JP2011019004A - Filter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter circuit for improving EMC at an inexpensive manufacturing cost.SOLUTION: In the filter circuit 1, a first chip inductor 3 and a second chip inductor 4, which are formed to have the same structure, are arranged on the mounting surface 2a of a wiring board 2. The first chip inductor 3 and the winding axis 4a of the second chip inductor 4 are parallel to each other and also are parallel to the mounting surface 2a of the wiring board 2. Terminals 3r, 4r, on the same direction sides of the first and second chip inductors 3, 4 are connected to each other.

Description

  The present invention relates to a filter circuit, and more particularly to a filter circuit that can be suitably used for a low-pass filter having a coil.

  In the conventional filter circuit 101, as shown in FIG. 6, a coil 103c used for a chip inductor is disposed. Since many electronic components that generate noise are mounted in the vicinity of the filter circuit 101, an unnecessary induced current I is generated from the coil 103c of the filter circuit 101 due to a change in magnetic flux generated in the filter circuit 101 due to the noise. It often happens.

  Therefore, in the conventional filter circuit, for example, the following two methods have been adopted as a method for improving the EMC (Electro-Magnetic Compatibility) by suppressing the influence of noise.

  As a first method, as shown in FIG. 7, two coils 104A and 104B whose winding directions are opposite to each other in the conventional filter circuit 101A are connected in series, and are generated in the respective coils 104A and 104B. This is a method of canceling the induced current I by arranging the induced current I in the opposite direction (the state of magnetic flux change is indicated by an arrow 10) (see Patent Document 1).

  As a second method, as shown in FIG. 8, in the conventional filter circuit 101B, two coils whose winding start directions (point P indicates the winding start direction) are opposite to each other. In this method, 105A and 105B are paired and connected in series (see Patent Document 2).

JP-A-4-159807 JP 2002-330035 A

  However, the conventional filter circuits 101A and 101B that employ the above-described method for suppressing the influence of noise have the following problems related to manufacturing cost and performance.

  That is, in the case of the conventional filter circuit 101A that employs the first method, as shown in FIG. 7, two types of coils 104A and 104B having opposite winding directions are required. Coil 104B (or 104A) must be prepared. For this reason, the number of parts in stock for the conventional filter circuit 101A increases, which increases the manufacturing cost of the filter circuit 101A.

  Further, in the case of the conventional filter circuit 101B employing the second method, as shown in FIG. 8, polar coils 105A and 105B must be prepared in order to determine the start of coil winding. Further, an expensive chip mounter must be used to control the mounting direction of the two coils 105A and 105B having polarity built in the chip inductor cases 105Ac and 105Bc mounted on the filter circuit 101B. As a result, there is a problem that the manufacturing cost of the conventional filter circuit 101B increases. Further, when the two coils 105A and 105B are arranged with the winding axis orthogonal to the mounting surface 102a of the wiring board 102, the length of the wiring 107 between the two coils 105A and 105B is the chip inductor case 105Ac. , 105Bc is longer by the length of the wiring 107a, 107b other than the coil, and there is a performance problem that unnecessary noise enters from the wiring 107.

  Therefore, the present invention has been made in view of these points, and an object of the present invention is to provide a filter circuit capable of improving EMC at a low manufacturing cost.

  In order to achieve the above-described object, the filter circuit of the present invention has, as a first aspect thereof, a wiring board having a mounting surface on which circuit elements are mounted and a winding axis parallel to the mounting surface of the wiring board. The first chip inductor disposed on the mounting surface of the wiring board is the same structure as the first chip inductor and the winding axis thereof is parallel to the winding axis of the first chip inductor. And a second chip inductor disposed on the mounting surface of the wiring board so that the winding direction is the same as the winding direction of the first chip inductor, and the first chip inductor and The terminals on the same direction side of the second chip inductor are connected to each other.

  According to the filter circuit of the first aspect of the present invention, the two chip inductors having the same structure are arranged so that their winding axes are parallel to the mounting surface of the wiring board. The induced current generated by the two chip inductors can be canceled without worrying about the winding start direction. Also, since two chip inductors are arranged with the winding axis parallel to the mounting surface of the wiring board, compared with the case where two coils are arranged with the winding axis orthogonal to the mounting surface of the wiring board. Thus, the wiring between the two chip inductors is shortened, and unnecessary noise can be prevented from entering from the wiring.

  The filter circuit according to the second aspect of the present invention is the filter circuit according to the first aspect, wherein one end of the filter circuit is connected in parallel to the series circuit in the subsequent stage of the series circuit including the first chip inductor and the second chip inductor. And a capacitor having the other end grounded.

  According to the filter circuit of the second aspect of the present invention, a low-pass filter can be formed by two chip inductors and a subsequent capacitor. In a low-pass filter through which a low-frequency signal flows, since an inductance of a coil built in the chip inductor is large, an unnecessary induced electromotive force is likely to be generated due to a change in an external magnetic field. That is, when the filter circuit of the present invention is used as a low-pass filter, it is possible to more effectively suppress the adverse effects of noise due to changes in the external magnetic field.

  A filter circuit according to a third aspect of the present invention is the filter circuit according to the first or second aspect, wherein the first chip inductor and the second chip inductor are arranged adjacent to each other in terms of magnetic flux change. It is said.

  According to the filter circuit of the third aspect of the present invention, the change in magnetic flux in the chip inductor becomes closer to the same as the arrangement interval between the two chip inductors is closer, so that the induction current can be canceled more effectively.

  According to the filter circuit of the present invention, it is possible to dispose a chip inductor without worrying about the mounting direction and the winding start direction of the two chip inductors, and unnecessary noise from the wiring between the two chip inductors. As a result, the EMC can be improved at a low manufacturing cost.

The perspective view which shows one Embodiment of the filter circuit of this invention Equivalent circuit diagram showing the filter circuit of this embodiment The graph which shows EMC of the filter circuit of this embodiment The perspective view which shows other embodiment of the filter circuit of this invention Equivalent circuit diagram showing filter circuit of other embodiment Equivalent circuit diagram showing a conventional filter circuit that exists in the past Equivalent circuit diagram showing an example when the first method is adopted in a conventional filter circuit Equivalent circuit diagram showing an example when the second method is adopted in a conventional filter circuit

  Hereinafter, the filter circuit of the present invention will be described with reference to an embodiment thereof.

  As shown in FIGS. 1 and 2, the filter circuit 1 of this embodiment includes a wiring board 2 and two chip inductors 3 and 4. Further, the filter circuit 1 of the present embodiment preferably includes a capacitor 5.

  As shown in FIG. 1, the wiring board 2 has a mounting surface 2a. Circuit elements such as two chip inductors 3 and 4 and a capacitor 5 are mounted on the mounting surface 2a.

  As shown in FIG. 1, the first chip inductor 3 has a coil 3c therein. The first chip inductor 3 is disposed on the mounting surface 2 a of the wiring board 2 so that the winding shaft 3 a of the coil 3 c is parallel to the mounting surface 2 a of the wiring board 2.

  As shown in FIG. 1, the second chip inductor 4 has the same structure as that of the first chip inductor 3, and the same coil 4c as that of the coil 3c used for the first chip inductor 3 therein. have. The second chip inductor 4 is disposed on the mounting surface 2 a of the wiring board 2 so that the winding axis 4 a of the coil 4 c is parallel to the winding axis 3 a of the first chip inductor 3. Therefore, the second chip inductor 4 is mounted on the wiring board 2 so that the winding direction of the coil 4c is the same as the winding direction of the first chip inductor 3, as shown in FIGS. It will be arranged on the surface 2a.

  Furthermore, the terminals 3r and 4r on the same direction side (the right side in FIG. 1) in the first chip inductor 3 and the second chip inductor 4 are connected to each other as shown in FIG. As a result, as shown in FIG. 2, the induction current i generated from the two chip inductors 3 and 4 due to electromagnetic induction due to external noise is connected in series so that the traveling directions of the induced currents i are opposite to each other. Become.

  Here, as a method of connecting the first chip inductor 3 and the second chip inductor 4, in order to prevent intrusion of noise, as shown in FIGS. 1 and 2, the first chip inductor 3 and the second chip inductor 3 It is preferable that the terminals 3r and 4r on the same direction side of the chip inductor 4 are connected with a shortest distance by, for example, a U-shaped or linear wiring 7.

  In addition, the first chip inductor 3 and the second chip inductor 4 are equivalent or approximate to cause a magnetic flux change in terms of a magnetic flux change caused by external noise (the state of the magnetic flux change is indicated by an arrow 10). It is preferable that they are arranged adjacent to each other.

  Further, in the conventional circuit, when the inductance of one chip inductor to be replaced is L, the combined inductance of the two chip inductors 3 and 4 is matched with the inductance of the one chip inductor to be replaced. Each inductance of the first chip inductor 3 and the second chip inductor 4 is preferably set to L / 2.

  As shown in FIGS. 1 and 2, one end of the capacitor 5 is connected in parallel to the series circuit in the subsequent stage of the series circuit composed of the first chip inductor 3 and the second chip inductor 4, and the other end is connected to the other end. It is grounded by being connected to the ground 6.

  Next, the operation of the filter circuit 1 of the present embodiment will be described.

  In the filter circuit 1 of the present embodiment, as shown in FIG. 1, the first chip inductor 3 and the second chip inductor 4 formed in the same structure are disposed on the mounting surface 2 a of the wiring board 2. . The winding axes 4a of the first chip inductor 3 and the second chip inductor 4 are parallel to each other and are also parallel to the mounting surface 2a of the wiring board 2. Further, since the terminals 3r and 4r on the same direction side of the first chip inductor 3 and the second chip inductor 4 are connected to each other in a state of being placed on the mounting surface 2a of the wiring board 2, the first chip As shown in FIG. 2, the inductor 3 and the second chip inductor 4 are connected in series so that the traveling directions of the induced currents i generated from the two chip inductors 3 and 4 by electromagnetic induction are opposite to each other. Will be connected.

  Here, the conditions for canceling the induced electromotive force (inductive current i) generated by the two chip inductors 3 and 4 due to external noise are as follows: (1) Inductor 3 having coiled current paths (coils) 3c and 4c 4), (2) the winding shafts 3a and 4a of the two inductors 3 and 4 connected in series are arranged in parallel, and (3) the two inductors 3 and 4 connected in series are connected to the wiring board. In other words, the terminals 3r and 4r on the same direction in the state of being mounted on 2 are connected to each other. In the filter circuit 1 of the present embodiment, as shown in FIGS. 1 and 2, the axes of the coils of two inductors having the same structure are arranged in parallel in the same direction, and between them Since the wiring to be connected is connected to the terminals 3r and 4r on the same direction side of the two inductors, the above conditions (1) to (3) are satisfied. Therefore, the induced current i generated in the first chip inductor 3 and the second chip inductor 4 by the magnetic flux change 10 derived from the external noise can be canceled out.

  Further, since the winding axes 3 a and 4 a of the first chip inductor 3 and the second chip inductor 4 are arranged in parallel to the mounting surface 2 a of the wiring board 2, the chip is mounted on the mounting surface 2 a of the wiring board 2. Compared to the case of the conventional circuit in which the winding axes of the inductors are arranged orthogonally, the first chip inductors 3 and 4 are not concerned about the mounting direction and the winding start direction (see FIGS. 7 and 8). The induced current i generated by the chip inductor 3 and the second chip inductor 4 can be canceled out.

  Furthermore, since the winding axes 3a and 4a of the first chip inductor 3 and the second chip inductor 4 are arranged in parallel to the mounting surface 2a of the wiring board 2, they are arranged with respect to the mounting surface 2a of the wiring board 2. As compared with the case where two coils are arranged with the winding axes orthogonal to each other (see FIG. 8), the wiring 7 between the two chip inductors 3 and 4 is shortened. Specifically, as is apparent from a comparison between FIGS. 1 and 8, the length of the internal wiring other than the coil in the chip inductor in which the winding axis is orthogonal to the mounting surface 2a of the wiring board 2 can be shortened. As a result, it is possible to prevent unnecessary noise from entering from the wiring 7 between the two chip inductors 3 and 4.

  Further, as shown in FIG. 2, it is preferable that a capacitor 5 is connected in parallel at the subsequent stage of the series circuit including the first chip inductor 3 and the second chip inductor 4. Thus, a low-pass filter can be formed by the two chip inductors 3 and 4 and the capacitor 5 at the subsequent stage. In a low-pass filter through which a low-frequency signal flows, since an inductance of a coil built in the chip inductor is large, unnecessary induced electromotive force is likely to be generated due to a change in external magnetic field (change in magnetic flux). That is, when the filter circuit 1 of the present embodiment is used as a low-pass filter, it is possible to more effectively suppress the adverse effects of noise due to changes in the external magnetic field.

  Furthermore, as shown in FIGS. 1 and 2, the first chip inductor 3 and the second chip inductor 4 are preferably arranged adjacent to each other in terms of magnetic flux change. As the arrangement interval between the first chip inductor 3 and the second chip inductor 4 becomes closer, the change in magnetic flux in the chip inductor becomes closer to the same, so that the induced current i can be canceled more effectively.

  Based on the above operation and effect, FIG. 3 shows an EMC of the filter circuit 1 of the present embodiment. In the graph of FIG. 3, the filter circuit 1 of this embodiment in which the first chip inductor 3 and the second chip inductor 4 having a resonance peak at 150 kHz are mounted is disposed near the synthesizer disposed outside the filter circuit 1. It shows the degree of influence on the synthesizer when the frequency is continuously changed from 0 to 1000 kHz. In FIG. 3, the degree of influence when the filter circuit 1 of the present embodiment is used is indicated by a solid line. Further, a comparison target is a single chip inductor having the same inductance as the combined inductance of the first chip inductor 3 and the second chip inductor 4, instead of the first chip inductor 3 and the second chip inductor 4. A normal filter circuit (see FIG. 6), and the degree of influence is indicated by a dotted line.

  In the filter circuit 1 of the present embodiment, as shown in FIG. 3, it has been clarified that the spurious (unnecessary wave) is reduced by about 20 dBc in the vicinity of 150 kHz than the normal filter circuit to be compared. Further, it has been clarified that the filter circuit 1 of the present embodiment has a lower influence than the normal filter circuit to be compared over the entire measurement frequency. As a result, it was confirmed that the filter circuit 1 of the present embodiment was effective as a low-pass filter that attenuates the power system low frequency band.

  That is, according to the filter circuit 1 of the present embodiment, the chip inductor can be disposed without worrying about the mounting direction and the winding start direction of the two chip inductors 3, 4, and the two chip inductors 3. Since unnecessary noise is prevented from entering from the wiring 7 between the four, there is an effect that the EMC can be improved at a low manufacturing cost.

  In addition, this invention is not limited to embodiment mentioned above etc., A various change is possible as needed.

  For example, as shown in FIGS. 4 and 5, in the filter circuit 1A of another embodiment, the winding axis 3a of the first chip inductor 3 and the winding axis 3a of the first chip inductor 3 are preferably mounted on the wiring board 2 having the elongated mounting surface 2a. The winding axis 4a of the second chip inductor 4 may be arranged on a straight line. Also in this case, like the filter circuit 1 of the present embodiment shown in FIGS. 1 and 2, the winding shafts 3a and 4a satisfy the requirement that they are arranged in parallel to each other. It is obvious that the same operational effects as the operational effects in the embodiment can be obtained.

DESCRIPTION OF SYMBOLS 1, 1A filter circuit 2 Wiring board 2a Mounting surface 3 First chip inductor 3a Coil winding axis 3c Coil 4 Second chip inductor 4a Coil winding axis 4c Coil 5 Capacitor 6 Ground 7 Wiring i Inductive current

Claims (3)

A wiring board having a mounting surface on which circuit elements are mounted;
A first chip inductor disposed on the mounting surface of the wiring board such that a winding axis thereof is parallel to the mounting surface of the wiring board;
The winding structure is the same as that of the first chip inductor, the winding axis thereof is parallel to the winding axis of the first chip inductor, and the winding direction thereof is the same direction as the winding direction of the first chip inductor. And a second chip inductor disposed on the mounting surface of the wiring board so that
A filter circuit, wherein terminals on the same direction side of the first chip inductor and the second chip inductor are connected to each other. In the subsequent stage of the series circuit composed of the first chip inductor and the second chip inductor, a capacitor having one end connected in parallel to the series circuit and the other end grounded is provided. The filter circuit according to claim 1. 3. The filter circuit according to claim 1, wherein the first chip inductor and the second chip inductor are arranged adjacent to each other in terms of magnetic flux change.

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