JPH07257966A - Ni-containing low loss ferrite for power source - Google Patents

Abstract

PURPOSE:To obtain a ferrite material ensuring a small loss (core loss) and usable as a material of the transformer of a switching power source, etc., with an Ni-contg. ferrite having high resistivity. CONSTITUTION:This Ni-contg. low loss ferrite is a sintered compact based on a compsn. consisting of 40-52.5mol% Fe2O3, 5-47.5mol% NiO and <=35mol% ZnO and having <66ppm P content, >=5.1X10<3>kg/m<3> sintered density and <=10mum grain size.

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]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides Fe ₂ O _{3 of} 40 to 52.5 mol%,
NiO 5-47.5 mol%, ZnO 35 mol%
A ferrite containing the following composition as a main component,
The content of P in the sintered body is less than 66 ppm, the firing density is 5.1 × 10 ³ kg / m ³ or more, and the grain size is 10 μm.
m or less. In the present invention, the reason why the composition range of the ferrite material is limited is as follows.
When Fe2O3 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. ZnO is 3
When it exceeds 5 mol%, the Curie temperature becomes 100 ° C. or lower, which is not practical. Therefore, the main component composition shown in the claims is limited. Moreover, the firing density is 5.1 × 10 ³ kg.
If it is less than / m ³ or the crystal grain size exceeds 10 μm, the loss (core loss) increases. The ferrite material of the present invention is not particularly limited in its production method as long as it has the above composition.

[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 supply or the like, when the content of P is large, P is segregated in the crystal structure of the sintered body, and this P segregation occurs. It has been found that the loss (core loss) increases when the occurrence of the above occurs, and when the content of P in the sintered body is less than 66 ppm, the segregation of P in the crystal structure of the sintered body is suppressed and the loss becomes low. When the firing density is 5.1 × 10 ³ kg / m ³ or more and the crystal grain size is 10 μm or less, the loss (core loss) is 30 kW.
/ M ³ or less (50 kHz, 50 mT), a low loss, and a ferrite material that can be used as a transformer for a switching power supply or the like can be obtained.

[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 O 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, a predetermined amount of ion-exchanged water was added thereto, and the mixture was mixed in a ball mill for 4 hours and calcined at a maximum temperature of 850 ° C. for 1.5 hours using an electric furnace. Then, this is cooled in an oven 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,
It was possible to obtain a Ni-based ferrite with a small loss (core loss). 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 using the same sample preparation method, samples were prepared using various Fe ₂ O ₃ with different P contents. The firing density and 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
Content of less than 66 ppm, firing density of 5.1 × 10 ³
In the case of kg / m ³ or more and the crystal grain size is 10 μm or less,
There is no segregation of P in the crystal structure and low loss (core loss is 30
Ferrite of kW / m ³ or less) was obtained. In addition, the content of P contained in the sintered body is the amount of Fe ₂ O ₃ in the raw material and the content of F.
It was calculated from the content of P in the e ₂ O 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, P content of 10 ppm or less Fe ₂ O ₃ 49.60 mol%, 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 those 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
Content of less than 66 ppm, firing density of 5.1 × 10 ³
In the case of kg / m ³ or more and the crystal grain size is 10 μm or less,
There is no segregation of P in the crystal structure and low loss (core loss is 30
Ferrite of kW / m ³ or less) was obtained. In addition, the same examination as above was performed for other Ni-based ferrites (Ni-Mg-Cu-Zn ferrite, Ni-Mg-Zn ferrite), and it was found that the P content in the sintered body was 66p.
The loss (core loss) was significantly improved by suppressing the calcination density to less than pm, the firing density to 5.1 × 10 ³ kg / m ³ or more, and the crystal grain size to 10 μm or less.

[0011]

EFFECT OF THE INVENTION In the Ni-based ferrite material, the content of P in the sintered body is less than 66 ppm and the firing density is 5.1 ×.
By controlling the crystal grain size to 10 ³ kg / m ³ or more and the crystal grain size to 10 μm or less, a ferrite material having a small loss (core loss) and a high resistivity can be obtained, which is useful for a transformer such as a switching power supply. The manufacturing cost can be reduced and the size can be reduced.

[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
The main component is a composition of 5 to 47.5 mol% of iO and 35 mol% or less of ZnO, the content of P in the sintered body is less than 66 ppm, and the firing density is 5.1 × 10 ^3.
A low-loss ferrite for Ni-based power supplies, which has a crystal grain size of 10 μm or less at kg / m ³ or more.