JPH05121255A - Noise filter - Google Patents

Abstract

PURPOSE:To provide a thin noise filter of good performance having composite choke coils. CONSTITUTION:A first normal mode choke coil is formed of windings 4 and 5 of the same turns wound on the two crosspieces in the middle of a rectangular core frame 20. A second normal mode choke coil is formed of windings 2 and 3 of the same turns wound on one of the two crosspieces and its adjacent side of the core frame. The first and second choke coils are connected in series to form a noise filter with its core grounded. In this manner, a thin, effective noise filter is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise filter,
In particular, the present invention relates to a noise filter in which a normal mode choke coil of a noise filter having a two-stage filter function is integrally combined.

[0002]

2. Description of the Related Art In recent years, small and lightweight switching power supplies have come to be used in electronic equipment. However, since noise is generated from the switching power supplies, it is necessary to use a noise filter to prevent noise propagation to the power supply line. There is.

As one of the configurations of the noise filter, as shown in FIG. 6, two normal mode choke coils 33 and 34 are provided.
There is a two-stage filter using. The terminal 19 is connected to the ground line of the power source or the ground side of the device via the capacitors 30 and 31. 32 is also a capacitor. 2, 3,
4, 5 are windings of each choke coil, 10, 11, 14,
15 is a terminal. Such a two-stage filter is often used because it has a great effect of attenuating noise, but it is large because it requires two choke coils. Therefore, a composite of normal mode choke coils has been proposed.

FIG. 7 is a perspective view showing an embodiment of a conventional composite choke coil. Reference numerals 40a and 40b are U-shaped magnetic cores, which are orthogonal magnetic cores formed by abutting each other so that the end faces of the legs thereof are orthogonal to each other. U-shaped magnetic core 40a, 4
The windings 41a and 42a are wound around the leg portions of 0b in the same number of turns, and the windings 41a and 42b are wound around the leg portions of the U-shaped magnetic core 40b in the same number of turns.
The winding 41b and the winding 42a and the winding 42b are connected in series.

Since the U-shaped magnetic cores 40a and 40b are butted so as to be orthogonal to each other at the end faces of the legs, the winding 41 is formed.
magnetic flux generated in the magnetic core 40a by a and 41b, and the winding 4
Since the magnetic fluxes generated in the magnetic core 40b by 2a and 42b are orthogonal to each other inside the magnetic core, mutual induction does not occur, and the independent common mode choke coils are configured. Since they are connected in series, it is a single composite choke coil, but a two-stage filter can be realized.

[0006]

However, in the above-mentioned conventional structure, since the legs of the U-shaped cores 40a and 40b are large in depth, the height is high as a whole, and it is difficult to make them thin.

Since the U-shaped magnetic cores 40a and 40b are joined together, they are also electrically connected. Capacitances exist between the U-shaped magnetic core 40a and the windings 41a and 42a, and between the U-shaped magnetic core 40b and the windings 41b and 42b, and the U-shaped magnetic cores 40a and 40b are electrically connected. Therefore, the windings 41a and 42a
There is also a problem that capacitance is generated between the windings 41b and 42b and the higher the frequency is, the lower the impedance becomes, and the noise prevention effect is significantly reduced.

The present invention solves the above-mentioned conventional problems, and an object thereof is to provide a high-performance noise filter with a thin composite choke coil.

[0009]

In order to achieve this object, the noise filter of the present invention uses an eye-shaped magnetic core having four magnetic legs, and the number of turns is set so as to straddle the inner two magnetic legs. The same two windings are applied to form a first normal mode choke coil, and two windings with the same number of turns are applied so as to straddle one magnetic leg on the inside and an outer magnetic leg adjacent to the one magnetic leg. As a choke coil for normal mode,
A composite choke coil in which a first normal mode choke coil and a second normal mode choke coil are connected in series is used.

Further, the eye-shaped magnetic core is connected to the ground. The bobbin around which the winding is wound is integrally formed.

[0011]

With the above structure, the magnetic flux generated by the first normal mode choke coil wound so as to straddle the inner two magnetic legs of the eye-shaped magnetic core is adjacent to the inner one magnetic leg. The magnetic flux is not changed in the winding of the second normal mode choke coil wound so as to straddle the outer magnetic leg, and conversely, the magnetic flux generated by the second normal mode choke coil is
Since the magnetic flux is not changed in the winding of the first normal mode choke coil, mutual induction does not occur between the first normal mode choke coil and the second normal mode choke coil. The choke coils independent of each other can be constructed. Since such a composite choke coil has an eye-shaped magnetic core, it can be made thinner than before.

By grounding the eye-shaped magnetic core, the capacitance between the first normal mode choke coil and the magnetic core and the capacitance between the second normal mode choke coil and the magnetic core are grounded. Since they are connected, the capacitance between the first normal mode choke coil and the second normal mode choke coil can be ignored, and there is no problem that the noise prevention effect at high frequencies is reduced.

Further, if the bobbin is integrally molded, the number of parts is reduced and the assembly becomes easy.

[0014]

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the first of the present invention.
6 is a top view showing a composite choke coil of the noise filter in the example of FIG. In FIG. 1, reference numeral 20 denotes an eye-shaped magnetic core, which is composed of four-leg magnetic cores 1a and 1b. Two
Reference numerals 3, 4 and 5 are windings, respectively, and windings 2 and 3 are the first normal mode choke coil, windings 4 and 5 respectively.
And constitutes a second normal mode choke coil. Reference numerals 6 and 7 are bobbins, and windings 2 and 3 are wound around the bobbin 6, and windings 4 and 5 are wound around the bobbin 7.

The operation of the composite choke coil constructed as above will be described with reference to FIGS. 2 and 6. FIG. 2 is a schematic diagram showing the operation of the first embodiment. In FIG. 2, windings 2, 3, 4, 5 and terminals 10, 11, 1
2, 13, 14, and 15 correspond to the numbers given in FIG.

In FIG. 2, the windings 4 and 5 are wound over the two magnetic legs inside the eye-shaped magnetic core 20. The windings 2 and 3 are wound so as to straddle the outer magnetic leg and the magnetic leg adjacent thereto. The magnetic flux generated by the power supply current has the same magnitude in the winding 2 and the winding 3, and the directions thereof are opposite to each other, so that the magnetic fluxes cancel each other out. Further, since the magnetic fluxes of the windings 4 and 5 are equal in magnitude and opposite in direction, the magnetic fluxes cancel each other out.

On the other hand, the normal mode noise is
11 or 14 and 15 are applied in the same phase. Figure 2
4 shows the magnetic flux when normal mode noise flows from the terminals 10 and 11. 16a and 16b are magnetic fluxes generated in the windings 2 and 3. 17a and 17b are windings 4
And the magnetic flux generated in 5. The magnetic flux 16a is the winding 4,
5 has no effect, but the magnetic flux 16b does not
Is flowing through the magnetic leg that is wound. However, as seen from the windings 4 and 5, since the magnetic flux 16b has the same magnitude in each magnetic leg and the directions are opposite to each other, the voltages induced in the windings 4 and 5 cancel each other out to zero, and as a result, The magnetic flux 16b will not affect the windings 4 and 5. Similarly windings 4 and 5
The magnetic flux 17b generated in 1 does not affect the windings 2 and 3,
7a also cancels each other with respect to the windings 2 and 3, so that no voltage is generated and there is no influence. In this way, winding 4, 5
The first normal mode choke coil configured by and the second normal mode choke coil configured by the windings 2 and 3 operate as independent choke coils.

The winding 2 and the winding 4 are connected in series, and similarly, the winding 3 and the winding 5 are also connected in series. If a circuit as shown in FIG. 6 is constructed using such a composite choke coil transformer, a two-stage filter can be constructed.

As described above, in the present invention, since the eye-shaped magnetic core 20 is used, the four magnetic legs are arranged in the same plane, which is thinner than the conventional orthogonal magnetic core which is three-dimensional. Is easy.

(Embodiment 2) A second embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a top view of a noise filter choke coil showing a second embodiment of the present invention. In FIG. 3, 18 is a bobbin and 23 is a grounding clamp. 1 is different from the configuration of FIG.
In FIG. 3, the windings 2 and 3 and the windings 4 and 5 are connected and wound, but in FIG. 3, the windings 2 and 4 and the windings 3 and 5 are wound adjacent to each other. With such a configuration, when winding is performed, the windings 2 and 4 and the winding 3 are
Since 5 and 5 can be continuously wound with the same copper wire, the number of winding steps can be reduced.

Further, in the configuration of FIG. 3, the clamp 23 is fitted in the magnetic core 20 and is connected to the ground.
The effect in this case is shown in FIG. In FIG. 4, the horizontal axis represents frequency and the vertical axis represents noise output voltage of the noise filter.
A is the case where the magnetic core is not grounded, and B is the case where the magnetic core is grounded. It can be seen that when the magnetic core is grounded, it is greatly attenuated at high frequencies. By grounding the core in this way, the attenuation characteristics of the noise filter can be improved.

Further, in FIG. 3, the bobbin 8 is integrally formed, and the windings 2, 3, 4, and 5 are wound around the respective slits. By using such an integrally molded bobbin, the number of parts is small and the assembly is easy.

(Embodiment 3) A third embodiment of the present invention will be described below with reference to the drawings. FIG. 5 is a top view of a noise filter choke coil showing a third embodiment of the present invention. 5, windings 2 and 3 correspond to the windings 2 and 3 in FIG. The difference from the configuration of FIG. 1 is that the winding 3 is wound over two magnetic legs opposite to the winding 2, and the operation is exactly the same as that of FIG. With this configuration, the winding widths of the windings 2 and 3 are widened and the winding height is correspondingly reduced, so that the protrusion of the windings from the magnetic core is smaller than that in FIG.

[0024]

As described above, according to the present invention, since the composite choke coil in which the eye-shaped magnetic core having the four magnetic legs is wound and the magnetic core is grounded, it is thin and has the noise attenuation characteristic. It is possible to realize an excellent noise filter.

[Brief description of drawings]

FIG. 1 is a top view of a composite choke coil according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining the operation of the composite choke coil in the first embodiment.

FIG. 3 is a top view of a composite choke coil according to a second embodiment of the present invention.

FIG. 4 is a characteristic diagram of the second embodiment.

FIG. 5 is a top view of a composite choke coil according to a third embodiment of the present invention.

FIG. 6 is a circuit diagram showing a configuration of a two-stage noise filter.

FIG. 7 is a perspective view showing a conventional composite choke coil.

[Explanation of symbols]

 1a, 1b 4-leg magnetic core 2, 3, 4, 5 winding 6, 7 bobbin 20th-shaped magnetic core

Claims (3)

[Claims] 1. A first normal mode choke coil is formed by providing two windings having the same number of turns so as to straddle two inner magnetic legs of an eye-shaped magnetic core. A second normal mode choke coil is formed by providing two windings having the same number of turns so as to straddle the adjacent outer magnetic legs, and the first normal mode choke coil and the second normal mode choke coil are provided. A noise filter made by connecting in series. 2. The eye-shaped magnetic core is connected to ground.
The described noise filter. 3. The noise filter according to claim 1, wherein the bobbin of the first normal mode choke coil is integrally molded.