JPH0832394A - Noise filter - Google Patents

Abstract

PURPOSE:To provide the small-seized and inexpensive noise filter which effective ly suppresses the common mode electromagnetic noise in the low frequency band and the electromagnetic noise of the high frequency band, in the noise filter which suppresses the electromagnetic noise of the common mode developed across a pair of two lines and the ground. CONSTITUTION:A composite common mode choke coil 1 (1a and 1b) with at least two pairs of wirings wound around the magnetic core of one closed magnetic circuit and a capacitor 8 on both ends of a pair of wirings of the composite common mode choke coil 1. The noise filter is formed by connecting a line/earth capacitor 9 between the line and an earth terminal 10 on the input and output sides of a composite common mode choke coil 1 and line-to-line capacitors 6a and 6b between lines.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise filter mounted on electronic equipment to suppress electromagnetic noise.

[0002]

2. Description of the Related Art In a conventional common mode choke coil forming a noise filter, a round copper wire is wound around a toroidal core manually or by using a winding machine. In the conventional noise filter of this kind, one noise is generated by connecting a common mode choke coil having two windings in a common mode to a toroidal core of a closed magnetic circuit having a high relative magnetic permeability characteristic, a capacitor and a resistor. Forming a filter. On the other hand, when a noise suppression effect is required up to the low frequency range, noise filters that require a high attenuation characteristic in the low frequency range include a noise filter incorporating a common mode choke coil with a large inductance value and a high frequency range. Therefore, it is necessary to combine and form a plurality of noise filters having high attenuation characteristics, and the shape becomes large. On the other hand, since winding is applied to each of the two or more toroidal cores and two or more common mode choke coils are incorporated into the circuit, the material cost becomes high, the assembling workability is poor, and the number of assembling steps is large. It was an extremely expensive noise filter.

[0003]

In order to eliminate these drawbacks, the present invention has a large attenuation characteristic in the low frequency range, is small in size, is inexpensive, and is excellent in productivity. An object of the present invention is to provide a noise filter that is effective in suppressing the noise.

[0004]

According to the present invention, a rectangular copper wire is wound around a rectangular core of a closed magnetic circuit magnetic body formed by combining U-shaped cores whose opening sides are opposed to each other and fitted in a rectangular shape. Two or more pairs of cylindrical windings are used so that magnetic fields created by currents flowing in opposite directions in the windings cancel each other in the opposing magnetic legs of the rectangular core. On the other hand, for a current caused by so-called common mode electromagnetic noise flowing in the same direction, at least two common mode choke coils wound so as to generate high inductance are formed in one closed magnetic circuit. Use as a coil. The windings wound around the magnetic legs of the respective rectangular cores of the two or more common mode coils of the composite common mode choke coil are connected in series. A capacitor is connected in parallel to the choke coil in one common mode choke coil to form a parallel resonance circuit with the capacitor. In a specific frequency band in the low frequency range, the one common mode choke coil is operated so as to have high impedance, and the other common mode choke coil is
It is designed to have a high impedance in the entire frequency band of noise generation until the self-resonance due to the stray capacitance between the windings occurs. Further, a capacitor is connected between two wires in a π type with respect to the composite common mode choke coil described above. Also line-
By connecting a capacitor between the grounds to form an inverse L-type filter and forming a low-pass filter type circuit, it has a high attenuation characteristic for a specific frequency band of low frequency, and has a high attenuation characteristic up to a high frequency range. Suppresses electromagnetic noise, is inexpensive,
And construct a noise filter that can be realized in a small size. The noise filter of the present invention can be installed by reversing it before and after the connection of the capacitor connected to the composite common mode choke coil. Further, depending on the frequency band of electromagnetic noise, each common mode choke coil of the composite common mode choke coil for suppressing electromagnetic noise is a common mode choke coil having a different inductance. Further, by changing the constant of the capacitor, it is possible to arbitrarily change the attenuation characteristic of the frequency band in accordance with the noise generating frequency component.

That is, the present invention provides a composite common mode choke coil in which at least two pairs of common mode windings are provided on a closed magnetic circuit core having high relative magnetic permeability characteristics, and at least one pair of commons of the composite common mode choke coil. A noise filter comprising a capacitor connected to both ends of a mode winding, a line capacitor connected to the input side and the output side of the composite common mode choke coil, and a line-ground capacitor. is there.

[0006]

A rectangular core in which opening sides of U-shaped cores are butted and combined with each other, and two windings wound around one magnetic leg of two pairs of common mode choke coils formed in the rectangular core are connected in series. , A capacitor connected in parallel to one common mode choke coil wound around the opposite magnetic legs of a rectangular core so as to generate parallel resonance in the low frequency range is a low frequency component electromagnetic wave flowing in the common mode choke coil in the low frequency range. Try to create a high impedance to noise. On the other hand, the windings wound around the facing magnetic legs of at least two pairs of common mode chokes formed on the magnetic legs of the rectangular core are connected in series to the input side and the output side of the composite common mode choke coil. Connect a capacitor between two lines. Moreover, since the capacitor is connected between the two lines and the ground, the compound common mode is excluded except the parallel resonance frequency range generated by the capacitor connected in parallel to one common mode choke that has a high impedance to the current flowing through the line. The inductance of the choke coil, the capacitor connected between the input side and the output side, the capacitor between each of the two lines and the ground side, the normal mode electromagnetic noise between the two lines, and And a noise filter that suppresses common mode electromagnetic noise generated between one line and the ground side. Further, since the noise filter is not formed by combining two noise filters having different attenuation frequency ranges in which capacitors are respectively combined with two common mode choke coils, the number of capacitors forming the noise filter is reduced, and the noise filter The overall size and the number of assembling steps for assembling the parts are smaller than in the conventional case, and a small and inexpensive noise filter having a large attenuation characteristic in the low frequency region and the high frequency region can be configured.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the noise filter of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of a circuit which constitutes the noise filter of the present invention. In the noise filter of the present invention, the composite common mode choke coil 1 is shown in FIG.
As shown in FIG. 4, the cylindrical winding 5 wound with the rectangular wire shown in FIG. 4A is incorporated in the core cap 4 that insulates between the windings and the U-shaped core 3. The opening side of the U-shaped core 3 is inserted into the core insertion hole 4a, and the two U-shaped cores 3 are abutted and combined with each other. The cylindrical winding 5a and the cylindrical winding 5b incorporated in the core cap 4 are shown in FIG.
The one common mode choke coil 1a, the cylindrical winding 5c and the cylindrical winding 5d form another common mode choke coil 1b. In the present invention, the capacitor 8 is connected in parallel to the common mode choke coil 1a of the composite common mode choke coil 1 , and the low frequency specific frequency is determined by the inductances L ₁ and L _{2 of} the common mode choke coil 1a and the capacitance Cp of the capacitor 8. In the above-mentioned specific frequency range, a high impedance is formed with respect to a common mode voltage flowing in parallel to the two lines. Further, the composite common mode choke coil 1 having a high impedance characteristic in the low frequency region, and the line-to-line capacitors (C _X ) 6a and 6b on the input side and the output side of the composite common mode choke coil.
And a line-to-ground capacitor 9 (C _Y ) between the line and the ground terminal 10 constitute a π-type noise filter circuit, and a high amount of attenuation can be obtained at a specific low frequency. That value of inductance by connecting a capacitor 8 at both ends of the common mode choke coil 1a of L _1, L _2, parallel in the low frequency range by the capacitance Cp of the inductance L _1, L ₂ and the capacitor 8 of the common mode choke coil Resonance and high impedance in series with the line,
A π-type filter circuit for normal mode noise is formed between the line capacitors (C _X ) 6a and 6b, and a π-type filter circuit for common mode noise is formed between the line-ground capacitor (C _Y ) 9. Form. Since impedance is formed over the entire noise generation band up to the self-resonant frequency of L ₃ and L ₄ of the other common mode choke coil 1b, the impedance and the line capacitor (C _X ) 6
Attenuation can be obtained in the entire noise generation band by the π-type filtering circuit with the capacitive low impedance of the capacitors a and 6b and the line-to-ground capacitor (C _Y ) 9.

The amount of attenuation of this noise filter is the above two π
Since it is a combination of the attenuation amounts of the type filter circuit, it is possible to provide an inexpensive and small noise filter having the characteristics of combining the high attenuation amount at low frequencies and the good attenuation amount in the entire area of the common mode choke coil. . Further, the center frequency and the band of the low-frequency high attenuation also have inductance values L ₁ and L _{2 of one} common mode choke coil 1a of the composite common mode choke coil and a capacitor (C _P connected in parallel to the common mode choke coil). The resonance frequency in the low frequency range can be arbitrarily set by changing the element value of 8).

Although the common mode noise has been described above, the leakage inductance of the composite common mode choke coil 1 and the line capacitors 6a and 6b with respect to the normal mode noise cause the normal mode noise in the same manner as the common mode noise. A π-type filter circuit is formed for noise.

FIG. 2 shows a mounting diagram when the filtering circuit constituting the noise filter of the present invention shown in FIG. 1 is mounted on the printed board 11. As shown in FIG. 4, the composite common mode choke coil 1 has two U-shaped cores 3 abutting each other on their opening sides so as to form a closed magnetic path, and the U-shaped cores 3 are inserted and fitted into the core insertion holes 4a of the core cap 4. The rectangular copper wire 5 is assembled and formed on the core cap 4. Connecting the capacitor 8 and the line-to-line capacitors 6a and 6b, the line-to-ground capacitor 9 and the resistor 7 for causing parallel resonance in parallel to one common mode choke coil of the composite common mode choke coil, on the printed circuit board 11. To form a noise filter circuit. In FIG. 2, the external connection terminal 2 and the ground terminal 10 of the noise filter are also connected to the noise filter circuit on the printed circuit board.

FIG. 3 shows the attenuation characteristic with respect to the frequency of the noise filter in one embodiment of the noise filter of the present invention.

In the attenuation characteristics of the noise filter of FIG. 3, the common mode choke coils 1a and 1b constituting the composite common mode choke coil 1 of FIG. 1 have an inductance value of 1.8 mH, and the common mode choke coil 1a is wound. The value of the capacitor (C _P ) 8 connected to both ends of the lines 5a and 5b is 1000 PF, the value of the line-to-ground capacitor (C _Y ) 9 is 4700 PF, the line capacitor 6a,
The value of 6b is 0.22μF, and the resistance 7
Is a discharge resistor for discharging a DC voltage between the lines. Also, the connection terminals of the noise filter for measuring the attenuation characteristics are measured by terminating with a resistance of 50Ω on both the input side and the output side. In the above-mentioned embodiment, each common mode choke coil 1 of the composite common mode choke coil 1 is used.
The values of a and 1b are set to the same value at 1.8 mH,
The inductance value may be changed by changing the number of turns of the cylindrical winding of each common mode choke coil, and the capacitance values of the line capacitors 6a and 6b, the line-ground capacitor 9 may be changed.
It goes without saying that the capacity value of can be appropriately selected in addition to the above numerical values.

In the composite common mode choke coil of the present invention, an example is shown in which a rectangular core is used in which two U-shaped cores are butted against each other at the opening side. However, a ring having a high relative magnetic permeability characteristic without an air gap is used. A noise filter in which a composite common mode choke is formed by forming at least two pairs of common mode chokes in a closed magnetic circuit core, and at least one pair of common mode chokes is connected in parallel with a capacitor that causes parallel resonance with the common mode choke coil at low frequencies. It is natural that

[0015]

As described above, the number of parts constituting the noise filter is smaller than that of the conventional one, and it is small and inexpensive, and has a better attenuation characteristic than the conventional noise filter against electromagnetic noise in the low frequency range. An excellent noise filter can now be provided.

[Brief description of drawings]

FIG. 1 is a filtering circuit diagram showing an embodiment of a noise filter according to the present invention.

FIG. 2 is a plan view showing an embodiment of mounting a noise filter on a substrate according to the present invention.

FIG. 3 is a characteristic diagram showing an attenuation characteristic of an embodiment of a noise filter according to the present invention.

FIG. 4 is a perspective view showing the configuration of a composite common mode choke coil that constitutes the noise filter according to the present invention. FIG.
FIG. 4A is an external perspective view showing a tubular winding, and FIG. 4B is an exploded perspective view of a composite common mode choke coil.

[Explanation of symbols] 1 composite common mode choke coil 1a, 1b common mode choke coil 2 external connection terminal 3 U-shaped core 4 core cap 4a core insertion hole 5, 5a, 5b, 5c, 5d cylindrical winding 6a, 6b wire Capacitor 7 Resistance (Discharge resistance) 8 Capacitor 9 Wire-to-ground capacitor 10 Ground terminal 11 Printed circuit board

Claims (1)

[Claims] 1. A composite common mode choke coil comprising at least two pairs of common mode windings on a closed magnetic circuit core having high relative magnetic permeability characteristics, and at least one pair of common mode windings of the composite common mode choke coil. A noise filter comprising: a capacitor connected to both ends of the capacitor; a line-to-line capacitor connected to the input side and the output side of the composite common mode choke coil; and a line-to-ground capacitor.