JP2007115969A - METHOD OF DESIGNING FERRITE CORE AND MnZn FERRITE CORE FOR NOISE FILTER - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of designing a ferrite core and an MnZn ferrite core for a noise filter to attain the noise filter having a high frequency and a high impedance. <P>SOLUTION: In the method of designing a ferrite core for a noise filter formed of an MnZn ferrite and the MnZn ferrite core, a relation between the cross-sectional area Ae of the ferrite core and the resistivity ρ of the material of the core satisfies a defined requirement of Ae/ρ<10 mm<SP>2</SP>×(Ω cm)<SP>-1</SP>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for designing a ferrite core for noise filter and a MnZn ferrite core.

  In recent years, technological innovations due to downsizing and higher performance of electronic devices have been remarkably advanced. Accordingly, there is a demand for higher performance of the MnZn-based ferrite used, for example, higher magnetic permeability and lower loss. In particular, a ferrite core for a noise filter is required to have a high initial permeability and impedance.

  In particular, with regard to noise filters, in recent years, as shown in the standard (CISPR Pub. 22 B.), wideband noise removal from a low frequency region is required. In order to remove noise in the low frequency region, it is necessary to increase the impedance in the low frequency region. Characteristics satisfying the following two conditions are required for the material constituting the noise filter. The first condition is to increase the magnetic permeability of the material, and the second condition is to maintain a high magnetic permeability frequency characteristic up to a higher frequency region.

The first condition for improving the high magnetic permeability is to control the magnetocrystalline anisotropy constant K ₁ and the magnetostriction constant λ of MnZn ferrite. Specifically, the main component composition is controlled to a composition in the vicinity of 51 to 53 mol% Fe ₂ O ₃ , 22 to 28 mol% MnO, and the balance ZnO. In this composition region, the magnetocrystalline anisotropy constant K ₁ of MnZn ferrite becomes small, and high permeability can be achieved. The high magnetic permeability MnZn ferrite currently on the market is manufactured in this range. In order to increase the magnetic permeability, there is a method of adding an additive such as Bi ₂ O ₃ , MnO ₃ , V ₂ O ₅ or the like that enlarges the crystal grain size in order to make the crystal structure largely uniform.

An improvement method for maintaining the frequency characteristic of the high permeability of the second condition up to a higher frequency region is to increase the specific resistance of the material constituting the noise filter. Specifically, an element capable of forming a grain boundary layer such as SiO ₂ or CaO is added. By forming a sufficient grain boundary layer, the eddy current flowing back through the MnZn ferrite core can be suppressed, so that the eddy current loss that is dominant in the high frequency region can be reduced. As a result, the loss in the high frequency region can be reduced, so that the frequency characteristic of high permeability can be maintained up to the higher frequency region.

Further, it is known that there is a remarkable effect in a core having a cross-sectional area of 100 mm ² or more by controlling the distribution of physical properties such as the specific resistance value and the lattice constant Fe ²⁺ content of the spinel phase within a predetermined range. 1 is disclosed.

JP 2002-134331 A

  It is extremely difficult to realize a material constituting a noise filter that satisfies the above two conditions at the same time. If the crystal grains are enlarged in order to satisfy the first condition described above, a sufficient specific resistance cannot be obtained, resulting in an increase in eddy current and a decrease in magnetic permeability in a high frequency region. It was. Further, when an additive capable of forming a grain boundary layer is added, there is a problem that a high magnetic permeability cannot be realized because a sufficiently large crystal grain cannot be obtained.

Further, since the above-mentioned Patent Document 1 is a method for improving the core loss by controlling the distribution of physical properties such as the specific resistance value, the lattice constant of the spinel phase, and the Fe ²⁺ content within a predetermined range, the specific resistance value There is a problem in that the core loss characteristics greatly depend on the distribution state, material composition distribution, and Fe ²⁺ content.

  The present invention has been made to solve the above-described problems, and a technical problem thereof is to provide a noise filter ferrite core and a method for designing a MnZn ferrite core that realize a high-frequency, high-impedance noise filter. .

The first invention for achieving the above object is a ferrite core for a noise filter composed of a MnZn ferrite core, wherein the relationship between the cross-sectional area Ae of the core and the specific resistance of the material constituting the ferrite core is ρ, This is a ferrite core for noise filter that satisfies the condition defined by Ae / ρ <10 mm ² × (Ω · cm) ⁻¹ .

According to a second invention for achieving the above object, in the method for designing an MnZn ferrite core, the relationship between the cross-sectional area Ae of the core and the specific resistance of the material constituting the ferrite core is represented by Ae / ρ <10 mm ^2. This is a method for designing a MnZn ferrite core that satisfies the condition defined by × (Ω · cm) ⁻¹ .

According to the present invention, in the design method of the ferrite core for noise filter and the MnZn ferrite core composed of the MnZn ferrite core, the relationship between the cross-sectional area Ae of the core and the specific resistance of the material constituting the ferrite core is represented by Ae. By satisfying the condition defined by / ρ <10 mm ² × (Ω · cm) ⁻¹ , the dominant eddy current loss can be reduced in the high frequency region. As a result, it is possible to provide a design method for a ferrite core for noise filter and a MnZn ferrite core that realizes a high-frequency, high-impedance noise filter.

  A method for designing a ferrite core for noise filter and a MnZn ferrite core according to the best mode for carrying out the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing the frequency characteristics of magnetic permeability of a ferrite core for noise filter of the present invention (invention product 3 in Table 1).

In the design method of the ferrite core for noise filter and the MnZn ferrite core according to the best mode for carrying out the present invention, 51.5 mol% of Fe ₂ O ₃ , 24.0 mol% of ZnO, the main component of the remaining MnO and SiO _The subcomponents of 0 to 0.05 wt%, ₂ to 0.05 wt% of CaO, and 0.01 to 0.1 wt% of Bi ₂ O ₃ are weighed. Then, it mixes for 2 hours using an attritor. After mixing, granulate with a spray dryer. Thereafter, the mixed powder is pre-fired in an atmosphere of 850 ° C. for 2 hours. Thereafter, the pre-baked powder obtained is pulverized with an attritor. After pulverization, the mixture is granulated with a spray dryer to produce a toroidal sample having a core cross-sectional area Ae of 5 to 50 mm ² and fired at a firing temperature of 1350 ° C.

  Thereafter, the specific resistances of the present invention and the comparative example, the magnetic permeability of 1 kHz, the Ae / ρ value, and the critical frequency fr are evaluated by changing the specific resistance of the material constituting the ferrite core, which is a toroidal sample. Table 1 shows the measurement results of the specific resistance of the present invention and the comparative example, the magnetic permeability of 1 kHz, the Ae / ρ value, and the critical frequency fr in which the specific resistance of the material constituting the ferrite core is changed. Note that a frequency that is 5% lower than the permeability μ ′ (μ′1 kHz) of 1 kHz is defined as the critical frequency fr.

From Table 1, it can be seen that the example of the present invention that satisfies the condition defined by Ae / ρ <10 mm ² × (Ω · cm) ⁻¹ exhibits a high value of fr of 8 to 150 Hz.

The MnZn ferrite core, which is a ferrite core for noise filters, has a core cross-sectional area Ae satisfying the condition defined by Ae / ρ <10 mm ² × (Ω · cm) ⁻¹ in the cross-sectional area Ae and the specific resistance ρ. By designing the MnZn ferrite core, the dominant eddy current loss can be reduced in the high frequency region, so that the frequency characteristics of high permeability can be maintained up to the higher frequency region.

In general, the eddy current loss is proportional to the square of the frequency f, the square of the eddy current radius d, and the inverse of the material specific resistance ρ. In the material composition of the MnZn ferrite core of the present invention, since the specific resistance is as low as 10 ⁻¹ to 10 ¹ Ω · cm, eddy current flows in the cross section of the MnZn ferrite core. That is, the eddy current radius d can be reduced by reducing the cross section of the MnZn ferrite core. Since the eddy current radius d can be reduced, eddy current loss can be reduced, and the frequency characteristics of high permeability can be maintained up to a higher frequency region. As a result, it is possible to provide a design method for a ferrite core for noise filter and a MnZn ferrite core that realizes a high-frequency, high-impedance noise filter.

The figure which shows the frequency characteristic of the magnetic permeability of the ferrite core for noise filters of this invention.

Claims (2)

In a ferrite core for a noise filter composed of an MnZn ferrite core, the relationship between the cross-sectional area Ae of the core and the specific resistance of the material constituting the ferrite core is ρ: Ae / ρ <10 mm ² × (Ω · cm) ^{− A} ferrite core for a noise filter characterized by satisfying the conditions defined in ¹ . In the MnZn ferrite core design method, the relationship between the cross-sectional area Ae of the core and the specific resistance of the material constituting the ferrite core ρ is defined as Ae / ρ <10 mm ² × (Ω · cm) ⁻¹ The design method of the MnZn ferrite core characterized by satisfying the above.

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