magnetic legs, and the soft magnetic core divided into two by the split surface is plane-symmetric with respect to the split surface. In addition, the noise filter is characterized in that the two divided surfaces face each other over the entire surface.
The present invention is the noise filter characterized in that the number of turns of the coil in which the conducting wire is wound around each of the two magnetic legs and the sectional area of the conducting wire are equivalent.
The present invention also provides a noise filter, wherein the soft magnetic core is an MnZn ferrite core, and an insulating film is provided between the wound coil and the MnZn ferrite core.

Hereinafter, the present invention will be described in detail based on examples. As a soft magnetic core material described below, MnZn ferrite core material MT30D manufactured by Hitachi Metals, Ltd. was used.
(Comparative example)
In the noise filter including the soft magnetic core shown in FIG. 8, in order to obtain NML = 2.5 μH, CML = 40.0 μH, and Rdc of 4.5 mΩ, the outer dimensions of A = 26 mm, B = 30 mm, and C = 21 mm are required. It was necessary. The size of the middle leg in the axial direction was 7 mm square.
Here, as shown in FIG. 6, NML, CML, and Rdc connect two coils, measure the inductance and DC resistance, and the inductance of the two coils connected in series is NML, and the DC resistance is Rdc, An inductance in which two coils are connected in parallel is CML.
The soft magnetic core is divided at the center part of the outer two magnetic legs so as to be plane-symmetric, and the outer parts of the base parts of the opposing magnetic legs are arranged so as to face each other on the entire divided surface. It is fixed with tape across the outside of the magnetic leg and bobbin.
Also, in order to obtain the inductance and Rdc of the NML and CML, a coil in which an insulating film conductor having a diameter of 1.8 mm was wound for 6 turns was formed on the bobbin, and the outer two magnetic legs were inserted into the coil bobbin. .

Example 1
A noise filter shape for obtaining NML = 2.5 μH, CML = 40.0 μH, and Rdc of 4.5 mΩ equivalent to the comparative example was examined.
As a result, as shown in FIG. 1 and FIG. 2 (schematic diagrams from directions a and b in FIG. 1), the shape is A = 24 mm, B = 30 mm, C = 20 mm, d (diameter of magnetic leg) = 11 mm, By winding 6 turns of the insulating film conductor 8 having a diameter of 1.8 mm around the two magnetic legs 2 and 3 of the soft magnetic core 1 having a thickness of the flanges 4 and 5 to form the coils 6 and 7, NML, CML, and Rdc equivalent to the comparative example were obtained.
In Example 1, the area ratio F described above is calculated. The cross-sectional area of the flange S = 30 mm × 24 mm = 720 mm ² and L = 334.8 mm ² (twice the area of the circle of diameter (11 mm + 1.6 mm + 1.6 mm)), so F = (S−L) / S = 0.535. Compared to the comparative example, A is 2 mm and C is 1 mm smaller. (B is the same value)
The soft magnetic core is divided at each central portion of the two magnetic legs so as to be plane-symmetric, and the outer portions of the two flange portions 4 and 5 facing each other so as to face each other on the entire divided surface. Two magnetic legs and the outside of the coil are sandwiched and fixed with tape. A polyimide film is sandwiched between the coils 6 and 7 and the flanges 4 and 5 and between the coils 6 and 7 and the magnetic legs 2 and 3 as an insulating film 9.
FIG. 3 shows DC superposition characteristics obtained by measuring NML of the noise filter of this example under conditions of a room temperature of 22 ° C., a frequency of 100 kHz, and an OSC level of 1V. It can be seen that the direct current value Idc = 70 A is close to 70 A, and no decrease in the inductance NML in which the two coils are connected in series is observed, indicating excellent direct current superposition characteristics.

(Example 2)
Compared to Example 1, the cross-sectional area of the magnetic leg was examined for further miniaturization. As a result, if the cross-sectional area of both of the two magnetic legs is reduced, the inductance of NML and CML is reduced and the characteristics are deteriorated as the cross-sectional area is reduced. It turned out that it does not change to NML and CML. Therefore, in Example 1, the diameter d of both magnetic legs is 11 mm. However, the diameter on only one side is reduced, and the limit at which equivalent characteristics can be obtained was investigated.
As a result, it was found that equivalent characteristics (NML = 2.5 μH, CML = 40.0 μH, Rdc 4.5 mΩ) can be obtained even when the diameter on one side is 11 mm and 4.92 mm. In this case, compared with the first embodiment, the coil diameter is reduced from 1.8 mm to 1.3 mm, and the number of turns is reduced by one from 6 to 5.
In Example 2, the area ratio F described above is calculated. The cross-sectional area of the flange portion S = 24 mm × 20 mm = 480 mm ² and L = 322.9 mm ² (total of the area of the circle of diameter (11 mm + 1.3 mm + 1.3 mm) and the area of the circle of diameter (4.92 mm + 1.3 mm + 1.3 mm) Therefore, it can be seen that F = (S−L) /S=0.327.
In addition, when the diameter of the magnetic leg of one side was made less than 4.92 mm, it turned out that CML reduces rapidly.
4, the diameter of the magnetic leg 2 is 11 mm (d1), the diameter of the magnetic leg 3 is 4.92 mm (d2), and the shape is A = 14 mm, B = 24 mm, C = 20 mm, the flange part 4, A filter was prepared by winding coils 2 and 2 on the two magnetic legs 2 and 3 of the soft magnetic core 1 having a thickness of 5 mm and winding the insulating film conductor 8 having a diameter of 1.3 mm for 5 turns. As in Example 1, the soft magnetic core is divided into two parts and fixed with tape.
Compared to the comparative example, A is 12 mm, B is 6 mm, and C is 1 mm smaller. Compared to Example 1, A is 10 mm and B is 6 mm smaller. (C is the same value.)
In Example 2, the cross-sectional shape of the two magnetic legs is a circle, but since the cross-sectional areas are different and the ratio of the diameters is 11: 4.92, the cross-sectional area ratio is 5: 1.
When the direct current superposition characteristics of the noise filter of Example 2 were measured under the same conditions as in Example 1, the results were the same as in Example 1.

(Example 3)
Compared to Example 2, the cross-sectional shape of the magnetic leg having a larger cross-sectional area among the two magnetic legs was examined for further miniaturization. As a result, it was found that further downsizing is possible by reducing the thickness of the magnetic leg in the B direction while keeping the cross-sectional area unchanged.
That is, as shown in FIG. 5, the shape is A = 14 mm, B = 22 mm, C = 20 mm, d11 = 9 mm, d12 = 12.5 mm, d2 = 4.92 mm, and the thickness of the flange portions 4 and 5 is 2 mm. Even in a filter produced by winding a coil 2 by winding 6 turns of an insulating film conductor 8 having a diameter of 1.3 mm around the two magnetic legs 2 and 3 of a certain soft magnetic core 1, equivalent characteristics: NML = 2.5 μH, CML = 40.0 μH and Rdc of 4.5 mΩ were obtained. Similar to the first embodiment, the soft magnetic core 1 is divided into two parts and fixed with tape.
In Example 3, the area ratio F described above is calculated. The flange cross-sectional area S = 22 mm × 20 mm = 440 mm ² and L = 190.7 mm ² (long side (9 mm + 1.3 mm + 1.3 mm) × short side 3.5 mm rectangle and diameter (9 mm + 1.3 mm + 1.3 mm)) Since it is the area and the sum of the areas of the circles having a diameter (4.92 mm + 1.3 mm + 1.3 mm), it can be seen that F = (S−L) /S=0.666, which is a large value.
In Example 3, the cross-sectional shape of the magnetic leg 3 having a small cross-sectional area out of the two magnetic legs 2 and 3 is a circle (diameter 5 mm), but the cross-sectional shape of the magnetic leg 2 having a large cross-sectional area is 3.5 mm. It has a shape in which two long sides of a rectangle of × 9 mm are sandwiched between semicircles with a diameter of 9 mm. This cross-sectional area is about 95 mm ^2, which is equivalent to a circle with a diameter of 11 mm in Examples 1 and ² .
In Example 2 and Example 3, the shape of the magnetic leg having a large cross-sectional area is different, but the cross-sectional area is about 95 mm ² and is equivalent.
Compared to the comparative example, A is 12 mm, B is 8 mm, and C is 1 mm smaller. Compared to Example 1, A is 10 mm and B is 8 mm smaller. (C is the same value.) Furthermore, B is 2 mm smaller than Example 2. (A and C are the same value.)
When the direct current superposition characteristics of the noise filter of Example 3 were measured under the same conditions as in Example 1, the results were the same as in Example 1.

Example 4
The soft magnetic core 1 according to the first embodiment is divided at the central portion of the two magnetic legs 2 and 3 so as to be plane-symmetrical, and outside the two flange portions 4 and 5 facing each other so as to face the entire divided surface. The parts were fixed with tape across the outer sides of the two magnetic legs 2 and 3 and the coils 6 and 7, but in Example 4, a press mold was used, and FIG. A soft magnetic core having the same shape as in Example 1 was obtained by press-molding MnZn ferrite granules in the direction of C dimension shown in FIG. A coil was formed on the soft magnetic core in the same manner as in Example 1 to produce a noise filter, and the same results as in Example 1 were obtained.
The core manufacturing method according to the fourth embodiment has a disadvantage that the number of coil forming steps is large because the coil needs to be wound directly around the core, but has an advantage that characteristic variation during mass production is reduced.

(Example 5)
The soft magnetic core 1 according to the first embodiment is divided at the central portion of the two magnetic legs 2 and 3 so as to be plane-symmetrical, and outside the two flange portions 4 and 5 facing each other so as to face the entire divided surface. The parts were fixed with tape across the outer sides of the two magnetic legs 2 and 3 and the coils 6 and 7, but in Example 5, (one side flange) and (2 magnetic legs + one side flange) The noise filter was manufactured using a soft magnetic core that can be divided asymmetrically. As a result, the same result as in Example 1 was obtained.

Table 1 shows NML, CML, Rdc, A, B, and C of Examples 1 to 3 and Comparative Example.

1 Soft magnetic core 2, 3 Magnetic legs
4, 5 brim
6, 7 Coil 8 Insulating film conductor 9 Insulating film 10 Noise filter

Claims (6)

A noise filter comprising two magnetic legs, a soft magnetic core having two flange parts connecting between the ends of the two magnetic legs, and a coil provided on each of the two magnetic legs. ,
The noise filter according to claim 1, wherein a peripheral portion of the flange portion protrudes outward from an outer exposed surface of the coil. An area ratio F of the brim portion that protrudes outward from the outer exposed surface of the coil,
When F = (S−L) / S is defined,
(here,
S is a cross-sectional area perpendicular to the magnetic leg axis direction of the brim portion,
L is the total area of the coil part including the magnetic leg to the outermost periphery projected onto the flange part in the magnetic leg axis direction. )
The noise filter according to claim 1, wherein F ≧ 0.25. 3. The noise filter according to claim 1, wherein a relationship of a ≧ b ≧ 0.2a is satisfied, where a and b are cross-sectional areas of the two magnetic legs, respectively. The soft magnetic core has a split surface at an axial center portion of two magnetic legs, the soft magnetic core divided into two by the split surface is plane-symmetric with respect to the split surface, and The noise filter according to claim 1, wherein the two divided surfaces face each other over the entire surface. The noise filter according to any one of claims 1 to 4, wherein the number of turns of a coil in which a conducting wire is wound around each of the two magnetic legs and the cross-sectional area of the conducting wire are equivalent. The noise filter according to any one of claims 1 to 5, wherein the soft magnetic core is a MnZn ferrite core, and an insulating film is provided between the wound coil and the MnZn ferrite core.

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