JPH0291905A - Inductor for noise filter - Google Patents

Abstract

PURPOSE:To enable the title inductor to work effectively on noises of both common mode and normal mode by making a pair of ferrite cores each having three leg sections butt to each other, with two leg sections provided with windings, and the remaining leg sections provided with a gap between their parts facing each other. CONSTITUTION:A pair of ferrite cores 4 and 5 have three leg sections 6, 7, 8 and 9, 10, 11 respectively, and they are put together contacting or facing each other at these leg sections 6, 7, 8 and 9, 10, 11. Window sections 12 and 13 with respective rectangular plane shapes are formed between leg sections 6, 8 and 9, 11 and the central leg sections 7, 10. Besides, coils 14 and 15 with specified numbers of turns are wound respectively at the both side leg sections 6, 8 and 9, 11 through the window sections 12 and 13. In addition, a gap (g) is formed at the remaining leg sections, that is, at the facing section of the central leg sections 7 and 10. This way makes it possible for the inductor to work effectively on both noises of common mode and normal mode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inductor for a noise filter that attenuates noise generated in an electric circuit.

[Summary of the invention]

The present invention provides an inductor for a noise filter that attenuates noise generated in an electric circuit.In addition to the two legs around which the winding is wound, the core is further provided with a leg that absorbs leakage magnetic flux. The present invention provides a noise filter inductor that effectively acts on both common mode noise and normal mode noise.

[Conventional technology]

Noise is generated in electrical circuits due to various factors. The above noise is mainly divided into normal mode noise and common mode noise.

The normal mode noise mentioned above is, for example, when two circuits overlap and have a common area, or when two circuits are wired in parallel as a wire bundle due to wiring reasons, the magnetic flux generated by the current flowing in one circuit is transferred to the other circuit. An induced electromotive force is generated in the other circuit through the stray capacitance (stray capacitance) between the lines or between the lines, and this induced electromotive force is added to the voltage of the other circuit and mutually suppresses the noise of the other circuit. This refers to the noise bone in question. That is,
The noise voltage when a noise voltage is applied in series with the signal voltage is normal mode noise.

On the other hand, common mode noise refers to, for example, when a circuit configuration is adopted in which current from another circuit flows between the ground points, even a small amount of resistance between the ground points causes a potential difference between them, and the overall circuit Refers to the amount of voltage change in which the potential relative to ground fluctuates.

In other words, the voltage change that occurs other than the signal with respect to the ground potential is called common mode noise.

In such an electric circuit where normal mode noise and common mode noise coexist, a filter having a circuit configuration as shown in FIG. 8, for example, is usually provided for the purpose of attenuating these noises. For example, as shown in FIG. 9, the inductor T used in the above filter has a ring-shaped core (1) with windings (2) on both legs, respectively.
(3) is wound a predetermined number of times.

[Problems to be Solved by the Invention] However, in the inductor T having the above configuration, as shown in FIG. 9, each coil <
2), (3) The magnetic flux (ψ
)・acts effectively to attenuate the noise, but for normal mode noise, as shown in Figure 10, the magnetic flux (
Since the coils (ψ) and (ψ) act to cancel each other out, the noise cannot be attenuated, and the coils (2) and (3
) only the leakage magnetic flux caused by poor coupling affects normal mode noise.

Therefore, conventionally, in an electric circuit in which normal mode noise and common mode noise coexist, an inductor T that effectively acts on common mode noise and a coil L that acts effectively on normal mode noise, as shown in Figure 11.
1. L! and are placed in the same circuit to attenuate these noises.

However, in the same circuit, there is a noise filter inductor T and coils Ll, L! If such a filter is arranged, the number of parts of the filter increases and the filter becomes large, which is a major hindrance to miniaturizing electrical equipment.

Therefore, the present invention has been proposed in view of the conventional situation, and provides a filter inductor that can effectively utilize leakage magnetic flux and that effectively acts on both common mode noise and normal mode noise with one inductor. The purpose is to provide

[Means for Solving the Problems] In order to achieve the above object, the noise filter inductor of the present invention is made up of a pair of ferrite cores each having three legs butted against each other. It is characterized in that a winding wire is wound around two of the legs, and a gap is formed in the abutting surfaces of the remaining legs.

According to the noise filter inductor of the present invention, the core has at least three legs, and a winding is wound around two of these legs, so that common mode noise can be prevented. The magnetic flux generated by the current flowing through each winding effectively acts to attenuate noise without canceling each other out.

In addition, for normal mode noise, the magnetic flux generated by the current flowing through each of the windings flows to the remaining legs where the windings are not wound, so the leakage magnetic flux can be used effectively. Noise is attenuated.

Therefore, attenuation of both the common mode noise and normal mode noise is achieved with one inductor.

Furthermore, according to the noise filter inductor of the present invention,
Since a gap is formed in the abutting surfaces of the legs where the winding is not wound, saturation of the electric circuit in this part can be prevented, and thereby a large current can be passed through the winding.

[Effect]

[Example] Hereinafter, a specific example to which the present invention is applied will be described with reference to the drawings.

As shown in FIG. 1, the noise filter inductor of this embodiment is constructed by butting together a pair of ferrite cores (4) and (5) each having an E-shaped planar shape.

The pair of ferrite cores (4) and (5) have three legs (6), (7), (8) and (9), respectively.
), (10), (11), and these legs (6),
(7), (8), (9), (10) and (11) are butted together as abutting surfaces. Therefore, between the legs (6), (8), (9), (11) on both sides and the legs (7), (10) in the center, there are windows ( 12) and (13) are formed. In addition, the legs (6), (7),
(8) and (9), (10).

Among (11), the legs (6), (8) and (
A predetermined number of windings (14) and (15) are wound around windows 9) and (11) through the windows (12) and (13), respectively. Also, the remaining legs, i.e. the middle leg (
A gap g is formed between the abutting surfaces of 7) and (10). The gap g is defined by the central leg (7).
It is formed by providing a gap of a predetermined distance between the abutting surfaces of (10) and (10), which is a so-called air gap.

The noise filter inductor configured in this way is
For common mode noise, as shown in Figure 2,
The legs (6), (8) and (9) on both sides.

Windings (14) and (15) respectively wound on (11)
) The magnetic flux (ψ1) generated by the currents 11 and 12 flowing in
and (ψ2) are all in the same direction, that is, a closed magnetic path is formed so as to surround both windows (12) and (13), thereby attenuating the common mode noise.

On the other hand, for normal mode noise, as shown in Figure 3, the magnetic fluxes (ψ1) and (ψ1) generated by the currents i and h flowing through the windings (14) and (15) cancel each other out. Both legs in the center (7)
and (10), and the respective windows (12) and (1
3) A closed magnetic circuit is constructed to surround the circuit to attenuate normal mode noise. That is, ferrite core (4)
Since the legs (7) and (10) are provided in the center of and (5), leakage magnetic flux is absorbed there, and this leakage magnetic flux attenuates normal mode noise.

Therefore, the above-mentioned noise filter inductor effectively acts on both common mode noise and normal mode noise with a single inductor. Further, if the noise filter inductor is placed in an electric circuit where these common mode noises and normal mode noises coexist, an excellent filtering effect can be expected. Furthermore, since the noise filter inductor is a single inductor that effectively acts against any kind of noise, the number of parts can be reduced and the size can be reduced. Therefore, further miniaturization of electrical equipment and the like can be realized.

In addition, since the above-mentioned noise filter inductor has a gap g formed between the abutting surfaces of the central legs (7) and (10), saturation of the magnetic path in this part can be prevented, and this prevents the winding ( It becomes possible to flow a large current through 14) and (15).

In 22, the above-mentioned noise filter inductor was actually manufactured based on the following conditions, and its characteristics as a filter were investigated. In addition, in order to compare with the noise filter inductor of this example, the filter characteristics of a conventional noise filter intalor formed by winding a wire around a ring core were similarly investigated.

In the noise filter inductor of this example, the length of the inductor is 25.5 cm (error ±0.5), the height H in the direction where the legs meet is 19 cm (error ±0 °5), and the width W
The cross-sectional area S of the central leg was 0°44C4, the gear +7 length was 0.25 AL, and the winding was 40 turns to give an inductance of 1 mH.

Note that the inductance of the noise filter inductor formed by winding a wire around a ring core was also 1 mH.

First, the characteristics between impedance and frequency were investigated. The results are shown in Figure 4. In measuring the characteristics of the impedance and interwave number, the measurement frequency was set to 101 (z ~ 1
The range was 0 MHz.

As a result, in an inductor with a wire wound around a ring core, the resistance to common mode noise is as shown by curve A.
A peak value appears in impedance at a certain frequency, after which it exhibits characteristics similar to capacitance. On the contrary,
In the noise filter inductor of this embodiment, as shown by curve C, a first peak value appears in impedance at a certain frequency, and then a second peak value appears in impedance again at a certain frequency. . That is,
In the noise filter inductor of this example, the leakage magnetic flux is absorbed by the central legs (7) and (10), so the first
After the peak value of , a peak value appears in the impedance again. Therefore, it can be seen that the noise filter inductor of this example has a wider frequency band and an increased effect as a filter.

On the other hand, for normal mode noise, as shown by curve B, in an inductor with a wire wound around a ring core,
In the measurement frequency range, there is no impedance peak at all, and on the contrary, it shows a value close to zero.On the other hand, the noise filter inductor of this example has an impedance peak at a certain frequency, as shown by the curved line. is,
It can be seen that this has an effective effect on normal mode noise.

Next, we investigated the DC superposition characteristics. The results are shown in FIG.

As can be seen from FIG. 5, the DC superimposition characteristics against common mode noise are the same for both the inductor in which the winding is wound around the ring core (indicated by curve E) and the inductor of this example (indicated by curve G). On the other hand, the DC superimposition characteristics against normal mode noise are considerably worse for the inductor in which the winding is wound around the ring core (shown by curve F), but for the inductor of this example ( Curve I (
) showed good values.

Furthermore, the damping characteristics were also measured.

As a result, the inductor of this example exhibited better characteristics against both common mode noise and normal mode noise than an inductor in which a wire was wound around a ring core.

As can be seen from the above measurement results, according to the noise filter inductor of this embodiment, one inductor effectively acts against not only common mode noise but also normal mode noise. Therefore, if the inductor is placed in an electric circuit where common mode noise and normal mode noise coexist, a tremendous filtering effect can be obtained.

Note that the present invention is not limited to the embodiments described above, and can be modified in various ways. For example, the number of legs of the ferrite core does not necessarily have to be three, and it is sufficient if the ferrite core has at least three or more legs.

In this case, it is sufficient that the winding wire is wound around two of these legs, and a gap is formed between the abutting surfaces of the remaining legs.

Regarding the gap, it is not necessary that the butt faces of the butt legs be a gap, for example, the 6th
As shown in the figure, a part of the abutting surfaces of the legs (16) and (17) may be cut out to create a step-like gap g. Instead of an air gap, the gap film (20) may be formed by inserting a material having a 13ii ratio lower than the core's ili ratio between the legs (18) and (19).
Furthermore, adhesive mixed with ferrite powder is inserted into the legs (18) and (19), and the gap l1l (20
) is acceptable.

[Effects of the Invention] As is clear from the above description, according to the noise filter inductor of the present invention, in addition to the legs around which the winding is wound, leakage magnetic flux that effectively acts on normal mode noise is absorbed. Since the legs are further provided in the core, the leakage magnetic flux can be used effectively, and the two inductors effectively act against not only common mode noise but also normal mode noise.

Therefore, if the noise filter inductor of the present invention is placed in an electric circuit where common mode noise and normal mode noise coexist, a tremendous filter effect can be obtained.

In addition, since the above noise filter inductor effectively acts against any noise with just one inductor,
It can be miniaturized and is effective for further miniaturization of electrical equipment, etc.

[Brief explanation of the drawing]

Fig. 1 is a schematic perspective view showing an example of an inductor for a noise filter to which the present invention is applied, Fig. 2 is a schematic diagram showing the state of magnetic flux in common mode noise, and Fig. 3 is a schematic diagram showing the state of magnetic flux in normal mode noise. FIG. FIG. 4 is a characteristic diagram showing the impedance and frequency characteristics of the noise filter inductor of this embodiment and the conventional inductor. FIG. 5 is a characteristic diagram showing the DC superposition characteristics of the noise filter inductor of this embodiment and a conventional inductor. FIG. 6 is an enlarged front view of the main part of the gap section showing another example of the noise filter inductor to which the present invention is applied, and FIG. 7 is an enlarged front view of the main part of the gap section showing still another example. . FIG. 8 is a circuit diagram showing the circuit configuration of a conventional filter. FIG. 9 is a schematic diagram showing the state of magnetic flux in common mode noise of a conventional noise filter inductor, and FIG. 10 is a schematic diagram showing the state of magnetic flux in normal mode noise. FIG. 11 is a circuit diagram showing another circuit configuration of a conventional filter. 4.5... Ferrite core 6.7, 8, 9.10. li...leg 14.15...
・Winding

Claims (1)

[Claims] A pair of ferrite cores each having at least three legs are butted against each other, a winding is wound around two of these legs, and the abutting surfaces of the remaining legs are wound together. An inductor for a noise filter, characterized in that a gap is formed in the inductor.