GB2250392A

GB2250392A - An LC composite element noise filter

Info

Publication number: GB2250392A
Application number: GB9120410A
Authority: GB
Inventors: Akira Naitou
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1990-11-29
Filing date: 1991-09-19
Publication date: 1992-06-03
Also published as: DE4133352A1; JPH04199502A; GB9120410D0; DE4133352C2

Abstract

An LC composite element has metal foils and insulative films 3, 4a, 4b which are alternately laminated and coiled thereby forming equivalent coils and condensers. There are at least two main metal foils 1, 5, and a plurality of earthed metal foils 2a, 2b which are interposed between the main metal foils and divided in plural numbers thereof, thereby forming X-condensers CX between the main metal foils for removing normal mode noise, and forming Y-condensers CY between the earthed metal foils and the main metal foils for removing common mode noise. <IMAGE>

Description

i- 22303?2 AN LC COMPOSITE ELEMENT This invention relates to an LC

composite element for use of a noise filter, and particularly to an LC composite element which can remove a common mode noise.

Generally speaking, in an electric magnetic environment device called "EMC (Electro Magnetic Compatibility) device", such as a power source, an LC noise filter is utilized for removing an alternative current noise.

Figure 6 is a circuit diagram showing generally an LC noise filter using a plurality of condensers (X-condenser and Y- condenser) as well as a plurality of coils. In Figure 6, numerals 11 through 13 designate, for instance, terminals for a receiving circuit, 21 through 23, for instance, terminals for a noise generating circuit. Among these terminals, the terminals 12 and 21 are, for instance, ground terminals.

CY11 and CY12 are condensers for removing the common mode noise, installed in series on the receiving circuit side, that is, Y-condenser. The Y-condenser CY11 is 1 inserted between the terminals 11 and 12, whereas the Ycondenser CY12 'S inserted between the terminals 12 and 13.

CY21 and CY22 are condensers (Y-condensers) for removing the common mode noise installed in series on the noise generating circuit. The Ycondenser CY21 'S inserted between the terminals 21 and 22, whereas the Ycondenser CY22 is inserted between the terminals 22 and 23.

CXj is a condenser for removing a normal mode noise installed on the receiving circuit side, that is, an X condenser, which is inserted between the terminals 11 and 13. CX2 is a condenser, an X-condenser, for removing a normal mode noise installed on the noise generating circuit side which is inserted between the terminals 21 and 23. L, is a coil inserted between the terminal 11 and 22, and L2 is a coil inserted between the terminals 13 and 23.

Next, explanation will be given to the operation of the conventional LC noise filter shown in Figure 6.

When an alternative current noise having a frequency f is generated at the noise generating circuit, and the noise signal is applied to terminals 21 and 23, a plurality of paths are formed which pass through the condensers CY11. CY12 and CX2, as well as the coils L, and L2. in the LC noise filter, and all of the noise signals including the normal mode noise and the common mode noise, are bypassed. Therefore these noise signals are not superposed at the terminals 11 and 13 on the receiving circuit side.

That is, the normal mode noise is removed by the path which passes through the terminal 21, X-condenser CX2 and the terminal 23. The common mode noise is removed by the path which passes through the terminal 21, the coil L,. the Y-condenser CY11 and the terminal 12, as well as by the path which passes through the terminal 23. the coil L2. the Y-condenser CY12 and the terminal 12.

In this case, the X-condenser W1, the Y-condensers CY21 and CY22 are provided in the circuit, so that noise signals from the terminals 11 and 13 can be removed, thereby eliminating the directionality thereof. and 15 enlarging the noise removal ratio thereof.

However, normally, the lead terminals accompanied by condensers and coils, contains the respective equivalent inductance and capacitance. Therefore it is difficult to take a complete impedance matching between the noise 20 filter and a device for filtration.

Accordingly, in the noise filter, a reflection of noise signal by the mismatching takes place. For instance, as shown in Figure 7, the impedance characteristic with respect to frequency f partially has resonance points and semiresonace point P, to P3. and the attenuation quantity of the noise signal has variation peaks.

Therefore, as shown in Japanese Unexamined Patent Publication No. 139619/1984, a structure is proposed in which a film-like LC composite element is utilized to thereby eliminate the generation of the resonance points. However, in the above publication, the LC composite element is of a dual layer structure. Therefore it is not possible to form a Ycondenser, and the removal of the common mode noise becomes impossible.

Since a conventional LC noise filter utilizes a plurality of coils and condensers as stated above, the impedance matching becomes difficult due to the structure of the lead terminals. Therefore, with respect to frequency f, a part of the impedance characteristic has a resonance point and a semiresonance point, and it can not generally be used. Furthermore, an LC composite element is proposed in which the lead terminal structure is eliminated. However, in this element, it is not considered to remove the common mode noise. Therefore it is not possible for the element to improve the noise removal ratio.

It is an object of the present invention to provide an LC composite element which enables to remove the common mode noise and improve the noise removal ratio.

According to an aspect of the present invention, there is provided an LC composite element having, metal foils and insulative films which are alternatively laminated and coiled thereby forming equivalent coils and condensers; characterized by having at least a couple of main metal foils; and a plurality of earthed metal foils which are interposed b6tween the couple of main metal foils and divided in plural numbers thereof, thereby forming an X-condenser, between the respective main metal foils for removing a normal mode noise, and thereby forming a Y-condenser, between the respective earthed metal foils and the respective main metal foils for removing a common mode noise.

Figure 1 is an exploded perspective showing an embodiment according to the present invention; Figure 2 is a perspective showing the set-up state of Figure 1; Figure 3 is a sectional view showing a layer structure of metal foils and insulative film in Figure 1; Figure 4 is an equivalent circuit diagram of Figure 1; Figure 5 is a characteristic diagram showing the relationship between the noise attenuation quantity and the frequency of an embodiment according to the present invention; Figure 6 is a circuit diagram showing a conventional LC noise filter; and Figure 7 is a characteristic diagram showing the relationship between the noise attenuation quantity and the frequency of the LC noise filter shown in Figure 6.

Explanation will be given to an embodiment of the 4 6 - present invention referring to drawings. Figure 1 is an exploded perspective view showing an embodiment of the present invention. Figure 2 is a perspective view showing the set-up state of Figure 1. Reference numerals 11 through 13 and 21 through 23 designate the same parts mentioned before. Figure 3 is a sectional view showing a layer structure of metal foils and insulative films in Figure 1.

In the drawings, a reference numeral 1 designates a main metal foil, 2a and 2b, divided and separeted earthed metal foils, 3, an insulative film inserted between the main metal foils 1 and the earthed metal foils 2a and 2b, 4a and 4b, insulative films which are divided and separated each other and oppose the back surfaces of the earthed metal foils 2a and 2b, 5, another main metal foil disposed opposing the main metal foil 1, through the insulative film 3, the earthed metal foils 2a and 2b, the insulative films 4a and 4b, and 6, an insulative film disposed opposing the back surface of the main metal foil 5.

A reference numeral 7 designates a cylindrical bobbin around which the main metal foil 1 through the insulative film 6 are coiled, 8, a bar-like magnetic core which is inserted through the central hollow part of the bobbin 7, and 9, a U-shaped magnetic core which is connected to the magnetic core 8, if necessary.

Figure 4 is a circuit diagram showing an equivalent circuit.of an embodiment of the present invention. The coils L, and L2 are formed by coiling around the bobbin 7. X-condensers CX, and CX2 are formed between the main metal foils 1 and 5 through the insulative film 3. The Y-condenser CY11 is formed between the main metal foil 1 and the earthed metal foil 2a through the insulative film 3. The Y-condenser CY:L2 is f ormed between the earthed metal foil 2a and the main metal foil 5 through the insulative f ilm 4a. The Y-condenser CY21 is formed between the main metal foil 1 and the earthed metal foil 2b through the insulative film 3. The Y-condenser CY22 is formed between the earthed metal foil 2b and the main metal foil 5 through the insulative film 4b.

Next, explanation will be given to the operation of an embodiment of the present invention shown in Figures 1 to 4, referring to Figure 5 which shows the frequency characteristic of the noise attenuation quantity.

In this case, the normal mode noise and the common mode noise are respectively removed as in the above, through the equivalently formed X-condenser CX2, and Ycondensers CY11 and CY12' On this occasion, the equivalently formed coils and condensers are regarded as gathering bodies of substantially small coils and condensers, which have inductances and capacitances by the distributed constant circuit. Accordingly, as shown in Figure 5, the circuit has no resonance points nor semiresonance points in the - 8 frequency characteristic of the noise attenuation quantity, and can improve the noise removal ratio compared with the conventional frequency characteristic (broken line).

As mentioned above, by equivalently forming a plurality of the Y-condensers CY11 and CY12, as well as CY21 and CY22 by using a divided plurity of earthed metal coils 2a and 2b, the impedance matching of the circuit with the object instruments, is promoted, the noise removal ratio of the common mode noise is improved, the directionality is eliminated, since a structure of the equivalent circuit is symmetrical, and the noise signals in the two directions can be removed.

Furthermore, in the above embodiment, the respective metal foils 1, 2a, 2b and 5 compose a single layer structure. However it is possible to enhance a capacity by forming a multi-layer structure in which the respective metal foils are multiplied.

Furthermore, the respective metal foils 1, 2a, 2b, 3 and 5 constitute a planar construction. However, it is possible to enlarge the capacity by enlarging substantially the surface area thereof by making the surface a rugged surface structure.

Furthermore, in this embodiment, the earthed metal foils 2a and 2b which form equivalent Y-condensers, are provided, one for the noise generating circuit and one for the receiving circuit side respectively. However it 9 - is possible to provide them at two places or more than two places by dividing them further. In this case, when the noise frequency as a target to eliminate is divided into a plurality of zones, the respective Ycondensers corresponding to the respective frequency zones, can be formed by which the noise removal ratio can further be improved. - As mentioned above, according to the present invention, at least a couple of main metal coils, and the earthed metal foils which are interposed between the main metal foils and divided into a plurality thereof, are provided, by which the X-condenser for removing the normal mode noise is formed between the respective main metal foils, and the Y-condenser for removing the common mode noise is formed between the drespective earthed metal foils and respective main metal foil. By the plurality of earthed metal foils, the directionality as a filter is eliminated and an LC composite element is obtained in which the noise removal ratio of the common mode noise is improved since a plurality of Y-condenser structure is equivalently formed between the respective earthed metal foils and the respective main metal foils.

Claims

1. An LC composite element having, metal foils and insulative films which are alternately laminated and coiled thereby forming equivalent coils and condensers; characterized by having at least two main metal foils; and a plurality of earthed metal foils which are interposed between the main metal foils and divided in plural numbers thereof, thereby forming an Xcondenser between the respective main metal foils for removing normal mode noise, and forming a Y-condenser between the respective earthed metal foils and the respective main metal foils for removing common mode noise.

2. An LC composite element substantially as herein described with reference to Figures 1 to 5 of the accompanying drawings.

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