JPH08279724A - Common mode cholk circuit - Google Patents

Abstract

PURPOSE: To cancel a magnetic flux generated by an in-phase current inputted to a common mode cholk coil by winding the common mode cholk coil, a detection coil and an opposite phase coil around one core. CONSTITUTION: When an in-phase current 110 at a low frequency generated by an AC power source or the like flows to a common mode cholk coil 10, a magnetic flux 120 is generated by the in-phase current 110. Then, the magnetic flux 120 is detected by a detection coil 30 in a state quite before the magnetic saturation of a core member 40 and converted into a voltage, and an electric signal is sent to an LPF 50. The electric signal sent to the LPF 50 is sent to an operational amplifier 60 after only the high frequency component of AC line noise is cut. Concerning the electric signal sent to the operational amplifier 60, low-frequency noise is amplified while keeping its waveform as it is so that an opposite phase coil 35 is driven. Then, magnetic flux 130 of a phase opposite to that of the magnetic flux 120 is generated, and the magnetic flux 120 is suppressed by the magnetic flux 130.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to EMI (Electromagne
Noise filter circuits for tic interference, especially common mode choke circuits (hereinafter referred to as "CMC").
Circuit).

[0002]

2. Description of the Related Art When a power supply voltage is input to a device from a power supply line, a noise voltage other than a predetermined power supply voltage may enter the device and be input. Further, from the inside of the device, for example, in a switching power supply, noise at a high switching frequency or noise in the megahertz band is generated from a logic circuit of a personal computer as a load. A coil is mainly used as a power supply line filter for removing noise from the inside and outside of the power supply of such a device. For example, a common mode choke circuit (hereinafter referred to as "CMC" as disclosed in Japanese Patent Laid-Open No. 62-133812). Circuit ")
It has been known.

FIG. 4 shows a CMC circuit disclosed in Japanese Patent Laid-Open No. 62-133812, and FIG. 5 shows a conventional CMC circuit.
7 is a graph showing the relationship between input noise and output noise in the MC circuit.

In the conventional CMC circuit shown in FIG. 4, a CMC coil constructed by asymmetrically winding a coil 510 and a coil 520 around one core 540, a line 590 connecting the coil 510 to a circuit 660, and a coil 520. Is connected to the circuit 660 by a line 600,
Normally, a reciprocating current 670 and a reciprocating current 680 flow between the circuit 660 and the line 590 and the line 600 for exchanging signals or power.

When the above-mentioned CMC circuit is inserted in the AC100V power line, the line 590 and the line 60 are inserted.
Noise 570, which is a noise component input in the same phase from each 0, is suppressed by the coil 510 and the coil 520, and changes to a small noise (noise 580).

The relationship between the input noise which is the noise 570 and the output noise which is the noise 580 is as shown in FIG.

In FIG. 5, noise 58, which is output noise, is shown.
Since the magnitude of 0 is proportional to the magnitude of the noise 570 which is the input noise, the magnitude of the noise 570 is equal to the magnitude of the noise 580.
If increases gradually, it increases in proportion to it. However, if the magnitude of the noise 570 exceeds a certain value, the CMC
Since the coil core is saturated, the magnitude of the noise 580 is not proportional to the magnitude of the noise 570, but increases rapidly and the function as a line filter is lost. Therefore, the range of the voltage that effectively functions as a line filter is substantially determined by the saturation magnetic flux density of the core, and the larger the saturation magnetic flux density, the more effectively the large input noise acts.

Here, in the range where the noise 570 is small, that is, in the range where the CMC circuit effectively functions as a line filter, the noise 58 against the noise 570 is obtained.
The magnitude of 0 is related to the magnetic permeability of the core, and the higher the magnetic permeability, the smaller the noise 580.

Further, the line filter needs to function effectively not only in the low frequency region but also in the high frequency region of 1 MHz or higher. Therefore, it is necessary that the frequency characteristic of the magnetic permeability is also good.

As described above, the performance of the CMC circuit as a line filter depends on the characteristics of the core used for it, that is, the magnetic permeability, the saturation magnetic flux density, and the frequency characteristic of the magnetic permeability. It is desirable that both the density is high and the frequency characteristic of magnetic permeability and its magnetic field superposition characteristic are good.

Therefore, as a concrete measure against this, by using a large core such as an amorphous material having a large effective magnetic permeability and a good DC superimposition characteristic, the saturation magnetic flux density of the core material of the coil is increased to prevent EMI and the like. High frequency noise is removed.

[0012]

However, in the conventional CMC circuit as described above, a large core is used in order to make the line filter effectively function, so that it is limited to be adopted in a small system. However, if the core is downsized to suit a small system, the saturation magnetic flux density of the core material of the coil will decrease, and
There is a problem in that high frequency noise such as EMI to be removed cannot be removed in the MC circuit.

The present invention has been made in view of the above-mentioned problems of the prior art, and a line filter can be provided in a small system without reducing the magnetic flux density of the core material of the coil. It is an object to provide a CMC circuit that can effectively function.

[0014]

In order to achieve the above object, the present invention provides a common mode choke coil that is asymmetrically wound around one core material to reduce the noise level input to the circuit. A choke coil circuit, which detects a magnetic flux generated by an in-phase current input to the common mode choke coil and converts the magnetic flux into a voltage, and a low-pass filter circuit that cuts high-frequency components of an electric signal from the detection coil. And an operational amplifier for amplifying a low-frequency electric signal that is noise that has passed through the low-pass filter circuit, and a magnetic flux having a phase opposite to the magnetic flux generated by the common mode choke coil due to the electric signal amplified by the operational amplifier. And a common-mode choke coil for detecting the common-mode choke coil. A coil and the negative-phase coil is equal to or wound around the one core.

Further, the common mode choke coil is characterized in that it has a minimum size for reducing a noise level.

[0016]

In the present invention configured as described above, the detection coil detects the magnetic flux generated by the in-phase current input to the common mode choke coil and converts it into a voltage, and the converted electrical signal is converted into a low-pass filter and It is sent to the anti-phase coil via the operational amplifier, and the anti-phase coil generates a magnetic flux in the opposite direction to the magnetic flux generated in the common mode choke coil, so the magnetic flux generated by the in-phase current input to the common mode choke coil is canceled. To be done.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the CMC circuit of the present invention.

In the CMC circuit of this embodiment,
As shown in FIG. 1, the common mode choke coil 10 and the common mode choke coil 20 for removing common mode noise such as EMI input from the line 90 and the line 100 and the common mode current 110 input from the line 90 and the line 100 are used. A CMC coil is configured by winding three types of coils, a detection coil 30 for detecting the generated magnetic flux 120 and an anti-phase coil 35 for generating a magnetic flux 130 in the direction opposite to the magnetic flux 120, around one core 40. The coil has a low-pass filter 50 that cuts only high-frequency components from the output voltage of the detection coil 30.
And an operational amplifier 60 that amplifies the output voltage of the low-pass filter 50 and drives the anti-phase coil 35.

The line filter operation in the above CMC circuit will be described below.

In the above structure, when a low-frequency common-mode current 110 generated by an AC power source (not shown) or the like flows through the common-mode choke coil 10, a magnetic flux 120 is generated by the common-mode current 110.

Then, the magnetic flux 120 is detected by the detection coil 30 long before the core material 40 is magnetically saturated, converted into a voltage, and an electric signal is sent to the low-pass filter circuit 50.

The electric signal sent to the low-pass filter circuit 50 is sent to the operational amplifier 60 after only the high frequency component of the AC line noise is cut. Here, if the high-pass component is not cut by the low-pass filter circuit 50, even EMI noise is transmitted and the original function of the EMI filter is lost.

The electric signal sent to the operational amplifier 60 is amplified by low-frequency noise with its waveform unchanged, whereby
The reverse phase coil 35 is driven.

When the anti-phase coil 35 is driven, the magnetic flux 120
The magnetic flux 130 having a phase opposite to that of the magnetic flux 130 is generated, and the magnetic flux 130 suppresses the magnetic flux 120.

FIG. 2 is a diagram showing a DC superposition characteristic.

In the DC superposition characteristic curve shown in FIG. 2, when a CMC circuit having no common-mode current canceling function is used, the DC superposition characteristic becomes the position of point B 240 when the common-mode current is increased. Since it is included in the saturated region 220, the function as a line filter is lost. However, when the CMC circuit having the common-mode current canceling function is used as in the present embodiment, even if the common-mode current is increased, the magnetic flux due to the anti-phase coil increases accordingly, so the magnetic flux due to the common-mode current decreases, and the DC superposition characteristic Is located at the point A 230 and is not included in the magnetic flux saturation region 220, the CMC circuit effectively functions as a line filter.

FIG. 3 is a diagram showing the impedance characteristics of the conventional CMC circuit and the CMC circuit having the common-mode current canceling function in this embodiment.

As shown in FIG. 3, the CMC circuit having the common-mode current canceling function in this embodiment provides a high impedance characteristic and effectively functions as a line filter.

[0030]

Since the present invention is constructed as described above, it has the following effects.

According to the first aspect of the present invention, the detection coil for detecting the magnetic flux generated by the in-phase current input to the common mode choke coil and converting it into a voltage, and the high frequency component of the electric signal from the detection coil are cut. A low-pass filter circuit, an operational amplifier that amplifies an electric signal that has passed through the low-pass filter circuit, and a reverse phase that generates a magnetic flux having a phase opposite to the magnetic flux generated by the common mode choke coil by the electric signal amplified by the operational amplifier. Since the common mode choke coil, the detection coil and the anti-phase coil are wound around one core, it is possible to cancel the magnetic flux generated by the in-phase current input to the common mode choke coil. The magnetic saturation of the core material due to the increase of the electric current does not occur. As a result, it is not necessary to use a large core material with high DC superposition characteristics to increase the magnetic saturation resistance due to the common mode current, and the small size core material can increase the magnetic saturation resistance due to the common mode current.
Since impedance and inductance do not decrease,
It is effective for cost reduction and miniaturization.

According to the second aspect of the invention, the common mode choke coil has the minimum size for reducing the noise level, so that the same effect as that of the first aspect can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a CMC circuit of the present invention.

FIG. 2 is a diagram showing a DC superposition characteristic.

FIG. 3 is a diagram showing impedance characteristics of a conventional CMC circuit and a CMC circuit having a common mode current canceling function in the present embodiment.

FIG. 4 is a diagram showing a CMC circuit disclosed in JP-A-62-133812.

FIG. 5 is a graph showing the relationship between input noise and output noise in a conventional CMC circuit.

[Explanation of symbols]

 10, 20 Common mode choke coil 30 Detection coil 35 Reverse phase coil 40 Core material 50 Low pass filter circuit 60 Operational amplifier 90, 100 line 110 Common mode current (AC line noise) 120, 130 Magnetic flux 140 Power supply 150 Earth 160 circuit 220 Magnetic flux saturation region 230 A point 240 B point

Claims (2)

[Claims] 1. A common mode choke circuit for reducing a noise level input to a circuit by a set of common mode choke coils wound asymmetrically on one core material, the common mode choke coil being input to the common mode choke coil. The magnetic flux generated by the in-phase current is detected and converted into a voltage, a low-pass filter circuit that cuts high-frequency components of the electric signal from the detection coil, and low-frequency noise that is noise that has passed through the low-pass filter circuit. The common mode choke includes an operational amplifier for amplifying an electric signal, and an anti-phase coil for generating a magnetic flux having a phase opposite to a magnetic flux generated by the common mode choke coil by the electric signal amplified by the operational amplifier. The coil, the detection coil, and the antiphase coil are wound around one core material. Common mode choke circuit according to claim Rukoto. 2. The common mode choke circuit according to claim 1, wherein the common mode choke coil has a minimum size for reducing a noise level.