JPS61230417A - Noise filter - Google Patents

Abstract

PURPOSE:To obtain a large attenuation over a wide band by connecting two choke coils in series and arranging the choke coils having a core with a small permeability to a position being noise generating source eliminated by a noise filter. CONSTITUTION:The choke coil using a core having a small permeability in the choke coils is arranged to the side of noise generation source eliminated by a noise filter. The attenuation of the noise filter at a high frequency over the HF band depends on the stray capacitance between the input and output of the noise filter, the attenuation is reduced as the stray capacitance is large and the attenuation depending on the impedance of the coil main body is not obtained. One of factors deciding the stray capacitance between the input and output is a distance between the input and output and the reduction in the attenuation is prevented by parting the distance between the input and output as much as possible. Thus, a high frequency noise is attenuated immediately at the input side by arranging the choke coil using a core having a small permeability playing a role of the attenuation effect to the noise input so as to prevent the high frequency noise from being coupled via the stray capacitance between the input and output.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a noise filter that prevents noise from entering and leaking.

(Prior Art) A circuit diagram of a conventional general noise filter is shown in FIG. 2. L3 is a common mode choke coil, C1 is a capacitor for normal mode noise reduction, and Cl
l C3 is a common mode noise reduction capacitor.

Conventionally, for common mode noise, 0.1 to 40 M
In order to obtain the desired amount of attenuation over a wide band such as Hz, capacitors C, , C, between the line and ground are required together with the choke coil L3.

(Problem to be solved by the invention) As mentioned above, in order to attenuate common mode noise, conventional noise filters require a capacitor between the line and ground.However, this capacitor does not allow leakage current It was also the cause of the occurrence of This leakage current poses a risk of electric shock and the like, and is particularly problematic in medical equipment. In some devices, the maximum value of this leakage current is specified.

In view of the above, the present invention provides a noise filter that can obtain sufficient attenuation for common mode noise over a wide band using only a choke coil without using a line-to-ground capacitor.

(Means for Solving the Problems) The present invention uses two choke coils, the magnetic cores of the choke coils each have a different frequency characteristic of magnetic permeability, and the two choke coils are connected in series. A choke coil using a core with low magnetic permeability is placed on the side of the source of the noise to be removed by the noise filter.

(Function) The amount of attenuation at high frequencies in the HF band of the noise filter depends on the stray capacitance between the input and output of the noise filter, and the larger the stray capacitance, the lower the attenuation characteristics. One of the factors that determines this stray capacitance between input and output that cannot be obtained is the distance between input and output. In other words, by increasing the distance between input and output as much as possible,
It is possible to prevent a decrease in the amount of attenuation.

Therefore, for high frequency noise above the IF band.

By placing a choke coil with a core with low magnetic permeability that exhibits an attenuation effect on the noise input side, high-frequency noise is immediately attenuated on the input side, and high-frequency noise is transmitted through stray capacitance between input and output. This prevents them from merging.

(Embodiment) Embodiment FIG. 1 shows a circuit diagram of an embodiment according to the present invention. In this embodiment, a capacitor for reducing normal mode noise is not shown, but normal mode noise reduction is the same as the conventional one, and a capacitor may be inserted between lines as appropriate. In the embodiment shown in Fig. 1, coil A with a core of μ=1500 is used for L, and L
Coil B using a core with μ=7000 was used for No. 2. At this time, the noise that is mainly removed by this noise filter is input to this noise filter in the direction of arrow N.

Attenuation of common mode noise according to an embodiment of the present invention in which choke coil A using a core with low magnetic permeability is placed on the noise input side, and choke coil B using a core with high magnetic permeability is placed on the output side. The characteristics are shown in the 4111th graph C.

Comparative Example The circuit diagram shown in Figure 1 uses coil B for input side L2, coil A for output side L2, and places choke coil B using a core with high magnetic permeability on the noise input side. Graph d in FIG. 4 shows the attenuation characteristics against common mode noise of a comparative example in which choke coil A using a core with low magnetic permeability is arranged on the output side.

Conventional Example 1 Graph a in FIG. 5 shows the attenuation characteristic of only coil A against common mode noise.

Conventional Example 2 Graph b in FIG. 5 shows the attenuation characteristic of only coil B against common mode noise.

It is clear from these Examples, Comparative Examples, and Conventional Examples that the noise filter according to the present invention is able to obtain a sufficient amount of attenuation over a wide band with respect to common mode noise.

(Effects of the Invention) As described above, the present invention provides a noise filter that can obtain a large amount of attenuation over a wide band without using a line-to-ground capacitor, and also prevents leakage current. It is extremely useful for industry.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment according to the present invention, and FIG.
3 is a circuit diagram of a conventional noise filter, FIG. 3 is a diagram showing the attenuation characteristics of coil A and coil B against common mode noise, and FIG. 4 is a diagram showing an example of the present invention and a comparative example. This is the attenuation characteristic for common mode noise. Hani no Kise 2nd page '$3 side shoulder η Ukuden CMHz3 'j44 diagram

Claims (1)

[Claims] A noise filter in which two choke coils are used, the two choke coils are connected in series, the choke coils have cores having different frequency characteristics of magnetic permeability, and the choke coils are connected in series. 1. A noise filter characterized in that a choke coil using a core with low magnetic flux is arranged on the side of the source of the noise to be removed by the noise filter.