JPH08162883A - Emi filter - Google Patents

Abstract

PURPOSE: To surely reduce a high frequency component in the EMI filter mounted on a printed circuit board for high frequency noise countermeasures so as to reduce the high frequency component in an electric signal. CONSTITUTION: An input lead wire prepared for reception of an electric signal and acting like an inductor, an output lead wire prepared for an output of an electric signal and acting like an inductor, a capacitor 200 provided to apply capacitive connection between ground and a connecting part of input output lead wires 9 form the EMI filter 100. The capacitor 200 is made up of a dielectric body 10 formed on an outer circumference of the lead connection part and an electrode 11 formed on the outer circumferential part of the dielectric body 10 to be soldered with ground.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EMI filter mounted on a printed wiring board as a countermeasure against high frequency noise to reduce the high frequency component of an electric signal, and more particularly to reliably reduce the high frequency component. It relates to an EMI filter.

In recent years, radio wave interference caused by electronic devices has become a serious problem, and it has become necessary to reduce high frequency noise generated by electronic devices. In order to reduce this high frequency noise, a high frequency cut filter called an EMI filter has been used. In order to make this EMI filter practical,
It is necessary to build a structure that can reliably reduce high-frequency components.

[0003]

2. Description of the Related Art An EMI filter, as shown in FIG.
It consists of two inductors connected in series and a capacitor inserted between the connection point of these inductors and the ground. By this structure, the high frequency component of the input electric signal is bypassed to the ground. As a result, the high frequency component of the electric signal is reduced and output.

FIG. 7 shows a conventional EM composed of three terminals.
3 illustrates an external view of an I filter. In the figure, 1 is a filter body in which an inductor and a capacitor are coated with resin, 2 is an input terminal, 3 is an output terminal, and 4 is a ground terminal.

As shown in FIG. 8, a dielectric 5 having electrodes 6 mounted on both surfaces is provided inside the filter body 1, and one of the electrodes 6 serves as an input terminal 2 and an output terminal 3. A capacitor is prepared by connecting the other electrode 6 to the lead forming the ground terminal 4 while being connected to the lead connecting the two, and the ferrite beads 7 are attached to the lead forming the input terminal 2. The inductor is prepared by being externally inserted, and the inductor is prepared by externally inserting the ferrite beads 7 to the leads forming the output terminal 3.

According to this structure, the conventional EMI filter of the three-terminal type realizes the circuit structure of FIG. 6 and bypasses the high frequency component of the input electric signal to the ground, thereby The high frequency component of the signal is reduced and then output.

[0007]

However, in such a conventional three-terminal type EMI filter, since the lead is taken out from the capacitor and connected to the ground, the high frequency component is generated by the inductance of the lead. There is a problem that it cannot be effectively reduced.

That is, in such a conventional three-terminal type EMI filter, as shown in FIG. 9, an inductance remains between the capacitor and the ground, and this residual inductance causes a resistance component to a high frequency. Therefore, there is a problem that the high frequency component of the input electric signal cannot be effectively bypassed to the ground, and the high frequency component of the electric signal cannot be effectively reduced. In particular, in a high frequency band exceeding 100 MHz, the influence of this residual inductance becomes extremely large.

Moreover, such a conventional three-terminal type EMI filter has a drawback that the resistance of the lead between the capacitor and the ground adversely affects the filter performance and prevents the reduction of high frequency components. .

On the other hand, an EMI filter having a chip structure having a relatively small residual inductance is also provided on the market. However, even with such an EMI filter having a chip structure, a residual pattern and a resistance are required because a pattern for drawing out from the ground layer is required. Is not completely eliminated, and the problem remains that high frequency components cannot be effectively reduced. Moreover, the chip-structured EMI filter can be used only for a surface-mounted printed wiring board, and the rated current cannot be increased.

Thus, according to the prior art, E
There is a problem that the effect of reducing the high frequency band of the MI filter is small. One way to deal with this is to increase the capacitance of the capacitor and the inductance of the inductor, but if this is done, the filtering effect will extend to the low frequency band. Then, there arises a new problem that a desired signal waveform cannot be obtained.

The present invention has been made in view of the above circumstances, and provides a new EMI filter capable of reliably reducing a high frequency component of an electric signal by eliminating a residual inductance and a resistance component. To aim.

[0013]

In order to achieve this object, according to the present invention, an input and an output lead connected in series with an inductance, and an input lead and an output lead inserted between the connection point of these two leads and the ground. In an EMI filter including a capacitor, the capacitor includes a dielectric formed on the outer circumference of the lead connection portion and an electrode formed on the outer circumference of the dielectric and capable of being soldered to the ground. It is characterized by being configured.

When adopting this structure, the lead connecting portion is formed in a U shape, and the input and output leads are bent so that they are oriented in the same direction as the U shape, and the lead connecting portion is formed. Is preferably connected to.

[0015]

In the EMI filter of the present invention, the capacitor portion constituting the EMI filter is inserted into, for example, a through hole that is in contact with the ground pattern of the printed wiring board, and the electrode and the through hole are soldered. Connect the capacitor directly to ground.

As described above, in the EMI filter of the present invention, since the capacitor forming the EMI filter can be directly connected to the ground without using any lead, the residual inductance and the resistance component can be eliminated. As a result, the high frequency component of the electric signal can be surely reduced.

[0017]

EXAMPLES The present invention will be described in detail below with reference to examples. FIG. 1 shows a three-terminal EMI constructed according to the present invention.
1 illustrates an example of a filter 100. Here, in the figure,
The same components as those described in FIG. 8 are designated by the same reference numerals.

In FIG. 1, the EMI filter 100 is
This EM is attached to the multilayer printed wiring board 8.
As shown in FIG. 1B, a cylindrical dielectric 10 covering the outer circumference of the lead 9 and an outer circumference of the dielectric 10 are provided in the middle of one lead 9 that constitutes the I filter 100. There is provided a capacitor 200 including a cylindrical electrode 11 covered with the capacitor. This capacitor 200 is
The electrodes 11 and the through holes 12 are inserted into the through holes 12 of the multilayer printed wiring board 8 and soldered there, so that they are connected to the ground pattern 13 of the multilayer printed wiring board 8.

If the capacitor 200 is composed of a monolithic ceramic capacitor, the capacitance of the capacitor can be made larger than the size thereof, which is advantageous in realizing miniaturization, and the error in the capacitance of the capacitor can be suppressed to be small. Become.

Both ends of the lead 9 are bent in a U-shape to form an S-shape as a whole, and one end of the lead 9 constitutes an input terminal 2 for inputting an electric signal to be filtered. Then, it is inserted into another through hole 14 of the multilayer printed wiring board 8 and then soldered to a predetermined pattern of the multilayer printed wiring board 8. On the other hand, the other end constitutes an output terminal 3 for outputting a filtered electric signal, and is inserted into another through hole 15 of the multilayer printed wiring board 8 where a predetermined pattern of the multilayer printed wiring board 8 is formed. To be soldered to.

Between the capacitor 200 and the output terminal 3, a ferrite bead 7 is externally inserted to provide an inductor constituting the EMI filter 100. On the other hand, between the capacitor 200 and the input terminal 2, the EMI is caused by the inductance of the lead 9 itself in this portion.
The inductors that make up the filter 100 are provided.

In order to allow the EMI filter 100 to be assembled, a flexible portion 16 that provides flexibility is prepared in the lead 9 portion between the capacitor 200 and the input terminal 2. Needless to say, the entire lead 9 may be made of a flexible material.

In the EMI filter 100 having such a structure, since the electrode 11 of the capacitor 200 which constitutes the EMI filter 100 is directly connected to the ground pattern 13 of the multilayer printed wiring board 8, the capacitor 200 It is possible to completely eliminate the lead between the ground pattern 13 and the ground pattern 13. From this, the residual inductance and the resistance component can be completely eliminated, the high frequency component can be surely reduced, and it is not necessary to increase the capacitance of the capacitor 200 more than necessary, and a desired signal waveform is obtained. Will be able to.

FIG. 2 shows another embodiment of the three-terminal type EMI filter 100 constructed according to the present invention. Figure 2
Also in the above, the EMI filter 100 is assembled to the multilayer printed wiring board 8.
The middle portion of one lead 9 forming 0 is bent in a U shape, and the U portion has a cylindrical shape coated on the outer circumference of the lead portion as shown in FIG. 2B. There is provided a capacitor 200 including a dielectric body 10 and a cylindrical electrode 11 that covers the dielectric body 10. The capacitor 200 is inserted into the through hole 12 of the multilayer printed wiring board 8, and the electrode 11 and the through hole 12 are soldered there to be connected to the ground pattern 13 of the multilayer printed wiring board 8.

If the capacitor 200 is composed of a monolithic ceramic capacitor, the capacitance of the capacitor can be increased as compared with its size, which is advantageous in realizing miniaturization, and the error in the capacitance of the capacitor can be kept small. Become.

Both ends of the lead 9 are connected to the capacitor 200.
Is bent in a U-shape in the same direction as the above, and one of its ends constitutes an input terminal 2 for inputting an electric signal to be filtered and is inserted into another through hole 14 of the multilayer printed wiring board 8. , There multilayer printed wiring board 8
Is soldered to a predetermined pattern. On the other hand, the other end constitutes an output terminal 3 for outputting a filtered electric signal, and is inserted into another through hole 15 of the multilayer printed wiring board 8 where a predetermined pattern of the multilayer printed wiring board 8 is formed. To be soldered to.

The ferrite beads 7 are externally inserted between the capacitor 200 and the input terminal 2 to provide an inductor which constitutes the EMI filter 100, and between the capacitor 200 and the output terminal 3. The ferrite beads 7 are externally attached to the EMI filter 1.
The inductors that make up 00 are provided.

In the EMI filter 100 having such a structure, the electrode 11 of the capacitor 200 forming the EMI filter 100 is directly connected to the ground pattern 13 of the multilayer printed wiring board 8, so that the capacitor 200 It is possible to completely eliminate the lead between the ground pattern 13 and the ground pattern 13. From this, the residual inductance and the resistance component can be completely eliminated, the high frequency component can be surely reduced, and it is not necessary to increase the capacitance of the capacitor 200 more than necessary, and a desired signal waveform is obtained. Will be able to.

According to the EMI filter 100 of this embodiment, the EMI filter 100 can be assembled to the multilayer printed wiring board 8 from one direction, which is extremely convenient for assembly. Note that, in FIG. 2B, the U-shaped portion of the dielectric 10 forming the capacitor 200 is independently formed between the U-shapes, so that the electrode 11 of the capacitor 200 has the dielectric material 10.
Although it is shown in the form of cutting, the dielectric 10 may be integrally formed between U-shapes and the electrode 11 may be formed on the outer periphery thereof as shown in FIG. It's good.

FIG. 4 shows another embodiment of the three-terminal type EMI filter 100 constructed according to the present invention. The difference between this embodiment and the embodiment of FIG. 2 is that the electrode 11 of the capacitor 200 is soldered to the ground pattern 13 of the multilayer printed wiring board 8 in the embodiment of FIG. Then, the electrode 11 is soldered to the case 17 in which the multilayer printed wiring board 8 is continuously provided. In order to realize the connection to the case 17, the lead 9 between the input terminal 2 and the capacitor 200 is provided with the flexible portion 18, and the lead 9 between the output terminal 3 and the capacitor 200 is flexible. The point is that the part 18 is provided. Also, without using the ferrite beads 7, the lead 9
By forming a part of the coil into a coil shape, the EMI filter 2
It is also different in that an inductor which constitutes 00 is provided.

By adopting such a configuration, the electrode 11 of the capacitor 200 is connected to the case 1 having a lower impedance.
It becomes possible to attach it to the earth ground of 7. It should be noted that if a configuration is adopted in which an inductor is provided by using a coil shape, magnetic saturation does not occur, which is suitable for a large current application.

FIG. 5 shows another embodiment of the three-terminal type EMI filter 100 constructed according to the present invention. This embodiment has a plurality of EMI filters 1 according to the embodiment of FIG.
00 is juxtaposed to expose the capacitor 200, the input terminal 2 and the output terminal 3, and they are integrally molded to form an integrated EMI filter 100.

When the EMI filter 100 having such a configuration is used, in order to reduce high frequency components such as bus lines,
The EMI filter 100 can be collectively mounted, and as a result, downsizing and cost reduction can be realized.

[0034]

As described above, in the EMI filter of the present invention, the capacitor constituting the EMI filter can be directly connected to the ground without using any lead, so that the residual inductance and the resistance component are eliminated. As a result, it is possible to reliably reduce the high frequency component of the electric signal, and it is not necessary to increase the capacitance of the capacitor more than necessary, so that a desired signal waveform can be obtained. Become.

[Brief description of drawings]

FIG. 1 is an embodiment of the present invention.

FIG. 2 is another embodiment of the present invention.

FIG. 3 is an explanatory diagram of a structure of a capacitor.

FIG. 4 is another embodiment of the present invention.

FIG. 5 is another embodiment of the present invention.

FIG. 6 is an equivalent circuit diagram of an EMI filter.

FIG. 7 is an external view of a three-terminal EMI filter.

FIG. 8 is an internal configuration diagram of an EMI filter.

FIG. 9 is an explanatory diagram of a residual inductance of the EMI filter.

[Explanation of symbols]

 1 Filter Main Body 2 Input Terminal 3 Output Terminal 4 Ground Terminal 8 Multilayer Printed Wiring Board 9 Lead 10 Dielectric 11 Electrode 12 Through Hole 100 EMI Filter 200 Capacitor

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H03H 7/01 Z 8321-5J

Claims (6)

[Claims] 1. An input lead prepared for inputting an electric signal and functioning as an inductor, an output lead prepared for outputting an electric signal and functioning as an inductor, a connecting portion of the input and output leads, and a ground. An EMI filter comprising a capacitor provided for capacitively connecting a capacitor, the capacitor being formed on the outer periphery of the lead connecting portion, and formed on the outer periphery of the dielectric, and being connected to a ground and a solder. An EMI filter characterized by being configured with electrodes that can be attached. 2. The EMI filter according to claim 1, wherein the lead connection portion is formed in a U shape, and the input and output leads are bent so that they are oriented in the same direction as the U shape. An EMI filter characterized in that it is configured to be connected to a section. 3. The EMI filter according to claim 1, wherein either or both of the lead connecting portion and the input lead and the lead connecting portion and the output lead are flexible. An EMI filter, characterized in that it is arranged to be connected. 4. An integrated EMI filter configured by arranging a plurality of EMI filters in parallel and molding the EMI filters, wherein each EMI filter is provided outside the mold that is prepared for inputting an electric signal and functions as an inductor. An input lead having an exposed portion, an output lead having an exposed portion outside the mold, which is prepared for outputting an electric signal and functions as an inductor, and which is provided to capacitively connect the connection portion of the input and output leads and the ground. And a capacitor having an exposed portion outside the mold, the lead connecting portion is formed in a U shape, and the input and output leads are bent so as to face the same direction as the U shape. And a dielectric formed on the outer periphery of the lead connecting portion, and the dielectric. An EMI filter, characterized in that it is formed on the outer periphery of a substrate and is composed of a ground and electrodes that can be soldered. 5. The EMI filter according to claim 1, 2, 3 or 4, wherein one or both of the input lead and the output lead are equipped with an inductance enhancing member for enhancing the inductance, or a coil for enhancing the inductance. An EMI filter having a shape. 6. The EM according to claim 1, 2, 3, 4 or 5.
In the I filter, the capacitor is formed of a laminated ceramic structure, which is an EMI filter.