JPH04337611A - Iron group alloy toroidal core with superior magnetic characteristics - Google Patents

Abstract

PURPOSE:To provide a toroidal core that improves the impulse attenuation characteristics and noise attenuation characteristics utilizing characteristics of iron group magnetic material. CONSTITUTION:Provided is a toroidal core made of iron group alloy, with inside/outside diameter ratio (r1/r2) being 0.78+ or -0.1. The inside/outside diameter ratio is substantially different as compared with 0.5-0.6 of the general value of ferrite. With the core whose inside diameter is 20mm taken as a reference, it is possible to expect the increment of inductance in the case of inside diameter of 30mm compared with a conventional method, with outside diameter being smaller by 23%.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the shape of an iron-based alloy toroidal core having excellent impedance characteristics for use in noise filters such as common mode chokes used in switching power supplies and the like.

0002

2. Description of the Related Art Currently, various common mode chokes are widely used as EMC components related to switching power supplies. Conventionally, ferrite has been used as a material for this common mode choke due to its cost or stable impedance characteristics up to a high frequency range. However, the recent E
With the trend towards lower frequencies in MC regulations, improvements in impedance characteristics in the low frequency range have come into question.

A conventional ferrite toroidal core is shown in FIG.
The inner/outer diameter ratio defined by r1/r2 is 0.5 to 0.
It is used in a range of 6. This means that when the copper windings wound around the core are uniformly distributed along the inner circumference of the core, that is, when the windings are wound approximately in a single layer, the optimum diameter ratio, that is, the impedance required to remove noise, is the maximum. It is designed to be. This core diameter ratio was appropriate for fired oxide materials with low saturation magnetic flux density, such as ferrite materials, but iron-based alloy magnetic materials with high saturation magnetic flux density that have been newly developed in recent years Materials were not considered.

0004

Problem to be Solved by the Invention The problem to be solved by the present invention is how to improve the noise attenuation characteristics, especially in the low frequency range, while satisfying the impulse attenuation characteristics by making use of the characteristics of the iron-based alloy magnetic material. The question is whether to provide a toroidal core.

[0005]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides an iron-based alloy toroidal core having an inner/outer diameter ratio of 0.78±0.1. In other words, in order to solve the above-mentioned problem, the present inventors prototyped toroidal cores of various shape ratios using iron-based alloys and conducted evaluation studies. It has been found that a ratio completely different from the inside/outside ratio of 0.5 to 0.6 is optimal. The present invention will be specifically explained below.

[0006]

[Function] The iron-based alloy toroidal core is one with an Fe content of 50% (atomic %) or more, for example, Fe8.
5-94 Si6-15 atomic% crystal alloy, Fe73.5
Si13.5B9Cu1Nb3 atomic% crystal alloy, Fe7
2Co10Mo2B12Si4 amorphous alloy, Fe80
．． 5Si6.5B12C1 amorphous alloy, Fe79Si8
B13 amorphous alloy, Fe79Si8B13 amorphous alloy,
Fe78Cr6B12C4 amorphous alloy, Fe68Ni1
0Cr6B8C4 A general term for amorphous alloys, etc., and more preferably an alloy with an Fe content of 70% or more and a saturation magnetic flux density of 1.0T or more. For this reason, the saturation magnetic flux density of iron-based alloys is more than double that of Mn-Zn ferrite, which is around 0.5T, and in terms of noise impulse characteristics, the core volume can be smaller than that of conventional ferrite materials. For example, when the outer diameter is kept constant, the inner diameter can be made larger, that is, the wall thickness can be made thinner, and when the inner diameter is kept constant, the outer diameter can be made smaller. Consider taking advantage of this tolerance to improve the impedance characteristics at low frequencies.

The impedance characteristic is determined by the balance between inductive reactance and capacitive reactance, and as shown in FIG. 2, the noise attenuation characteristic peaks at a specific frequency fc. If you are trying to increase the inductance to increase the impedance in the low frequency range, the most effective way is to increase the number of windings by the square of the effective number. However, increasing the number of windings increases the influence of stray capacitance between the windings, which has the negative effect of shifting the peak fc to the lower frequency side. The problem here is fc
The question is whether or not it remains close to the practical range.

As a result of experiments with various windings, the inventors of the present invention found that even when the number of windings increases considerably, for example to about 50 turns, fc does not fall below 100 KHz. . In other words, increasing the number of core windings is the most effective way to improve the characteristics in the low frequency range of 100KHz to 500KHz, as required by VDE-0871, one of the West German ISM standards. There was found. In other words, the following calculation formula

[0009]

[Math 1]

where L: inductance μ: magnetic permeability t: thickness of toroidal core r2: outer radius of toroidal core r1: inner radius of toroidal core N: N as a function of r1 in the number of windings, that is, a certain area of the inner diameter If only η can be filled in

[0011]

[Math 2]

[0012] where d: winding diameter η: Filling rate becomes. Substituting this equation (2) into equation (1), we get

0013
]

[Math 3]

[0014] Here, the condition for ∂L/∂r1 = 0 to obtain the maximum inductance is r1 ~ 0.78r2
Figure 3 shows the relationship between L and (r1 /r2) that is satisfied by
Shown below. In other words, when the inner and outer diameters are around 0.78, the inductance becomes maximum. This core with an outside diameter ratio of around 0.78 is attached to a conventional core with an outside diameter ratio of around 0.6, and the inside diameters are compared as if they were the same. The invention method reduces the size by about 23%).

For example, when η=0.25, that is, when the inner diameter is 20 mm, the conventional method and the method of the present invention are considered to be equivalent, and the method of the present invention has an inner diameter of about 5 mm compared to the conventional method
3%, and when the inner diameter reaches 30mm, an inductance increase of about 113% can be expected. As described above, the present invention has made it possible to determine the optimal toroidal shape from the viewpoint of the noise attenuation characteristics and pulse attenuation characteristics of the iron-based alloy magnetic material, which has characteristics different from those of conventional ferrite materials.

[0016]

[Example] Hereinafter, an example in which the present invention is applied to a common mode choke material will be described. The core material is Fe73.5Si13, which is an iron-based amorphous alloy with a saturation magnetic flux density of 1.35T and an initial permeability of 5000 (at 1kHz).
．． An amorphous alloy (heat treatment temperature: 410 degrees x 1 hour) containing 3 atomic % of 5B9Pd1Nb was used. The material used has an outside diameter ratio of 0.75, an outside diameter of 40 mm, an inside diameter of 30 mm, and a thickness of 10 mm.
Using a core of mm, the number of turns of copper wire with a diameter of 1.4 mm is 5.1.
And so. On the other hand, the conventional comparison material had an inner/outer diameter ratio of 0.
5. The outer diameter is 40mm, the same as the actual material, and the inner diameter is 20mm.
A core with a thickness of 10 mm was used, and the number of turns of the copper wire with a diameter of 1.4 mm was 12. Figure 4 shows the measurement results of the noise attenuation characteristics by frequency. Compared to the comparison material, the example material exhibits superior noise attenuation characteristics in a wide frequency band.

[0017]

[Effects of the Invention] As detailed above, according to the present invention, from the inner and outer diameter ratio considering only the characteristics of the conventional ferrite core,
It became possible to design a core with an inner/outer diameter ratio that takes advantage of the characteristics of iron-based magnetic materials, and it was possible to manufacture a core with improved impedance characteristics. This new shape of the core is especially
Effective as a choke coil for MC.

[Brief explanation of drawings]

[Figure 1] Inner radius r1 and outer radius r2 of toroidal core
It is a figure showing thickness t.

FIG. 2 is a diagram showing a typical relationship between frequency and noise attenuation characteristics determined by the balance between inductive reactance and capacitive reactance.

FIG. 3 is a diagram showing the relationship between inner and outer diameter ratio and inductance.

FIG. 4 is a diagram showing an example of measurement of frequency and noise attenuation characteristics of a comparison material and an example material.

Claims (1)

[Claims] 1. An iron-based alloy toroidal core with excellent magnetic properties, characterized by an inner/outer diameter ratio of 0.78±0.1.