JPS624310A - Noise filter - Google Patents

Abstract

PURPOSE:To increase the noise level reduction effect and improve temperature characteristics by employing Fe radical amorphous alloy with a saturated magnetostriction (lambdas) of 7X10<-6=lambdas<=15X10<-6> as a core material. CONSTITUTION:A core obtained by winding or laminating Fe radical amorphous alloy with a saturated magnetostriction (lambdas) of 7X10<-6=lambdas<=15X10<-6> is employed. The Fe radical amorphous alloy is expressed by the attached formula, wherein M represents at least one of Ti, V, Cr, Mn... and Y means at least one of Si, B, P, C and Ge. In order to obtain the range of lambdas of 7X10<-6=lambdas<=15X10<-6>, (a) which shows the rate of substitution of Fe by M is selected to be in the range of 0.04<=a<=0.14. With the constitution, the noise level reduction effect can be increased and temperature characteristics can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a noise filter using an Fe-based amorphous alloy.

[Technical background of the invention and its problems]

When power supply voltage is input to a device from a power line, noise voltage other than the predetermined power supply voltage may enter the device and be input. Furthermore, in the case of a switching power supply, noise in the MHz range is generated from harmonics of the switching frequency or from the logic circuit of the personal computer, which is a load. Coils are mainly used as power line filters for such noise removal (to prevent intrusion from outside the power supply and to prevent noise within the power supply from being emitted to the outside).

FIG. 1 is an example of a power line filter circuit using a choke coil. The choke coil 1 has a pair of windings 3m and 3b around the magnetic core 2 so that the magnetic flux due to the reciprocating current is canceled out.
with a capacitor 4as between the windings JasJb
4bs4c is connected, and the connection point of capacitor 4b*4a is grounded.

When this power line filter is inserted into the AClooV power line, the relationship between the noise input voltage and the noise output voltage will be as shown in FIG. Here, in a range where the noise input voltage is small, the magnitude of the noise output voltage with respect to the noise input voltage is related to the magnetic permeability of the magnetic core, and the larger the magnetic permeability, the smaller the noise output voltage becomes. Furthermore, when the noise input voltage exceeds a certain value, the magnetic core of the power line filter becomes saturated, so the noise output voltage increases rapidly and the function as a power line filter is lost. For this reason, the voltage range that effectively functions as a power line filter is determined by the saturation magnetic flux density of the magnetic core, and the higher the saturation magnetic flux density, the more effectively the filter acts on a large noise input voltage. Furthermore, the power line filter needs to function effectively not only in the low frequency range but also in the high frequency range of I MHz or higher, and for this reason, it is necessary that the frequency characteristics of magnetic permeability are also good.

As mentioned above, the performance of a power line filter is determined by the characteristics of the magnetic core used in it, such as magnetic permeability, saturation magnetic flux density,
It depends on the frequency characteristics of magnetic permeability, and it is desirable that both the magnetic permeability and the saturation magnetic flux density of the magnetic core are large, and the frequency characteristics of magnetic permeability are also good.

Conventionally, ferrite magnetic cores, silicon steel magnetic cores, etc. have been used as this magnetic core. Among these, the ferrite magnetic core has a relatively high magnetic permeability and a good frequency characteristic of magnetic permeability, but the saturation magnetic flux density is as small as about 4 kG, and it cannot work effectively against a large noise input voltage. In addition, ferrite has poor magnetic permeability temperature characteristics, and it has been desired to improve the temperature characteristics. On the other hand, although a silicon steel magnetic core has a high saturation magnetic flux density, its magnetic permeability in a high frequency region is low, and it cannot function effectively in this region.

Furthermore, recently, magnetic cores made of amorphous alloys have been studied. However, in the case of an Fs-based amorphous alloy with a high saturation magnetic flux density, it is not possible to obtain a large magnetic permeability, and this is not necessarily sufficient for noise reduction.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned drawbacks, and an object of the present invention is to provide a noise filter that is effective in reducing the noise level and has excellent temperature characteristics.

[Summary of the invention]

The noise filter of the present invention has a saturation magnetostriction (λ, ) of 7X
The present invention is characterized in that an Fe-based amorphous alloy of 10""-6≦λS≦15X10-' is used as the magnetic core.

In the present invention, the saturation magnetostriction of the Fe-based amorphous alloy is limited to the above range for the following reasons. In other words, if λ8 is less than 7X10'', both the saturation magnetic flux density and Curie temperature will be low, and the temperature characteristics as a noise filter will deteriorate.Furthermore, the magnetic flux will easily become saturated against high voltage pulse noise, making it ineffective. On the other hand,
This is because when λ3 exceeds 15X10, high magnetic permeability cannot be obtained due to magnetic anisotropy caused by saturation magnetostriction, and the frequency characteristics of magnetic permeability are also not good, so it is not effective in reducing high frequency noise at the switching frequency. . A more preferable range of saturation magnetostriction λ8 is 9×10 −6≦λS≦13X1
It is 0. Note that λ8=7X10. 15X10
The saturation magnetic flux densities of the Fe-based amorphous alloys are approximately 9 kG and 12 kG, respectively.

In Fe-based amorphous alloys, a part of Fe is replaced with, for example, C
It is known that substitution with a transition metal such as r+Nl+Nb lowers the saturation magnetostriction. Such Fe-based amorphous alloys generally have the following formula % (where M: Ti, V, Cr, Mn, Ni,
Co, Cu, Zr, Nb.

At least one member selected from Mo, Hf, Ta, Rh, Pd, Ru, W, and rare earth elements; Y: at least one member selected from St, B, P, C, and G. In particular, the element M is Cr.

Ni, Nb, and Me are preferred.

In the above formula, M generally has the effect of increasing the ability to form an amorphous state and lowering the saturation magnetostriction of the amorphous alloy. In particular, Nb, Mo, Ta, and W also have the effect of increasing the crystallization temperature of the amorphous alloy. Also, Cr, Pd
, Rh, and Ni have the effect of improving the corrosion resistance of the amorphous alloy. In order to obtain a value in the range of 7 x 10-'≦λ1≦15 x 10-6 as the saturation magnetostriction of the amorphous alloy, the amount of substitution by F・OM is
This can be realized by setting tl-0,04≦a≦0.14.

On the other hand, Y is an element added to make the alloy amorphous. Y is preferably a combination of Si and B from the viewpoint of thermal stability and resistance to embrittlement. b, which indicates the amount of Y added, is limited within the range that can make the alloy amorphous, and is 12≦b≦30.

[Embodiments of the invention]

The present invention will be explained in detail below.

First, amorphous alloy ribbons of Examples 1 to 12 and Comparative Examples 1 to 4 having the compositions shown in the table below were produced by a single roll method. The saturation magnetostriction of these ribbons is shown in the table below. Next, using these thin strips, each has an outer diameter of 18
Molded into a toroidal core with a 21111% inner diameter of 12 mm.

After each core obtained was subjected to optimal heat treatment, it was placed in a case and rolled.

These cores were used as an inductance element in a line filter of a switching power supply with a switching frequency of 40 kHz, and the noise level reduction effect was investigated compared to a case where no inductance element was used. Furthermore, the temperature characteristics were investigated by comparing the noise level at room temperature and the noise level at 120°C. These results are also listed in the table below.

As is clear from the above table, the cores of Comparative Examples 1 and 2 have a saturation magnetostriction of more than 15×10 2 , so the noise level reduction effect is small. In addition, the core of Comparative Example 3.4 has a saturation magnetostriction of less than 7 x 10"-6, so the temperature characteristics are poor. On the other hand, the core of Comparative Example 3.4 has a saturation magnetostriction of less than 7 x 10"-6, so the temperature characteristics are poor. When the Fs-based amorphous alloy was used, excellent values were obtained for both the noise level reduction effect and the temperature characteristics.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide a noise filter that has a large noise level reduction effect and also has excellent temperature characteristics, and its industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a power line filter circuit using a choke coil, and FIG. 2 is a characteristic diagram showing the relationship between noise input voltage and noise output voltage of the power line filter circuit. Figure 1 Figure 2

Claims (1)

[Claims] Fe with saturation magnetostriction (λ_S) of 7×10^-^6≦λ_S≦15×10^-^6
A noise filter characterized by using a magnetic core obtained by winding or laminating a base amorphous alloy.