JPH07201579A - Noise filter - Google Patents

Abstract

PURPOSE:To obtain an attenuation effect equal to or higher than one with a circular core against high-frequency noises, by arranging a signal line in the hollow part of a specific ferrite core. CONSTITUTION:The U-shaped ferrite core 10 of the noise filter has a U-shaped construction of a constant thickness. A ratio a/b is set to be 9 to 60, where (a) represents the distance from the bottom 12 of the U-shaped inside up to this free ends 14 and 16, and (b) represents the distance between both free ends 14 an 16. A signal line SL is arranged in the hollow part 18, at the bottom 12 for example. As a result, a bad influence against signals being in a relatively low-frequency band is made extremely small and made to pass, and it becomes possible to obtain an attenuation effect equal to or higher than one with a circular core against high-frequency noises.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention eliminates or suppresses noise generated inside an electric device or noise generated outside and flowing into an electronic device through a signal line by passing a signal line of an electronic device inside. Regarding noise filter.

[0002]

2. Description of the Related Art Conventionally, as a method of removing or suppressing noise flowing in a signal line, a technique is known in which a ferrite is fitted around the signal line and the noise flowing in the signal line is attenuated by the ferrite. In that case, for example, an undivided ferrite core or a split type ferrite core configured to form an annular closed magnetic circuit with only ferrite was used.

In these noise filters, a loop of the magnetic flux generated by the current flowing through the signal line is formed in the closed magnetic circuit formed of ferrite, so that the electric energy is converted into heat energy and attenuated. Therefore, the noise filter is generally configured to form a closed magnetic circuit only with ferrite. Therefore, particularly in the split type, many efforts have been made to magnetically couple the split surfaces of the ferrite. For example, various proposals have been made on how to bring the divided surfaces into close contact.

[0004]

However, in the conventional noise filter using the annular type ferrite core, a predetermined noise attenuation effect can be obtained by the closed magnetic path formed by the ferrite core, but at the same time, it is in the signal band. The impedance becomes large even in the low frequency band of several tens of MHz, which may adversely affect the signal flowing through the signal line. However, since the conventional ones mainly focus on noise removal, even if the consideration for the adverse effect on the signal is sacrificed, the one that forms the closed magnetic circuit only by ferrite, which has a high noise attenuation effect, is adopted. .

This time, the applicant of the present application also used a ferrite core in a state having a gap (gap), which has not been considered in the past, under a predetermined condition to form a closed magnetic circuit only with ferrite. It has been found that an impedance-frequency characteristic different from that of the configuration can be obtained. Furthermore, its impedance-frequency characteristics allow signals of a relatively low frequency band to pass without being attenuated, and for high-frequency noise, equal to or higher than those using an annular core. It has been found that a damping effect can be obtained.

Therefore, in the present invention, the above-mentioned adverse effects on the signals in the relatively low frequency band are passed as small as possible, and high frequency noise is equal to or more than that in the case of using the annular core. An object of the present invention is to provide a noise filter that can obtain an attenuation effect.

[0007]

In order to achieve such an object, the present invention has the following constitution as means for solving the problem. That is, the noise filter according to claim 1 is a ferrite core formed in a substantially U shape, the distance from the inner bottom portion to the free end is a, and the distance between both free ends is b, and their ratio is It is characterized in that a ferrite core having a / b of 9 to 60 is used and a signal line is arranged in a hollow portion of the ferrite core to attenuate noise flowing through the signal line.

The noise filter according to claim 2 is
The ferrite core is formed in a substantially C shape, and the distance on the average magnetic path between both free ends thereof is 1 to 25 of the average magnetic path length.
%, And a signal line is arranged in the hollow portion of the ferrite core to attenuate noise flowing through the signal line.

[0009]

As described above, the ferrite core in the state of having a gap has a different impedance from that of the conventional structure without a gap in which a closed magnetic circuit is formed only by ferrite when used under predetermined conditions described later.
The frequency characteristic can be obtained, and the impedance-frequency characteristic allows the signal having a relatively low frequency band to be passed with a minimum adverse effect, and with respect to high frequency noise, it is equal to or higher than that of the annular core. It was found that a damping effect can be obtained.

Then, as the predetermined condition, as shown in the above claims 1 and 2, a case where a substantially U-shaped ferrite core is used and a case where a substantially C-shaped ferrite core is used are proposed. . First, when the substantially U-shaped ferrite core according to claim 1 is used, a ratio of the distance a from the inner bottom to the free ends and the distance between the free ends to b is a / b. 9 to 60, when the signal line is arranged in the hollow part of the ferrite core, the signal flowing through the signal line in the relatively low frequency band is passed through with a small attenuation degree, For high-frequency noise, a damping effect equal to or higher than that of a closed magnetic circuit can be obtained.

Within the above range of the ratio a / b (9 to 60), the impedance decreases as the ratio a / b decreases, but even if the ratio a / b is about 9, it is high. Since the impedance in the frequency band can be obtained up to about 80% of that in the case without a gap, the ratio a / b can be lowered in order to lower the impedance in the low frequency band to further reduce the adverse effect on the signal flowing through the signal line. It is desirable to set to. It was also confirmed that when the ratio a / b increases to around 24, the impedance becomes higher in the high frequency band than in the case of the ring-shaped core without gap. Therefore, when the ratio a / b is 24 or more, the characteristics of low impedance in the low frequency band and high impedance in the high frequency band can be better obtained. However, when the ratio a / b is about 60, the difficulty in manufacturing increases, so a range up to that level is proposed.

On the other hand, when the substantially C-shaped ferrite core according to claim 2 is used, the distance on the average magnetic path between the free ends (that is, the magnetic path gap) is determined by the average magnetic path length. 1 to 25%, as in the case of using the substantially U-shaped ferrite core, the degree of attenuation is small with respect to the signal flowing through the signal line in the relatively low frequency band and the adverse effect is minimized. It is made small and passed, and for high-frequency noise, an attenuation effect equivalent to or more than that of an annular core having no C-shaped notch, that is, a ring-shaped core can be obtained.

In this case, if the ratio of the magnetic path gap to the average magnetic path length is within the range, the impedance at about several tens of MHz is obtained especially when there is no magnetic path gap (that is, the ring-shaped ferrite core). The decrease is significant. Therefore, it is very effective from the viewpoint of preventing an adverse effect on the signal flowing through the signal line. Also, the above 1 to 25
In the range of the ratio of the magnetic path gap to the average magnetic path length of%, the larger the ratio, the lower the impedance as a whole, but even if the ratio is about 25%, in the high frequency band (for example, 100 MHz or more). Since the impedance can be obtained up to about 80% of the case without a gap, the ratio a / b is set to be low when it is desired to further lower the impedance in the low frequency band and further reduce the adverse effect on the signal flowing through the signal line. Is desirable. It was also confirmed that when the ratio is reduced to about 4%, the impedance becomes higher in the high frequency band of 100 MHz or more than in the case without the gap. When the ratio falls below 4%, the characteristics become even better.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings. [First Embodiment] FIG. 1A is a perspective view showing a U-type ferrite core 10 used in a noise filter according to the first embodiment of the present invention, and FIG. The U-shaped ferrite core 10 has a constant thickness and is formed in a U shape.
Assuming that the distance from the bottom portion 12 inside the letter "a" to the free ends 14 and 16 is "a" and the distance between both free ends 14 and 16 is "b", the ratio (a / b) is 1 to 24. It is set. Then, the signal line SL is arranged in the hollow portion 18, that is, the bottom portion 12 in this embodiment.

FIG. 3 shows the results of studying the relationship between the ratio (a / b) and the impedance-frequency characteristics in this U-type ferrite core 10. The core used in this experiment is a =
7 to 19 mm and b = 0.8 mm. In FIG. 3, a /
When b = 24 (a = 19 mm, b = 0.8 mm) and a
/ B = 9 ((a = 7 mm, b = 0.8 mm), and the case of an annular core for comparison is indicated by a broken line. Note that the U-type ferrite core 10 of the present embodiment has an annular core. It was formed by cutting, and the original annular core was used for comparison.

First, a comparison will be made between the case of a / b = 24 and the case of an annular core. When a / b = 24, frequency 100
At MHz, a value of approximately 108.7 ohms was obtained. This is a larger value than the annular core. And a / b
The curve of = 24 and the curve of the annular core both increase the impedance as the frequency increases, but both curves are about 30 MH
It intersects in the vicinity of z, and below that, it becomes smaller in the case of a / b = 24.

That is, in the case of a / b = 24, it becomes slightly larger than the annular core in the frequency band of 100 MHz or more where noise is likely to occur, and the impedance decreases in the vicinity of the signal band of several tens of MHz as compared with the annular core. is doing. Therefore, the signal line SL having a relatively low frequency band
Attenuating the signal flowing through the signal is reduced and the adverse effect on the signal is allowed to pass through as much as possible, and a damping effect equal to or higher than that of the annular core is obtained with respect to high frequency noise.

Further, as the ratio a / b becomes smaller, the impedance is lowered as a whole, but as shown in FIG.
Even when / b is 9, the impedance in the high frequency band can be obtained up to 80% or more of the impedance without the gap. For example, it is about 80% in the case of 100 MHz, and the difference between the two gradually decreases as the frequency increases further.

Then, in the vicinity of several tens of MHz, the impedance becomes considerably lower than that in the case of the annular core. Therefore, when it is desired to further lower the impedance in the low frequency band and further reduce the adverse effect on the signal flowing through the signal line SL, it is desirable to set the ratio a / b to a low value.

As described above, when the U-type ferrite core 10 satisfying the above-mentioned predetermined conditions is used, the adverse effect on the signal in the relatively low frequency band is passed as small as possible, and the high frequency noise is circular. Since a damping effect equivalent to or greater than that when using a core is obtained, a more practical noise filter can be realized.

Another aspect of the first embodiment will be shown. The U-type ferrite core 20 shown in FIG. 2A is installed on a substrate, for example, and functions as a noise filter for the lead wire LL as the signal wire SL. In this case, the “U” -shaped curved side (that is, the side opposite to the free ends 14 and 16) shown in FIG.
It is configured as 2. If this substrate contact surface 22 is placed on the substrate, stability is good.

Further, as a device for fixing the lead wire LL, there is one shown in FIGS. 2 (B) to 2 (D). (B) and (C) are top views of the U-shaped ferrite core 20,
(B) shows insertion holes 24 and 26 which are penetrated from the bottom portion 12 to the substrate contact surface 22 side in order to insert the lead wire LL, and (C) is for fixing the lead wire LL to the edge of the bottom portion 12. The concave portions 26 and 27 are formed. Also,
(D) shows a bent portion LL1, which is formed by bending the lead wire LL.
LL2 is formed so as to be engaged with the substrate contact surface 22 in (A). Of course, these ideas may be adopted in the U-type ferrite core 10 shown in FIG. [Second Embodiment] FIG. 4A is a perspective view showing a C-type ferrite core 30 used in a noise filter according to a second embodiment of the present invention, and FIG. The C-type ferrite core 30 is formed in a substantially C-shape with a constant thickness, and more specifically, as shown in (B), a part of a regular ring having an outer diameter R and an inner diameter r is cut out. It is a "C" formed by. The length of the average magnetic path (in this case, the magnetic path in the form of a positive ring having an intermediate diameter between the outer diameter R and the inner diameter r) is "L", and the two free ends 34 formed by the cutout are The distance on the average magnetic path between 36 (hereinafter referred to as the magnetic path gap) is "Lg", and the magnetic path gap Lg is set to be 1 to 25% of L of the average magnetic path length. Then, the signal line SL is arranged in the hollow portion 38.

FIG. 5 shows the results of examining the relationship between the ratio (Lg / L) and the impedance-frequency characteristics in this C-type ferrite core 30. The core used in this experiment has an outer diameter R = 14 mm and an inner diameter r = 10 mm. In Figure 5,
Magnetic path gap Lg = 4% (Lg / L = 0.04)
And magnetic path gap Lg = 25% (Lg / L = 0.2
The case of 5) and the case of the positive ring-shaped core without the magnetic path gap Lg are shown by broken lines for comparison. The C-type ferrite core 30 of this embodiment is formed by cutting a positive ring-shaped core, and the original positive ring-shaped core is used for comparison.

FIGS. 4C and 4D are side views showing the appearance of the C-type ferrite core 30 when the magnetic path gap Lg = 4% and when the magnetic path gap Lg = 25%, respectively. In addition, although a cut should be provided in the radial direction originally,
As shown in FIG. 4C, when the magnetic path gap Lg is narrow,
Forming both free ends 34, 36 in parallel has substantially no effect.

Referring to FIG. 5, first, the magnetic path gap Lg = 4.
% (Lg / L = 0.04) and the case of the positive ring-shaped core are compared. When the magnetic path gap Lg = 4%,
A value of about 41.0 ohms was obtained at a frequency of 100 MHz. The impedance of both the curve of the magnetic path gap Lg = 4% and the curve of the positive ring-shaped core increases as the frequency increases, but both curves intersect at a frequency of about 100 MHz, and below that, the magnetic path gap Lg = 4. %, The magnetic path gap becomes smaller, and the magnetic path gap Lg =
4% is larger. That is, in the frequency band of 100 MHz or higher where noise is likely to occur, the frequency is larger than that of the positive ring core, and the impedance is lower than that of the positive ring core in the vicinity of the signal band of several tens of MHz. In particular, the degree of decrease is very large around 10 to 60 MHz.

Therefore, a signal flowing through the signal line SL having a relatively low frequency band is passed through with a small degree of attenuation and a bad influence on the signal is passed as much as possible, and a high frequency noise is positive. A damping effect equivalent to or better than that of the ring-shaped core can be obtained. Further, when the ratio of the magnetic path gap Lg becomes large (that is, the ratio Lg / L becomes large), the impedance decreases as a whole. However, as shown in FIG. 5, the magnetic path gap Lg is 25%. However, the impedance in the high frequency band can be obtained up to 80% or more of the case without the magnetic path gap Lg. For example, it is about 80% in the case of 100 MHz, and the difference between the two gradually decreases as the frequency increases further.

In the vicinity of several tens of MHz, the impedance is considerably lower than that in the case of the positive ring core. Therefore, when it is desired to further lower the impedance in the low frequency band to further reduce the adverse effect on the signal flowing through the signal line SL, it is desirable to set the ratio of the magnetic path gap Lg, that is, the ratio Lg / L to a low value.

As described above, when the C-type ferrite core 30 satisfying the above-mentioned predetermined conditions is used, the adverse effect on the signal in the relatively low frequency band is passed as small as possible, and it is positive for the high frequency noise. Since a damping effect equivalent to or greater than that when the ring-shaped core is used, a more practical noise filter can be realized.

Next, a case for the U-type ferrite core 10 and the C-type ferrite core 30 described in the first and second embodiments will be described. FIG. 6 (A)-
(C) shows the case 50 for fixing the signal line for the U-type ferrite core 10, and (D) and (E).
Shows the holding case 60 of the C-type ferrite core 30.

First, the signal line fixing case 50 for the U-shaped ferrite core 10 will be described. The main fixing case 50 is made of resin or the like, and basically the U-shaped ferrite core 1 is used.
The hollow shape is slightly larger than the outer shape of 0, and the U-shaped ferrite core 10 can be housed just inside. Then, in the portion of the U-shaped ferrite core 10 facing the hollow portion 18 (see FIG. 1), the saw-like step 5 is formed on one side thereof.
A plurality of 2 are formed.

As a method of use, the U-type ferrite core 10 is housed and used, of course.
In the case of the single-line signal line SL as shown in (B), it is desirable to dispose the signal line SL at the innermost position (that is, near the bottom of the U-type ferrite core 10 shown in FIG. 1). Further, as shown in FIG. 6 (C), even when the flat cable FC is used, the serrated step 52 preferably prevents the flat cable FC from being displaced with respect to the flat surface.

Next, the holding case 60 for the C-type ferrite core 30 will be described. The holding case 60 is made of resin or the like, and basically has a hollow shape slightly larger than the outer shape of the C-type ferrite core 30 so that the C-type ferrite core 30 can be housed therein. Then, in the portion corresponding to the magnetic path gap Lg (that is, between both free ends 34 and 36) in the C-type ferrite core 30, there are convex portions 64 and 66 whose tips are in contact with each other as shown in FIG. , One set is formed on each side.

As a method of use, the C-type ferrite core 30 is housed and used, of course, but the signal line S
In order to put L into the inside, the protrusions 64 and 66 are pushed and inserted. Since the holding case 60 itself is made of resin or the like, the convex portions 64 and 66 can be deformed and inserted. Then, once the signal line SL is arranged inside, the convex portions 64 and 66 are in contact with each other, so that they do not easily move to the outside.

Since the signal line fixing case 50 and the holding case 60 are for the U-type ferrite core 10 or the C-type ferrite core 30 in which the existence of the magnetic path gap Lg is positively recognized, the conventional split type is used. Since it is not necessary to provide a lid and it is not necessary to bring the divided surfaces into close contact with each other, it is not necessary to provide a spring mechanism or the like. Therefore,
The case can be simplified. Further, as a matter of course, a basic case can compensate for the lack of mechanical strength of the ferrite core.

The present invention is not limited to the embodiments as described above, and can be carried out in various modes without departing from the gist of the present invention. For example, the C-type ferrite core 30 described as the second embodiment has a "C-shape" in which a part of a positive ring shape in which the outer diameter R and the inner diameter r are constant at each portion is cut out. The shape shown in FIG. 7 is also within the range of the “substantially C-shape” of the present invention.

The C-type ferrite core 130 shown in FIG.
Is a part of the ellipse cut away on the long axis side,
The (B) C-type ferrite core 132 has a part cut away on the minor axis side of the ellipse. Further, the C-type ferrite core 134 shown in (C) is a part of an annular shape close to a rectangle, specifically, a notch near the center of one side having a rectangle. Each magnetic path gap is indicated by Lg.

[0037]

As described in detail above, as described in claims 1 and 2, a noise filter using a substantially U-shaped ferrite core and a noise filter using a substantially C-shaped ferrite core are used. With both noise filters, the adverse effect on the signal in the relatively low frequency band is passed as small as possible,
With respect to high frequency noise, a damping effect equivalent to or greater than that of the case where the annular core is used is obtained, and a more practical effect that is more practical than ever is achieved.

[Brief description of drawings]

FIG. 1 shows a U-shaped ferrite core used in a noise filter according to a first embodiment of the present invention, (A) is a perspective view,
(B) is a side view.

FIG. 2 is an explanatory diagram showing another aspect of the first embodiment.

FIG. 3 is a graph showing the results of examining the relationship between the ratio (a / b) and the impedance-frequency characteristics in a U-type ferrite core.

FIG. 4 is a diagram showing a C used in the noise filter according to the second embodiment.
Type ferrite core, (A) is a perspective view, (B) ~
(D) is a side view.

FIG. 5: Ratio (Lg / L) in C-type ferrite core
3 is a graph showing the results of examining the relationship between impedance and frequency characteristics.

6A to 6C are side views showing a signal line fixing case for a U-shaped ferrite core,
(D) and (E) are a side view and a front view showing a holding case of a C-type ferrite core.

FIG. 7 is an explanatory diagram showing another aspect of the second embodiment.

[Explanation of symbols]

10, 20 ... U-type ferrite core, 12 ... Bottom part, 1
4, 16 ... Free end, 18 ... Hollow part, 22 ... Substrate contact surface, 24 ... Insertion hole, 26 ... Recessed part, 30, 130, 1
32,134 ... C-type ferrite core, 34, 36 ... Free end, 50 ... Signal line fixing case, 52 ... Saw-shaped step,
60 ... Holding case, 64 ... Convex portion,
SL ... signal line

Claims (2)

[Claims] 1. A ferrite core formed in a substantially U shape, wherein the distance from the inner bottom to the free ends is a and the distance between both free ends is b, and the ratio a / b thereof is 9 to. A noise filter characterized by using a ferrite core configured as No. 60, and arranging a signal line in a hollow portion of the ferrite core to attenuate noise flowing through the signal line. 2. A ferrite core formed in a substantially C shape, wherein the distance on the average magnetic path between both free ends is
A noise filter characterized by using a ferrite core configured to have an average magnetic path length of 1 to 25% and arranging a signal line in a hollow portion of the ferrite core to attenuate noise flowing through the signal line.