JPH11219832A - Choke coil for noise filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a choke coil for a noise filter, in which both a normal mode noise and a common mode noise can be reduced validly as noise reducing characteristic, and the noise reducing characteristic can be easily changed, without having to change the basic structure of the choke coil. SOLUTION: In a choke coil for a noise filter, an EE-type core 2 is constituted of two E-type cores 2a and 2a of magnetic materials. Then, coils 3 and 4 with the same number of turns are wound around a central magnetic leg 7, so that the direction of a magnetic flux due to load currents can be mutually made the same, and a sheet-shaped magnetic body 8a in a prescribed thickness or the sheet-shaped magnetic body 8a interposed between two insulating films 8b and 8b is inserted into a clearance 5 of each magnetic leg. As a result, prescribed magnetic coupling can be obtained. Both the normal and common mode noises can be reduced validly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a choke coil for a noise filter for removing noise generated in various electronic devices and affecting a power supply side or affecting the electronic devices.

[0002]

2. Description of the Related Art In an input line for supplying power to various electronic devices, ripple noise generated inside the electronic device affects a power supply side, or power containing such noise is input to the electronic device. This may be affected by noise interference, and a noise filter is generally inserted into the input line to remove such noise.

This noise filter is generally composed of a combination of a capacitor and a coil. In particular, a choke coil is often used as the coil. FIG. 2 shows an example of such a choke coil. The illustrated one is called a core type, and 1 is a commercial AC power supply, 2 is two E-shaped cores 2
This is an EE type core formed by facing a and 2a, and a magnetic material such as a silicon steel plate is used. Reference numerals 3 and 4 denote two coils having the same number of turns, which are wound around the outer legs of the EE-shaped core, respectively, and connected so that the directions of magnetic fluxes due to the load currents of the two coils are mutually added as indicated by dotted arrows. Have been.

[0004] Reference numerals 5a and 5b denote gaps, which constitute necessary gaps 5a and 5b with a film or paper interposed between two E-shaped cores to prevent saturation of magnetic flux. 6 is a load.
The center magnetic legs 7 of the two E-shaped cores 2a, 2a are provided without any gap so as to reduce the magnetic coupling between the coils.

[0005] Although not shown, two U-shaped cores made of silicon steel plate are opposed to each other and belong to the inner iron shape, and two E-shaped cores made of thin ferrite are stacked on top of each other. Some have coils wound on the outer legs.
This structure produces an effective impedance in the harmonics of the power supply frequency and in the EMI region.

FIG. 3 shows an example of what is called a shell type.
The core is made of two EE type cores or Japanese character type cores, and a magnetic material having high magnetic permeability such as ferrite is used. The coils 3 and 4 wound around the center magnetic leg 7 have the same number of turns and are wound such that the directions of the magnetic fluxes due to the load current In cancel each other as shown in FIG. An example of such a shell-type choke coil is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-28821.
No. 1 discloses this.

[0007]

By the way, generally, noise propagating through an input line such as a switching device includes:
A normal mode noise current In flowing on a line so as to reciprocate two cords of an input line and noise generated by an electronic device or the like pass through the ground and enter the middle of the line and travel in the same direction on the two lines. There is a common mode noise current Ic flowing back to the source.

In the above-described example of the core type choke coil, the normal mode noise is effectively reduced, but the inductance of the common mode noise is small because the directions of the magnetic fluxes cancel each other, so that there is almost no reduction effect. Conversely,
In the case of the outer core type, as shown in FIG. 3B, the inductance Ln is small for the normal mode noise generated in the load loop and has little noise reduction effect, but the direction of the magnetic flux for the common mode noise is small. Are in the same direction, the inductance Lc of common mode noise is large, and noise reduction is effectively performed.

As described above, the inner iron type effectively reduces the normal mode noise, and the outer iron type effectively reduces the common mode noise.
Since the noise of each other cannot be effectively reduced,
In order to effectively reduce both noises, two types of chokes, an inner iron type and an outer iron type, are used.

Also, depending on the electronic equipment used for the input line, the noise reduction characteristics required for the noise filter may not be effective at the same ratio in both the normal mode and the common mode. For example, the normal mode inductance Ln On the other hand, the common mode inductance Lc may be about a fraction of the case.

However, the ratio of inductance in the above-described conventional inner iron type and outer iron type does not match the noise reduction characteristics required for the line to be used. Then change the cross-sectional area of the central magnetic leg,
In the case of a shell type, it is necessary to start over from the beginning of production, such as changing the interval between two coils, and it is very difficult to change the inductance ratio after all.

According to the present invention, both normal and common mode noise can be effectively reduced as noise reduction characteristics.
It is an object of the present invention to solve the above problem by using a choke coil for a noise filter that can easily change the ratio of noise reduction characteristics without changing the basic structure of the choke coil.

[0013]

According to the present invention, as a means for solving the above-mentioned problems, two E-shaped cores made of a magnetic material are arranged to face each other to constitute an EE-shaped core, and the center magnetic leg of the E-shaped core is provided. A coil having the same number of turns is wound so that the directions of magnetic fluxes due to the load current are the same as each other, and a gap of a predetermined dimension is provided between the surfaces of the E-shaped cores where the magnetic legs face each other. The noise filter choke coil is formed by inserting a sheet-shaped magnetic material into the coil.

According to the choke coil for a noise filter having such a configuration, noise interference is removed as follows. E
In the E-shaped core, coils of the same number of turns are wound around each of the center magnetic legs, so that when a load current supplied from an external power supply circuit flows, the magnetic fluxes of the respective coils are in the same direction as each other. . Therefore, even when normal mode noise is input from the external power supply circuit, the noise is effectively reduced by the normal inductance, and the influence of noise disturbance on the electronic device of the load is prevented.

On the other hand, common mode noise generated in the electronic equipment of the load propagates in the same direction on two lines from the load to the load via the ground terminal, reaches the coils, and is generated by the respective coils generated by the common mode current. Although the magnetic fluxes are in opposite directions, two independent E-shaped magnetic paths are formed by the two E-shaped cores and the sheet-like magnetic material. Therefore, effective common inductance is generated, and common mode noise is prevented from being transmitted to the external power supply circuit.

Further, since a sheet-like magnetic material is inserted into the gap between the respective magnetic legs of the EE type core, if the thickness of the sheet-like magnetic material is set to a predetermined thickness, the choke coil of the choke coil can be prevented from normal or common mode noise. Necessary inductance values can be obtained without changing the basic shape. You may make it insert an insulating film with a sheet-shaped magnetic body.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration diagram of a choke coil for a noise filter according to the embodiment. Symbols 1 to 5 in the figure
Reference numeral 7 is basically the same as that of the conventional example, and different points will be mainly described below. 2 wound on the center magnetic leg 7
The coils 3 and 4 have the same number of turns, but are wound so that the directions of magnetic fluxes due to the load current flowing through the coils are mutually added in the same direction.

In the illustrated example, the coil 4 is wound in the same direction as the coil 3 in order to make the direction of the magnetic flux the same, and in the example shown in FIG. Is connected to the power supply line, and the end of the coil is connected to the load line. Although illustration is omitted, contrary to the illustrated example,
The coil 4 may be wound in a direction opposite to that of the coil 3, with the base end of the coil connected to a load line and the front end of the coil connected to a power supply line.

A gap 5 having a predetermined size (for example, 1 to 2 mm) is provided between the end faces of the two E-shaped cores 2a, 2a, 2a, 2a and 2a. In the gap 5, a sheet-shaped magnetic body 8a for adjusting the degree of magnetic coupling by the two coils 3, 4 and two insulating films 8b, 8b sandwiching the magnetic body 8a for preventing magnetic flux saturation due to a load current. Is inserted at an appropriate thickness.

As the sheet-like magnetic body 8a, a material having high magnetic permeability such as ferrite is used. Alternatively, only the sheet-shaped magnetic body 8a may be inserted into the gap 5.

The noise filter choke coil according to the embodiment configured as described above eliminates noise interference as follows. As shown, a normal mode noise current I is supplied from an external power supply side to an input line provided with the choke coil.
n is input on the load current, this current I
The direction of the magnetic flux by n is as shown by the dotted arrow in the figure,
It occurs in the direction that is added in the same direction. For this reason, the normal mode noise is sufficiently effectively reduced by the normal inductance Ln having a sufficient value, so that the normal mode noise from the outside does not affect the load by noise interference.

On the other hand, the common mode noise current Ic generated in the load 6 of the electronic device propagates in the same direction on two lines connected to the load and passes through the two coils 3 and 4, which occurs at that time. Although the magnetic fluxes are in opposite directions, the sheet-shaped magnetic body 8a and the E-shaped cores 2a, 2a form independent magnetic paths. Therefore, a sufficiently effective reduction effect is produced by a sufficient value of the common inductance Lc for the common mode noise.

As described above, there is an effective reduction effect on both normal mode and common mode noise, but the noise reduction characteristics as a noise filter using the choke coil of this embodiment are variously varied depending on the application. In such a case, in this embodiment, the sheet-like magnetic body 8a inserted into the gap 5 or the magnetic body 8a and the insulating film 8
When the thicknesses of b and 8b are changed, the coupling coefficient K between the coils changes, so that the normal inductance Ln and the common inductance Lc of the coils can be variously changed.

Each inductance L and coupling coefficient K
Is expressed by the following approximate expression. Here, L is the inductance of one coil 3.

Ln ≒ 2L (1 + K) Lc ≒ L (1−K) / 2 As can be seen from the above description, by changing the thickness of the sheet-like magnetic material 8a or the thickness of the magnetic material 8a and the insulating films 8b, 8b, Therefore, if the magnetic material 8a or the magnetic material 8a and the insulating films 8b, 8b having various thicknesses are prepared in advance, they can be inserted according to the required noise reducing characteristics. This can be handled by selecting a thickness that is appropriate.

Since the inductance of the coil and the value of the coupling coefficient K obtained by the above equation are theoretical values, actual values of L and K are actually measured for a thickness corresponding to the theoretical value. The insert having the noise reduction characteristics obtained by the actual measurement may be appropriately selected according to the application.

In the above-described embodiment, the gap 5 is provided between the end faces of the central magnetic legs of the two E-shaped cores 2a, 2a and the two outer magnetic legs facing each other. Reference numeral 5 may be provided only between the center magnetic legs 7 and 7, and the sheet-like magnetic body 8 a or the sheet-like magnetic body 8 a and two insulating films 8 b and 8 b may be inserted into the gap 5.

[0028]

EXAMPLE The sheet-like magnetic body 8a described in the above embodiment is described.
The relationship between the coupling coefficient K and a predetermined thickness was measured using ferrite. In this case, the required characteristics of the choke coil for the noise filter are assumed to be Ln (normal inductance) = 10 mH Lc (common inductance) = 1.8 mH, and the values of the magnetic material 8a and the coupling coefficient K corresponding to this are measured by actual measurement. Obtained as follows.

First, when the inductance L and the coupling coefficient K of the above-mentioned coils Ln and Lc are obtained from the above-mentioned theoretical formula, K = 0.16 L = 4.4 mH.

In order to realize this value, the core shape EE2
8, thickness 10mm, sheet-like magnetic material (ferrite)
8a with a thickness of 1.0 mm and 0.5 mm, the coupling coefficient K
When the value was measured, the thickness of the magnetic material (mm) and the coupling coefficient (K) 1.0 0.078 0.5 0.128 were obtained.

From the above measured values, the thickness of the magnetic material was 0.5 m
It can be seen that a value of about m is close to the target value.

[0032]

As described above in detail, the choke coil for a noise filter according to the present invention has two E-shaped cores each having the same number of windings on the center magnetic leg of the EE-shaped core and the direction of the magnetic flux due to the load current. It is wound in the same direction as each other, and a sheet-like magnetic material is inserted into the gap provided between the magnetic legs. Therefore, the noise reduction characteristic is obtained by appropriately setting the thickness of the sheet-like magnetic material. Therefore, it is possible to obtain the effect that the required reduction characteristics as a noise filter can be obtained only by changing the thickness of the sheet-shaped magnetic body without changing the basic structure of the choke coil. Can be.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a choke coil for a noise filter according to an embodiment.

FIG. 2 is a schematic configuration diagram of a choke coil for a noise filter according to an embodiment.

FIG. 3 is a schematic configuration diagram of another choke coil for a noise filter.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 commercial AC power supply 2 EE type core 3, 4 coil 5 gap 6 load 7 center magnetic leg 8 a sheet-like magnetic body 8 b insulating film

Claims (3)

[Claims] An EE-type core is constituted by arranging two E-type cores of a magnetic material opposite to each other, and coils having the same number of turns are provided on each of the central magnetic legs of the E-type core in the same direction of a magnetic flux due to a load current. A choke coil for a noise filter, which is wound in such a manner that a gap of a predetermined size is provided between the surfaces of the E-shaped cores facing the respective magnetic legs, and a sheet-like magnetic material is inserted into the gap between the respective magnetic legs. 2. The choke coil for a noise filter according to claim 1, wherein an insulating filter is further inserted into the gap. 3. The choke coil for a noise filter according to claim 1, wherein the gap is provided only between surfaces of the E-shaped core facing the central magnetic leg.