JP2708008B2 - Common mode choke circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an EMI (Electromagne
tic Interference) noise filter circuit, especially the common mode choke circuit (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. Also, from inside the device, for example, in a switching power supply, noise at a high frequency of a switching frequency or noise in a megahertz band is generated from a logic circuit of a personal computer as a load. A coil is mainly used as a power line filter for removing noise from inside and outside of a power supply of such a device. For example, a common mode choke circuit (hereinafter referred to as "CMC") disclosed in Japanese Patent Application Laid-Open No. 62-133812. Circuit)
It has been known.

FIG. 4 is a diagram showing a CMC circuit disclosed in Japanese Patent Application Laid-Open No. Sho 62-133812, and FIG.
4 is a graph showing a relationship between input noise and output noise in an MC circuit.

The conventional CMC circuit shown in FIG. 4 includes a CMC coil formed 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. And a line 600 connected to the circuit 660.
Normally, a round-trip current 670 and a round-trip current 680 flow between the circuit 660 and the lines 590 and 600 to transfer signals or power.

When the above-described CMC circuit is inserted into a power supply line of AC100V, the line 590 and the line 60
The noise 570, which is a noise component input in the same phase from each of 0, is suppressed by the coils 510 and 520, and changes to small noise (noise 580).

FIG. 5 shows the relationship between input noise 570 and output noise 580.

[0007] In FIG.
Since the magnitude of 0 is proportional to the magnitude of noise 570 which is input noise, the magnitude of noise 570 is
Gradually increases in proportion to it. However, when the magnitude of the noise 570 exceeds a certain value, CMC
Since the core of the coil is saturated, the magnitude of the noise 580 increases rapidly without being proportional to the magnitude of the noise 570, and the function as a line filter is lost. For this reason, 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 effective the input noise becomes.

Here, in a range where the noise 570 is small, that is, in a range where the CMC circuit effectively functions as a line filter, the noise 58 with respect to the noise 570 is reduced.
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 a low frequency region but also in a high frequency region of 1 MHz or more, and therefore, it is necessary that the frequency characteristics of the magnetic permeability be good.

As described above, the performance of a CMC circuit as a line filter depends on the characteristics of the core used therein, ie, the magnetic permeability, the saturation magnetic flux density, and the frequency characteristics of the magnetic permeability. Desirably, both the densities are large and the frequency characteristics of the magnetic permeability and the magnetic field superposition characteristics thereof are good.

Therefore, as a specific countermeasure, the use of a large core made of amorphous or the like having a large effective magnetic permeability and good DC superimposition characteristics increases the saturation magnetic flux density of the core material of the coil, thereby reducing the EMI and the like. It removes high frequency noise.

[0012]

However, in the conventional CMC circuit as described above, a large core is used in order to make the line filter function effectively, so that it cannot be used in a small system. If the core is reduced in size in accordance with a small system, the saturation magnetic flux density of the core material of the coil decreases, and the C
There is a problem that high frequency noise such as EMI to be removed in the MC circuit cannot be removed.

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

[0014]

According to the present invention, there is provided a common mode choke for reducing a noise level input to a circuit by a set of common mode choke coils wound asymmetrically around one core material. A coil circuit, which detects a magnetic flux generated by a common-mode current input to the common mode choke coil and converts the magnetic flux into a voltage, and a low-pass filter circuit that cuts a high-frequency component of an electric signal from the detection coil. An operational amplifier that amplifies a low-frequency electric signal that is noise that has passed through the low-pass filter circuit; and an electric signal amplified by the operational amplifier, which generates a magnetic flux having a phase opposite to that of a magnetic flux generated by the common mode choke coil. A negative-phase coil for generating the common mode choke coil and the detection coil. A coil and the negative-phase coil is equal to or wound around the one core.

[0015]

[0016]

According to the present invention, the magnetic flux generated by the common-mode current input to the common mode choke coil is detected by the detection coil and converted into a voltage. It is sent to the negative-phase coil via the operational amplifier, and the negative-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 common-mode current input to the common-mode choke coil is canceled Is done.

[0017]

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

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

In the CMC circuit of this embodiment,
As shown in FIG. 1, a common mode choke coil 10 and a common mode choke coil 20 for removing common mode noise such as EMI input from the lines 90 and 100 and a common mode current 110 input from the lines 90 and 100 are used. A detection coil 30 for detecting the generated magnetic flux 120 and a reverse coil 35 for generating a magnetic flux 130 in the opposite direction to the magnetic flux 120 are wound around one core 40 to form a CMC coil. The coil includes 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 negative-phase coil 35.

Hereinafter, a line filter operation in the above-described CMC circuit will be described.

In the above configuration, when a low-frequency common-mode current 110 generated by an AC power supply (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.

The magnetic flux 120 is detected by the detection coil 30 and converted into a voltage before the core member 40 is magnetically saturated, 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 off. Here, if the high-frequency component is not cut by the low-pass filter circuit 50, EMI noise is passed and the original function of the EMI filter is lost.

The electric signal sent to the operational amplifier 60 amplifies low-frequency noise with its waveform as it is.
The negative phase coil 35 is driven.

When the reverse phase coil 35 is driven, the magnetic flux 120
A 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 superimposition characteristic.

In the DC superimposition characteristic curve shown in FIG. 2, when a CMC circuit having no common-mode current canceling function is used, as the common-mode current is increased, the DC superposition characteristic becomes the position of point B 240 and the magnetic flux Since it is included in the saturation region 220, the function as a line filter is lost. However, when a CMC circuit having a 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 negative-phase coil increases. Becomes the position of the point A 230 and is not included in the magnetic flux saturation region 220, so that the CMC circuit effectively functions as a line filter.

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.

As shown in FIG. 3, the CMC circuit having the in-phase current canceling function in this embodiment has high impedance characteristics and functions effectively 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 detects the magnetic flux generated by the common-mode current input to the common mode choke coil and converts it into a voltage, and cuts the high frequency component of the electric signal from the detection coil. A low-pass filter circuit, an operational amplifier that amplifies the electric signal that has passed through the low-pass filter circuit, and an opposite phase that generates a magnetic flux having a phase opposite to that of the magnetic flux generated by the common mode choke coil by the electric signal amplified by the operational amplifier. A common mode choke coil, a detection coil, and a negative phase coil are wound around a single core, so that a magnetic flux generated by a common mode current input to the common mode choke coil can be canceled. Magnetic saturation of the core material due to an increase in current does not occur. As a result, it is not necessary to use a large core material having a high DC superimposition characteristic in order to increase the magnetic saturation resistance due to the common-mode current, and the magnetic saturation resistance due to the common-mode current can be increased with a small-sized core material.
Because both impedance and inductance do not decrease,
It is effective for cost reduction and miniaturization.

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

[Brief description of the drawings]

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

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

FIG. 3 is a diagram illustrating 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 Japanese Patent Application Laid-Open No. 62-133812.

FIG. 5 is a graph showing a 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 ground 160 circuit 220 magnetic flux saturation area 230 Point A 240 Point B

Claims (1)

(57) [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 around one core material, wherein the common mode choke coil is input to the common mode choke coil. A detection coil that detects a magnetic flux generated by the in-phase current and converts it into a voltage; a low-pass filter circuit that cuts a high-frequency component of an electric signal from the detection coil; and low-frequency electricity that is noise that has passed through the low-pass filter circuit. An operational amplifier that amplifies a signal; and an opposite-phase coil that generates a magnetic flux having a phase opposite to that of a magnetic flux generated by the common-mode choke coil, based on the electric signal amplified by the operational amplifier. And the detection coil and the negative phase coil are wound around one core material. Common mode choke circuit according to claim Rukoto.