JPH0233390Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to a noise filter having a configuration in which a plurality of common mode choke coils are connected in cascade.

(Description of Prior Art) Fig. 1 shows the overall structure of a conventional noise filter having a configuration in which two common mode choke coils are connected in cascade, and Fig. 2 shows its circuit diagram.
FIG. 3 shows a connection between two common mode choke coils.

In these figures, metal shield case 1
Insulated terminal plates 2 and 3 are inserted and fixed to the insulated terminal plate 2, and a pair of input/output terminals 4A and 4 are attached to the insulated terminal plate 2.
B and a ground terminal 5 are provided, and the insulated terminal board 3 is provided with a pair of input/output terminals 6A and 6B. Two common mode choke coils 7 and 8 are arranged within the shield case 1, and the common mode choke coils 7 and 8 are connected in cascade. That is, one end of the winding 7A, 8A of the two common mode York coils 7, 8 is connected in series, one end of the winding 7A is connected to the input/output terminal 4A, and one end of the winding 8A is connected to the input/output terminal. 6A, the other windings 7B and 8B are connected in series, one end of the winding 7B is connected to the input/output terminal 4B, and one end of the winding 8B is connected to the input/output terminal 6B. Here, the windings 7A and 7B of the common mode York coil 7 are set in a winding direction such that the magnetic fluxes generated by the power supply current In flowing in the direction indicated by the arrow in FIG. 2 cancel each other out. There is. The same applies to the windings 8A and 8B of the common mode York coil 8. In addition, the input/output terminals 4A, 4B
An interline capacitor 9 is connected between the lines and between 6A and 6B.
10 are connected to each other, and further, an interline capacitor 11 is connected between the connection point between the windings 7A and 8A and the connection point between the windings 7B and 8B. Also, winding 7
Line-to-ground capacitors 12 and 13 are connected between the connection point of A and 8A and the connection point of windings 7B and 8B and the shield case 1. Note that a ground connection piece 14 is provided to connect the ground terminal 5 and the lid portion of the shield case 1.

FIG. 4 shows the frequency characteristics of the attenuation amount of the conventional noise filter, in which the solid line P is the attenuation amount for normal mode noise, and the dotted line Q is the attenuation amount for common mode noise. However, the common mode choke coils 7 and 8 have an outer diameter of 38 mm and an inner diameter.
It is a toroidal ferrite core of 22 mm and 14 mm in height with a winding of 4 mH each, the capacitors 9, 10, 11 between lines are 0.27 μF, and the capacitors 12, 13 between line and ground are 4700 pF.
In this case, there is a tendency that sufficient attenuation for normal mode noise around 200 kHz cannot be obtained.

As a result of investigating the cause, the present inventor found that in the conventional noise filter as described above, no consideration was given to the connection relationship (winding direction) between the windings of the adjacent common mode choke coils 7 and 8. We found that the cause was in the following points. In other words, it is thought that the amount of attenuation against normal mode noise of the common mode choke coils 7 and 8 is obtained by the leakage inductance of each winding, but in the above conventional configuration, as shown in FIG. line 7
The direction of rotation of the magnetic flux caused by the current passing through the winding portions u and v that are close to each other and opposite each other at A and 8A is as shown by the arrow in the figure, and the magnetic fluxes cancel each other out in the space between the winding portions u and v. The same thing can be said about windings 7B and 8B. This means that the leakage inductance of each winding of the common mode choke coils 7 and 8 is reduced, and as a result, it is recognized that the amount of attenuation of normal mode noise in the vicinity of 200 kHz is reduced.

(Purpose of the invention) Therefore, the present invention focuses on the connection relationship (winding direction) of the windings when common mode cheese coils are connected in cascade, and the winding portion facing the adjacent common mode cheese coil. The present invention attempts to provide a noise filter that improves the attenuation characteristics against normal mode noise by setting the winding direction of each common mode choke coil so that the magnetic fluxes are mutually added.

(Embodiments of the invention) Hereinafter, embodiments of the noise filter according to the invention will be described with reference to the drawings.

FIG. 5 shows the overall structure of the embodiment, and FIG. 6 shows the connecting portion of two common mode choke coils.

In these figures, metal shield case 1
Inside, there are two common mode choke coils 7',
8 is placed. Here, the common mode chiyoke coil 7' has the windings drawn out in the opposite direction from the conventional common mode chiyoke coil 7 shown in FIG. Common mode choke coil 7', 8
are connected in cascade, that is, one winding 7A', 8A of the two common mode choke coils 7', 8
are connected in series, one end of the winding 7A' is connected to the input/output terminal 4A, one end of the winding 8A is connected to the input/output terminal 6A, and the other winding 7B',
8B are connected in series, one end of the winding 7B' is connected to the input/output terminal 4B, and one end of the winding 8B is connected to the input/output terminal 6B. Note that the other configuration may be the same as that in FIG. 1.

According to this embodiment, as shown in FIG. 6, the adjacent winding portions x,
The direction of magnetic flux change due to the current passing through v is as shown by the arrow in the figure, and the magnetic fluxes are added to each other in the space between the winding portions x and v. The same applies to windings 7B' and 8B. This means that
This means that the leakage inductance of each winding of the common mode choke coils 7' and 8 increases.

FIG. 7 shows the frequency characteristics of the attenuation amount of the noise filter of the embodiment, in which the solid line R represents the attenuation amount for normal mode noise, and the dotted line S represents the attenuation amount for common mode noise. in this case,
The amount of attenuation for normal mode noise in the vicinity of 200 kHz to 500 kHz can be maintained sufficiently large, and this is recognized to be due to the increase in leakage inductance of each winding of the common mode choke coils 7' and 8 mentioned above.

(Effects of the invention) As explained above, according to the invention, when a plurality of common mode cheese coils are connected in cascade, the magnetic fluxes of the opposing winding portions of adjacent common mode cheese coils are added to each other. By setting the winding direction of each common mode choke coil as described above, it is possible to obtain a noise filter that can improve the attenuation characteristics against normal mode noise.

[Brief explanation of drawings]

Figure 1 is a plan view showing the overall structure of a conventional noise filter, Figure 2 is its circuit diagram, Figure 3 is an explanatory diagram showing the connection relationship between the windings of two common mode choke coils, and Figure 4. is a graph showing the frequency characteristics of attenuation in the case of a conventional noise filter, Fig. 5 is a plan view showing the overall structure of an embodiment of the noise filter according to the present invention, and Fig. 6 is a graph showing two common modes in the embodiment. FIG. 7 is an explanatory diagram showing the connection relationship of the windings of the York coil, and FIG. 7 is a graph showing the frequency characteristics of the attenuation amount in the case of the noise filter of the embodiment. 1... Shield case, 7, 7', 8... Common mode choke coil, 7A, 7B, 7'A,
7'B, 8A, 8B... winding, 9, 10, 11...
...Line capacitor, 12, 13...Line
Ground-to-ground capacitor.

Claims (1)

[Scope of utility model registration request] In a noise filter having a configuration in which a plurality of common mode chiyoke coils are cascade-connected, the series-connected winding portions of adjacent common mode chiyoke coils are closely opposed to each other, and the winding portions that are closely opposed to each other are A noise filter characterized in that the winding direction of each common mode choke coil is set so that the magnetic flux generated in the space between the winding parts due to the passing current is added to each other.