JPH07257967A - Ni-containing low loss ferrite for power source - Google Patents

Abstract

PURPOSE:To reduce the core loss and increase the resistivity by specifying the P content of a sintered compact contg. Fe2O3, NiO and ZnO. CONSTITUTION:A mixture of 40-52.5mol% Fe2O3 having <=10ppm P content with 5-47.5mol% NiO, <=35mol% ZnO and CuO is temporarily burnt and crushed to obtain burnt powder. This powder is blended with a binder, granulated, compacted into a ring-shaped core and burnt to obtain the objective Ni-contg. low loss ferrite for a power source having <=66ppm P content.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferrite material used for transformers such as switching power supplies and liquid crystal backlights.

[0002]

2. Description of the Related Art Switching power supplies and liquid crystal backlights have been widely used in consumer equipment, office automation equipment, and industrial equipment, and are currently being made smaller, thinner, and lighter. Conventionally, a Mn-based ferrite core has been used for the transformer used for the switching power supply, the liquid crystal backlight, and the like.

[0003]

The Mn-based ferrite core has a large saturation magnetic flux density and permeability, and a loss (core loss) of about 10 kW / m ³ (50 kHz, 50 mT).
It has been used for transformers such as switching power supplies and liquid crystal backlights. However, the resistivity is relatively low, about 10 Ω · m, and leakage current occurs when the core is directly wound. For this reason,
When a Mn-based ferrite core is used as a transformer for a switching power supply or the like, the core is covered with a bobbin or treated with an insulating film or the like before winding.
There is a problem that the manufacturing cost is high and miniaturization is difficult. On the other hand, the Ni-based ferrite core has a very high resistivity of about 10 ⁶ Ω · m and can be wound directly on the core, but the loss (core loss) is 60 kW / m.
^Since it is as large as about ³ (50 kHz, 50 mT), the core easily generates heat and is not suitable for a transformer such as a switching power supply. In view of the above, an object of the present invention is to provide a ferrite material having a high resistivity and a small loss (core loss), which can be used as a transformer for a switching power supply or the like.

[0004]

According to the present invention, in order to solve the above problems, Fe ₂ O ₃ 40 to 52.5 mol.
%, NiO 5-47.5 mol%, ZnO 35m
In a ferrite material whose main component is a composition of ol% or less, the content of P in the sintered body is less than 66 ppm. In the present invention, the reason why the composition range of the ferrite material is limited is as follows. When Fe ₂ O ₃ exceeds 52.5 mol% or NiO is less than 5 mol% among the main components, the resistivity is low and the core cannot be directly wound. When ZnO exceeds 35 mol%, the Curie temperature becomes 100 ° C. or lower, which is not practical. Further, when the P content in the sintered body is 66 ppm or more, the loss (core loss) increases. Therefore, the main component composition shown in the claims is limited. If the ferrite material of the present invention has the above composition,
The manufacturing method is not particularly limited.

[0005]

With the conventional Ni-based ferrite material, as described above, the loss (core loss) is 60 kW / m ³ (50 kHz,
It was as large as 50 mT) and was not suitable for a transformer such as a switching power supply. In the present invention, as a result of researching a Ni-based ferrite material that can be used as a transformer for a switching power source, etc., when the content of P contained in the sintered body is large, P segregates in the crystal structure of the sintered body. It was found that the loss (core loss) increases when the segregation of P occurs. That is, when the content of P in the sintered body is less than 66 ppm, there is no segregation of P and the loss (core loss) is 30 k.
It is less than W / m ³ (50 kHz, 50 mT) and can be used as a transformer for switching power supplies.

[0006]

EXAMPLES Examples of the ferrite material according to the present invention will be described in detail below. F with a P content of 10 ppm or less
e ₂ 0 ₃ 49.45 mol%, ZnO 29.75mo
1%, NiO 14.80 mol% and CuO 6.
A raw material powder in an amount equivalent to 00 mol% was weighed, and a predetermined amount of ion-exchanged water was added to the raw material powder.
Mix for an hour and use an electric furnace at a maximum temperature of 850 ° C for 1.5
After calcination for a period of time, this is cooled in a furnace and crushed with a 40 mesh sieve. After that, a material to which a predetermined amount of ion-exchanged water has been added is pulverized by a ball mill for 6 hours, and the pulverized slurry raw material is dried and pulverized. A binder (polyvinyl alcohol) was added to this and granulated, and the granules sized with a 40-mesh sieve were used with a dry compression molding machine and a mold to have an outer diameter of 16.8 mm, an inner diameter of 8.5 mm, and a height of 5 Molding pressure of 1.5 ton / cm on a 4 mm ring-shaped core
Molded in ² and fired in air at 1100 ° C. for 1.5 hours. After measuring the firing density of each of the obtained samples, 2 under the conditions of a frequency of 50 kHz and a magnetic flux density of 50 mT.
The loss (core loss) was measured in the temperature range of 0 to 140 ° C. The results are shown in Fig. 1. Further, the crystal structure (crystal grain size, composition distribution) of the sintered body was observed. According to this example, to the extent that it can be sufficiently used as a power ferrite,
A Ni-based ferrite with a small core loss could be obtained. Further, there was no segregation of P in the crystal structure. Further, using the same raw materials other than the main component composition and Fe ₂ O ₃ and the same sample preparation method, samples were prepared using various Fe ₂ O ₃ having different P contents, The firing density and the loss (core loss) were measured under the same conditions as above, and the crystal structure (crystal grain size, composition distribution) of the sintered body was observed. The results are shown in Table 1.

[0007]

[Table 1]

As can be seen from Table 1, P in the sintered body
When the content of P was less than 66 ppm, there was no segregation of P in the crystal structure, and a low-loss (core loss of 30 kW / m ³ or less) ferrite was obtained. Moreover, the firing density is 5.1 × 10.
^{When it was} less than ³ kg / m ³ or when the crystal grain size was 10 μm or more, the loss (core loss) was large. Moreover, when the content of P in the sintered body exceeded 66 ppm, segregation of P or the like was observed in the crystal structure of the sintered body, the composition distribution became non-uniform, and the loss (core loss) increased. The content of P contained in the sintered body, Fe ₂ 0 ₃ content in the raw material and the Fe ₂
It was calculated from the content of P in the 0 ₃ raw material. For Example 3 in Table 1, when the content of P in the sintered body was analyzed by ICP (Dielectric Coupling Plasma Atomic Emission Spectroscopy), the measured value was 45 ppm, which was almost the same as the value obtained by the above calculation method. Matched Next, Fe ₂ O ₃ 49.60 mol% with a P content of 10 ppm or less, ZnO 32.80mo
1% and NiO 17.60 mol% equivalent raw material powders were weighed, a ring-shaped core was formed by the same procedure as in the above-mentioned example, and this was fired at 1200 ° C. for 1.5 hours in the atmosphere. The firing density and the loss (core loss) of each of the obtained samples were measured under the same conditions as in the above-mentioned examples. Further, the crystal structure (crystal grain size, composition distribution) of the sintered body was observed. Furthermore, the raw materials other than the main component composition and Fe ₂ O ₃ are the same,
Also, using the same procedure as the sample preparation method, samples were prepared using various Fe ₂ O ₃ having different P contents, and the firing density and loss (core loss) were measured under the same conditions as in the above-mentioned examples, and sintering was performed. The crystal structure of the body (crystal grain size, composition distribution) was observed. The results are shown in Table 2.

[0009]

[Table 2]

As can be seen from Table 2, P in the sintered body
When the content of is less than 66 ppm, the loss (core loss) is 30 kW / m ³ or less, which is a significant improvement. When the firing density was less than 5.1 × 10 ³ kg / m ³ or when the crystal grain size was 10 μm or more, the loss (core loss) was slightly increased as in Example 1. Further, when the content of P in the sintered body exceeded 66 ppm, segregation of P was observed in the crystal structure of the sintered body, and the loss (core loss) increased. From the above results, it is clear that by suppressing the P content in the sintered body to less than 66 ppm, the loss (core loss) is significantly improved and a low loss ferrite material can be obtained. Further, it is desirable that the firing density is 5.1 × 10 ³ kg / m ³ or more, or the crystal grain size is less than 10 μm.
Other Ni-based ferrites (Ni-Mg-Cu-Zn
With respect to ferrite and Ni—Mg—Zn ferrite), the same examination as above was performed, and by suppressing the P content in the sintered body to less than 66 ppm, the loss (core loss) was significantly improved.

[0011]

INDUSTRIAL APPLICABILITY In the Ni ferrite material, by suppressing the content of P in the sintered body to less than 66 ppm, a ferrite material with a small loss (core loss) and a high resistivity can be obtained, which is used for transformers such as switching power supplies It is possible to reduce the manufacturing cost and size of the transformer.

[Brief description of drawings]

FIG. 1 is a diagram showing temperature characteristics of loss (core loss) of a Ni-based low loss magnetic material according to the present invention.

Claims (1)

[Claims] 1. Fe ₂ O ₃ 40-52.5 mol%, N
A low-loss ferrite for a Ni-based power source, characterized in that the main component is a composition of 5 to 47.5 mol% of iO and 35 mol% or less of ZnO, and the content of P in the sintered body is less than 66 ppm.