JP2006100465A - Coil and filter circuit using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coil capable of obtaining a sufficient impedance in a high frequency band of e.g. 150 kHz-30 MHz. <P>SOLUTION: The coil 10 comprises a first ferrite core 11, a second ferrite core 12, and coil conductors 13A, 13B integrally wound about those ferrite cores 11, 12. The second ferrite core has a frequency characteristic that the attenuation region of the permeability thereof exists on the higher frequency side of that of the first ferrite core. According to this configuration, the sufficient impedance can be obtained in the high frequency band of e.g. 150 kHz-30 MHz. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a coil and a filter circuit, and more particularly to a coil suitable for removing high-frequency noise and a filter circuit using the same.

  Conventionally, various noise filters using a toroidal coil in which a winding is provided on an annular core have been proposed.

  In a conventional toroidal coil, an Mn-Zn-based annular ferrite core is used as the annular core, and the magnetic permeability decreases and the inductance decreases in the high frequency band. As a result, the impedance decreases and high frequency noise is reduced. There was a problem that it could not be reduced sufficiently.

In order to solve such a problem, for example, a method in which a plurality of Mn—Zn-based annular ferrite cores are stacked in the radial direction has been proposed (see Patent Document 1). Further, a method has been proposed in which an annular ferrite core and an annular core made of an iron-based high permeability magnetic body are overlapped in the radial direction or the axial direction (see Patent Document 2).
Japanese Patent Laid-Open No. 5-121244 Japanese Patent No. 3163853

  In recent years, the influence of high frequency noise on electronic devices has become very large. For this reason, there is an increasing demand for suppressing high-frequency noise, and a standard called VCCI Class II exists as a standard for suppressing high-frequency noise of 150 kHz to 30 MHz.

  However, any of the above-described methods cannot obtain sufficient impedance in the high frequency band of 150 kHz to 30 MHz, and there is still room for improvement. Further, although it is possible to attenuate a wide range of 150 kHz to 30 MHz, which is the frequency band of the terminal noise voltage, by the noise canceller technique, it is still very difficult to sufficiently attenuate high frequency noise around 10 MHz. In addition, iron-based high magnetic permeability magnetic materials have a resistivity that is about five orders of magnitude smaller than that of Mn—Zn-based ferrites, so that sufficient insulation measures must be taken (for example, iron-based high magnetic permeability magnetic materials). An insulating coating is applied to the core made of or an insulating sheet is disposed between the substrate and the core).

  Therefore, an object of the present invention is to provide a coil capable of obtaining a sufficient impedance in a high frequency band of 150 kHz to 30 MHz, for example.

  Another object of the present invention is to provide a filter circuit capable of sufficiently reducing high-frequency noise in such a frequency band.

  As a result of repeated researches to achieve the above object, the inventor of the present application, for example, as a core material of a coil preferable for removing noise in a high frequency band of 150 kHz to 30 MHz, includes MzZn ferrite material and NiZn ferrite material. I found a combination. That is, the object of the present invention is to integrally wind the first ferrite core, the second ferrite core superimposed on the first ferrite core, and the first and second ferrite cores. The coil is turned, and the attenuation range of the magnetic permeability of the second ferrite core exists on the higher frequency side than the attenuation range of the magnetic permeability of the first ferrite core. Is done.

  In the present invention, it is preferable that the first ferrite core is made of a MnZn-based material and the second ferrite core is made of a NiZn-based material.

  In the present invention, the first ferrite core and the second ferrite core are overlapped in the axial direction, and the axial thickness of the first ferrite core is in the axial direction of the second core. It is preferable that it is thicker than the thickness. According to this, the cross-sectional area of the portion where the coil conductor is wound around the first ferrite core can be increased, and a large inductance value obtained due to the characteristics of the first ferrite core can be sufficiently secured. As a result, a sufficient impedance value can be secured.

  In the present invention, the first ferrite core and the second ferrite core are overlapped in the radial direction, and the first ferrite core is disposed on the inner side in the inner diameter direction of the second ferrite core. It is preferable. According to this, the magnetic path length of the portion where the coil conductor is wound around the first ferrite core can be shortened, and the large inductance value obtained due to the characteristics of the first ferrite core can be sufficiently obtained. As a result, a sufficient impedance value can be secured.

  The object of the present invention is also achieved by a filter circuit constructed using the above-described coil.

  The object of the present invention is also a filter circuit for reducing common mode noise propagating through the first and second conductive lines in the same phase, which is inserted in series in the first conductive line and electromagnetically connected to each other. First and second inductors coupled to each other, third and fourth inductors inserted in series in the second conductive line and electromagnetically coupled to each other, and the first and second inductors A first capacitor having one end connected to the connection point of the second capacitor, a second capacitor having one end connected to the connection point of the third and fourth inductors, and each of the first and second capacitors. A resonance circuit inserted between the end and the ground line, and the first to fourth inductors are configured using the coil according to any one of claims 1 to 8. According to the characteristic filter circuit Also it is achieved.

  According to the present invention, it is possible to provide a coil capable of obtaining a sufficient impedance in a high frequency band of 150 MHz to 30 MHz, for example.

  In addition, according to the present invention, it is possible to provide a filter circuit capable of sufficiently reducing high-frequency noise.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic perspective view showing the structure of a coil according to a preferred embodiment of the present invention. FIG. 2 is a schematic exploded perspective view of the coil shown in FIG. 1 and shows a state before winding.

  As shown in FIG. 1 and FIG. 2, the coil 10 includes a first ferrite core 11, a second ferrite core 12, and a coil wound integrally with the ferrite cores 11 and 12. It is comprised by conducting wire 13A, 13B.

  Both the first ferrite core 11 and the second ferrite core 12 are toroidal cores, and in the present embodiment, the first ferrite core 11 and the second ferrite core 12 are in the axial direction (the thickness direction of the core). ). The thickness T1 of the first ferrite core 11 is preferably set to be equal to or thicker than the thickness T2 of the second ferrite core 12 in the axial direction. In general, since the magnitude of the coil inductance L is proportional to the cross-sectional area of the coil, the coil lead wires 13A and 13B are wound around the first ferrite core 11 by increasing the thickness T1 of the first ferrite core 11. The cross-sectional area of the rotated portion can be increased, a large inductance value obtained due to the characteristics of the first ferrite core can be sufficiently secured, and the impedance value obtained as a result can be sufficiently secured. be able to. In consideration of the ease of winding of the coil conductor, the inner diameter φ12 of the first ferrite core 11 and the inner diameter φ22 of the second ferrite core 12 are preferably set to be the same.

  The first ferrite core is made of a MnZn-based ferrite material containing manganese and zinc as main components. The magnetic permeability of the first ferrite core formed by using such a material has a frequency characteristic that it is very high at a low frequency, but decreases significantly as the frequency becomes higher.

  On the other hand, the second ferrite core is made of a NiZn-based ferrite material containing nickel and zinc as main components. The magnetic permeability of the second ferrite core alone configured using such a material has a frequency characteristic that an attenuation region is present on the high frequency side as compared with the first ferrite core.

  The coil conductors 13A and 13B are integrally wound around the first and second ferrite cores 11 and 12 that are overlapped with each other. For example, when configuring a common mode choke coil, the common mode current is wound in a direction in which magnetic fluxes generated in the respective windings strengthen each other. In this way, common mode noise can be removed.

  As described above, the coil 10 according to the present embodiment is composed of a combination of the MnZn ferrite core and the NiZn ferrite core having different frequency characteristics, so that the impedance is large in the high frequency band of 150 kHz to 30 MHz. Is used as a filter, high frequency noise can be sufficiently reduced. In this embodiment, since a ferrite material is used, since the resistivity is higher than in the case of using an iron-based high permeability magnetic material as in the prior art, sufficient insulation can be ensured. . Further, as in the present embodiment, the second core made of NiZn ferrite material having a high resistivity is disposed on the lower side. Therefore, when the coil 10 is disposed on the substrate, there is no gap between other components and patterns. With this, sufficient insulation can be secured.

  In the present embodiment, the first and second ferrite cores have been described as having the same outer diameters φ11 and φ12, but the outer diameters of these cores may be different. In this embodiment, the case where the inner diameters φ12 and φ22 of the cores are the same has been described, but the inner diameters of the cores may be different.

  Next, a filter circuit using this coil 10 will be described in detail.

  FIG. 3 is a block diagram showing a configuration of a filter circuit according to a preferred embodiment of the present invention.

  As shown in FIG. 3, the filter circuit 20 includes a pair of input terminals 1A and 1B, output terminals 2A and 2B, and a ground terminal 5. This filter circuit further includes first and second inductors L1 and L2 inserted in series between one input terminal 1A and one output terminal 2A, the other input terminal 1B, and the other output terminal 2B. And third and fourth inductors L3 and L4 that suppress common mode noise in cooperation with the first and second inductors L1 and L2.

  The first to fourth inductors L1 to L4 are configured by the coil 10 described above. Specifically, the first to fourth inductors L1 to L4 are electromagnetically coupled to each other by a common core 14 that is a combination of the first ferrite core 11 and the second ferrite core 12 shown in FIG. One end of the coil conducting wire 13A wound integrally with the core 14 is a terminal 1A, the other end is 2A, one end of the coil conducting wire 13B is a terminal 1B, and the other end is 2B. Then, a connection point (intermediate connection portion P1) is provided in the middle of the winding 31 by the first coil conductor 13A, and the first end from one end of the winding 31 to the connection point P1 (winding portion 31a) is the first. And the second inductance L2 from the other end of the winding 31 to the connection point P1 (winding portion 31b). Similarly, for the third and fourth inductors L3 and L4, a connection point (intermediate connection portion P2) is provided in the middle of the winding 32 by the second coil lead wire 13B, and one end of the winding 32 is provided. The third inductor L3 is formed up to the connection point P2 (winding portion 32a), and the fourth inductor L4 is formed from the other end of the winding 32 to the connection point P2 (winding portion 32b).

  Here, in terms of performance as a filter, the inductances of the first and second inductors L1 and L2 are preferably the same value. The inductances of the third and fourth inductors L3 and L4 are preferably the same value. More preferably, all the inductances of the first and second inductors L1 and L2 and the third and fourth inductors L3 and L4 are set to the same value.

  Winding 31 (first coil conductor 13A) constituting first and second inductors L1 and L2, and winding 32 (second coil conductor constituting third and fourth inductors L3 and L4) 13B) are wound around a common core 14 as described above and are coupled to each other so as to cooperate and suppress common mode noise. That is, these windings are wound around the core 14 in such a direction that magnetic fluxes induced in the core 11 are canceled by the currents flowing through the windings when a normal mode current flows through them. Thus, the windings 31 and 32 and the core 14 constitute a common mode choke coil that allows a normal mode signal to pass while suppressing common mode noise.

  The filter circuit 20 further includes a first capacitor C1 having one end connected to the intermediate connection portion P1, a second capacitor C2 having one end connected to the intermediate connection portion P2, and first and second capacitors having one end connected to the intermediate connection portion P2. And a resonance circuit 41 connected to the other end of each of C1 and C2 and having the other end connected to the ground terminal 5. The resonance circuit 41 according to the present embodiment is an LCR parallel resonance circuit in which a fifth inductor L5, a third capacitor C3, and a resistance element R1 are connected in parallel.

  The first capacitor C1 and the resonance circuit 41 connected in series constitute a first series circuit having one end connected to the intermediate connection portion P1 and the other end grounded. Further, the second capacitor C2 and the resonance circuit 41 connected in series constitute a second series circuit in which one end is connected to the intermediate connection portion P2 and the other end is grounded. Thus, in the filter circuit 20, the resonance circuit 41 is shared by the first series circuit and the second series circuit.

  Next, the operation of the filter circuit 20 according to this embodiment will be described.

  First, the case where the common mode voltage Vi is applied to the input terminals 1A and 1B will be described. In this case, one end of the first inductor L1 (the end opposite to the intermediate connection portion P1) and the ground, and one end of the third inductor L3 (the opposite side to the intermediate connection portion P2). An equal voltage Vi is generated between the end of the terminal and the ground. The voltage Vi generated between one end of the first inductor L1 and the ground is divided by the first inductor L1 and the first series circuit (the first capacitor C1 and the resonance circuit 41), and the first A predetermined voltage is generated between both ends of the inductor L1 and between both ends of the first series circuit. Note that the arrow in the figure indicates that the potential ahead is higher. Similarly, the voltage Vi generated between one end of the third inductor L3 and the ground is divided by the third inductor L3 and the second series circuit (the second capacitor C2 and the resonance circuit 41). A predetermined voltage is generated between both ends of the third inductor L3 and between both ends of the second series circuit.

  Since the first inductor L1 and the second inductor L2 are electromagnetically coupled to each other, there is a predetermined amount between the both ends of the second inductor L2 according to the voltage generated between both ends of the first inductor L1. Voltage is generated. The voltage between the other end of the second inductor L2 (the end opposite to the intermediate connection portion P1) and the ground, that is, the voltage Vo between the terminal 2A and the ground is a voltage generated in the second inductor L2. Although expressed as the sum of the voltages generated in the first series circuit, these voltages cancel each other because they are in opposite directions, and as a result, are generated between one end of the first inductor L1 and the ground. That is, the voltage Vi generated between the terminal 1A and the ground. In this case, the first inductor L1 is constituted by the above-described coil 10, and a large impedance can be obtained over a wide band. When using a coil that does not provide sufficient impedance over a wide band as in the prior art, the voltage generated in the first series circuit increases as much as the impedance of the coil decreases, and as a result, The voltage Vo represented by the sum of the voltage generated in the first series circuit and the voltage generated in the second inductor L2 becomes large. In the present invention, a large impedance is ensured over a wide band. Since the obtained coil is used, such a problem can be avoided and the common mode noise can be sufficiently reduced.

  Similarly, since the third inductor L3 and the fourth inductor L4 are electromagnetically coupled to each other, according to the voltage generated between both ends of the third inductor L3, between the both ends of the fourth inductor L4. Generates a predetermined voltage. As a result, the voltage between the other end of the fourth inductor L4 (the end opposite to the intermediate connection portion P2) and the ground, that is, the voltage Vo between the terminal 2B and the ground is one of the third inductor L3. Is smaller than a voltage generated between the end of the terminal and the ground, that is, a voltage Vi generated between the terminal 1B and the ground. In this way, when the common mode voltage is applied to the input terminals 1A and 1B, the common mode voltage generated at the output terminals 2A and 2B is the common mode voltage applied to the input terminals 1A and 1B. Smaller than.

  In the filter circuit 20, even when a common mode voltage is applied to the output terminals 2A and 2B, the common mode voltage generated at the input terminals 1A and 1B is the same as the output terminal 2A. , 2B becomes smaller than the common mode voltage. As described above, according to this filter circuit, the common mode noise is applied to both the case where the common mode noise is applied to the input terminals 1A and 1B and the case where the common mode noise is applied to the output terminals 2A and 2B. Noise can be suppressed.

  According to this filter circuit 20, common mode noise can be effectively suppressed in a wide frequency range with a relatively simple configuration. In particular, since this filter circuit uses a coil having a large inductance in a predetermined high frequency band, common mode noise can be more effectively suppressed. Further, by providing a parallel circuit including the fifth inductor L5 and the third capacitor C3 as the resonance circuit 41, for example, a resonance is generated in the vicinity of the resonance point between the fifth inductor L5 and the third capacitor C3. As compared with the case where the circuit 41 is only the fifth inductor L5, the common mode noise component is more effectively suppressed. Therefore, by setting the resonance point of the parallel circuit to, for example, a desired high frequency band, it is possible to more effectively suppress noise components particularly in the high frequency band.

  FIG. 4 is a schematic perspective view showing the structure of a coil according to another preferred embodiment of the present invention. FIG. 5 is a schematic exploded perspective view of the coil shown in FIG. 4 and shows a state before winding.

  As shown in FIG. 4, the coil 50 includes a first ferrite core 11, a second ferrite core 12, and coil lead wires 13 </ b> A wound integrally with the ferrite cores 11 and 12. 13B. In the present embodiment, the first ferrite core 11 and the second ferrite core 12 are overlapped in the radial direction, the first ferrite core 11 is radially inward, and the second ferrite core 12 is radially outward. Is different from the coil 10 according to the above embodiment. It is preferable that the first ferrite core 11 is disposed radially inward of the second ferrite core 12. In general, the size of the coil inductance L is inversely proportional to the magnetic path length of the coil. Therefore, by reducing the diameter of the first ferrite core 11, the coil conductors 13A and 13B are wound around the first ferrite core 11. The magnetic path length of the rotated portion can be shortened, a large inductance value obtained due to the characteristics of the first ferrite core 11 can be sufficiently secured, and the resulting impedance value is also sufficient. Can be secured.

  In the present embodiment, the thickness T1 of the first ferrite core 11 is set equal to the thickness T2 of the second ferrite core 12 in the axial direction. Further, the outer diameter φ11 of the first ferrite core 11 is set equal to the inner diameter φ22 of the second ferrite core 12. Thereby, the two ferrite cores 11 and 12 can be overlapped in the radial direction. The material of these ferrite cores is the same as that of the coil 10 according to the above-described embodiment. The first ferrite core 11 is made of a MnZn-based ferrite material, and the second ferrite core 12 is made of a NiZn-based ferrite material.

  Similarly to the coil 10 described above, the coil 50 configured as described above is configured by a combination of a MnZn-based ferrite core and a NiZn-based ferrite core having different frequency characteristics, and therefore, in a high frequency band of 150 kHz to 30 MHz. When the impedance value is large and this is used for a filter, high frequency noise can be sufficiently reduced. In this embodiment, since a ferrite material is used, since the resistivity is higher than in the case of using an iron-based high permeability magnetic material as in the prior art, sufficient insulation can be ensured. . Furthermore, since the second core made of a NiZn-based ferrite material having a high resistivity is arranged on the outside as in the present embodiment, when the coil 50 is arranged on the substrate, it is between the other components and patterns. Sufficient insulation can be ensured.

  The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the invention described in the claims, and these are also included in the scope of the present invention. Needless to say.

  For example, although the case where the coil 10 was applied as a coil of a filter circuit was demonstrated in the said embodiment, it cannot be overemphasized that the coil 50 may be applied. Further, the filter circuit 20 shown in FIG. 3 has been described as an example of the filter circuit in which the coil 10 and the coil 50 are used. However, the filter circuit 20 is not limited to this and can be applied to various filter circuits.

(Example)
First, a first ferrite core and a second ferrite core were prepared. As the first ferrite core, an MnZn ferrite core (model number: HS72) manufactured by TDK Corporation was used. This ferrite core has an outer diameter φ11 = 12 mm, an inner diameter φ12 = 6 mm, and a thickness T1 = 3 mm. As the second ferrite core, a NiZn ferrite core (model number: HF70) manufactured by TDK Corporation was used. This ferrite core has an outer diameter φ21 = 10 mm, an inner diameter φ22 = 6 mm, and a thickness T2 = 3 mm. After the first and second ferrite cores are stacked in the axial direction, the enameled wire 13 having a diameter of 0.55 mm is wound on each of the four locations of the ferrite core by 6 turns to complete the toroidal coil as shown in FIG. It was. The four coils L1 to L4 of this toroidal coil correspond to the first to fourth inductors L1 to L4 of the filter circuit 20 shown in FIG.

  Among the toroidal coils having the above-described structure, the frequency characteristics of the inductance Ls [H] and the impedance Z [Ω] at one place of the winding part were measured.

  FIG. 7 is a graph illustrating measurement results of frequency characteristics of inductance and impedance of the coil according to the example. Here, the horizontal axis of the graph represents the frequency f [Hz], the left vertical axis represents the impedance Z [Ω], and the right vertical axis represents the inductance Ls [H].

  As shown in FIG. 7, the coil according to the example has a relatively high inductance of about 450 μH at a low frequency of 100 kHz, for example, and it was confirmed that an inductance of 10 μH or more was secured up to 4 MHz. As for impedance, there are two impedance peaks, and it was confirmed that a high impedance of 2 kΩ or higher was secured in a wide band from 1 MHz to 40 MHz. Further, if the impedance is 400Ω or more, it can be secured in a frequency band of 150 kHz or more.

(Comparative Example 1)
First, a first ferrite core was prepared. As the first ferrite core, a MnZn ferrite core (model number: HS72) manufactured by TDK Corporation was used. A toroidal coil as shown in FIG. 6 was completed by winding enamel wire 13 having a diameter of 0.55 mm on each of the four locations of the ferrite core for 6 turns.

  Among the toroidal coils having the above-described structure, the frequency characteristics of the inductance Ls [H] and the impedance Z [Ω] at one place of the winding part were measured.

  FIG. 8 is a graph showing measurement results of frequency characteristics of the inductance Ls [H] and impedance Z [Ω] of the coil according to Comparative Example 1.

  As shown in FIG. 8, the coil according to Comparative Example 1 has a relatively high inductance of about 450 μH at a low frequency of 100 kHz, for example, but it can be confirmed that an inductance of 10 μH or more can be secured only up to about 3 MHz. It was. As for the impedance, there is only one impedance peak, and high impedance of 2 kΩ or more is ensured in a narrow band from 1.5 MHz to 5 MHz.

(Comparative Example 2)
First, a second ferrite core was prepared. A NiZn ferrite core (model number: HF70) manufactured by TDK Corporation was used as the second ferrite core. The enameled wire 13 having a diameter of 0.55 mm was wound around each of the four locations of the ferrite core by 6 turns. Thus, a toroidal coil as shown in FIG. 6 was completed.

  Among the toroidal coils having the above-described structure, the frequency characteristics of the inductance Ls [H] and the impedance Z [Ω] at one place of the winding part were measured.

  FIG. 9 is a graph showing measurement results of frequency characteristics of the inductance Ls [H] and impedance Z [Ω] of the coil according to Comparative Example 2.

  As shown in FIG. 9, in the coil according to Comparative Example 2, only a relatively low inductance of about 70 μH was obtained even at a low frequency of 100 kHz, for example, and a relatively low inductance was obtained even in the entire band. As for the impedance, there is only one impedance peak, and a high impedance of 2 kΩ or higher is ensured only in a high frequency band of 20 MHz or higher.

  From the above results, it was found that the coil according to the example had a relatively high impedance in a high frequency band from 150 k to 30 MHz. This means that when this coil is applied to, for example, the above-described filter circuit, the attenuation amount of the noise component is increased, and the high-frequency noise can be sufficiently reduced.

FIG. 1 is a schematic perspective view showing the structure of a coil according to a preferred embodiment of the present invention. FIG. 2 is a schematic exploded perspective view of the coil shown in FIG. 1 and shows a state before winding. FIG. 3 is a block diagram showing a configuration of a filter circuit according to a preferred embodiment of the present invention. FIG. 4 is a schematic perspective view showing the structure of a coil according to another preferred embodiment of the present invention. FIG. 5 is a schematic exploded perspective view of the coil shown in FIG. 4 and shows a state before winding. FIG. 6 is a plan view schematically showing the structure of the toroidal coil according to the example and the comparative example. FIG. 7 is a graph illustrating measurement results of frequency characteristics of inductance and impedance of the coil according to the example. FIG. 8 is a graph showing measurement results of frequency characteristics of the inductance Ls [H] and impedance Z [Ω] of the coil according to Comparative Example 1. FIG. 9 is a graph showing measurement results of frequency characteristics of the inductance Ls [H] and impedance Z [Ω] of the coil according to Comparative Example 2.

Explanation of symbols

1A, 1B A pair of input terminals 2A, 2B A pair of output terminals 10 Coil 11 First ferrite core 12 Second ferrite core 13A, 13B Coil conductors for coils 14, 15 Core combination 20 Filter circuit 31 Winding by coil conductor 13A Wire 32 Winding 31a, 31b by coil conductor 13A Winding portion 32a, 32b Winding portion 41 Resonant circuit C1 First capacitor C2 Second capacitor C3 Third capacitor L1 First inductor L2 Second inductor L3 3rd inductor L4 4th inductor L5 5th inductor R1 1st resistance element P1 Intermediate connection part P2 Intermediate connection part φ11 Outer diameter of first ferrite core φ12 Inner diameter of first ferrite core φ21 Second ferrite Core outer diameter φ22 Inner diameter of the second ferrite core

Claims (6)

A first ferrite core; a second ferrite core superimposed on the first ferrite core; and a coil conductor wound integrally with the first and second ferrite cores. ,
The coil characterized in that the permeability attenuation range of the second ferrite core exists on the higher frequency side than the permeability attenuation range of the first ferrite core.   The coil according to claim 1, wherein the first ferrite core is made of a MnZn-based material, and the second ferrite core is made of a NiZn-based material.   The first ferrite core and the second ferrite core are overlapped in the axial direction, and the axial thickness of the first ferrite core is thicker than the axial thickness of the second core. The coil according to claim 1 or 2, characterized in that   The first ferrite core and the second ferrite core are overlapped in the radial direction, and the first ferrite core is disposed on the inner side in the inner diameter direction of the second ferrite core. The coil according to claim 1 or 2.   A filter circuit comprising the coil according to any one of claims 1 to 4. A filter circuit for reducing common mode noise propagating in the same phase through the first and second conductive lines,
First and second inductors inserted in series in the first conductive line and electromagnetically coupled to each other;
Third and fourth inductors inserted in series in the second conductive line and electromagnetically coupled to each other;
A first capacitor having one end connected to a connection point of the first and second inductors;
A second capacitor having one end connected to a connection point of the third and fourth inductors;
A resonance circuit inserted between the other end of each of the first and second capacitors and a ground line;
The filter circuit according to any one of claims 1 to 4, wherein the first to fourth inductors are configured using the coil according to any one of claims 1 to 4.

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