Inductor devices – With permanent magnet
Reexamination Certificate
2001-11-29
2004-06-22
Nguyen, Tuyen T. (Department: 2832)
Inductor devices
With permanent magnet
C336S233000, C335S302000
Reexamination Certificate
active
06753751
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic core (hereafter, may be briefly referred to as “core”) of an inductor component, for example, choke coils and transformers. In particular, the present invention relates to a magnetic core including a permanent magnet for magnetic bias.
2. Description of the Related Art
Regarding conventional choke coils and transformers used for, for example, switching power supplies, usually, the alternating current is applied by superimposing on the direct current. Therefore, the magnetic cores used for these choke coils and transformers have been required to have an excellent magnetic permeability characteristic, that is, magnetic saturation with this direct current superimposition does not occur (this characteristic is referred to as “direct current superimposition characteristic”).
As high-frequency magnetic cores, ferrite magnetic cores and dust cores have been used. However, the ferrite magnetic core has a high initial permeability and a small saturation magnetic flux density, and the dust core has a low initial permeability and a high saturation magnetic flux density. These characteristics are derived from material properties. Therefore, in many cases, the dust cores have been used in a toroidal shape. On the other hand, regarding the ferrite magnetic cores, the magnetic saturation with direct current superimposition has been avoided, for example, by forming a magnetic gap in a central leg of an E type core.
However, since miniaturization of electronic components has been required accompanying recent request for miniaturization of electronic equipment, magnetic gaps of the magnetic cores must become small, and requirements for magnetic cores having a high magnetic permeability for the direct current superimposition have become intensified.
In general, in order to meet this requirement, magnetic cores having a high saturation magnetization must be chosen, that is, the magnetic cores not causing magnetic saturation in high magnetic fields must be chosen. However, since the saturation magnetization is inevitably determined from a composition of a material, the saturation magnetization cannot be increased infinitely.
A conventionally suggested method for overcoming the aforementioned problem was to cancel the direct current magnetic field due to the direct current superimposition by incorporating a permanent magnet in a magnetic gap formed in a magnetic path of a magnetic core, that is, to apply the magnetic bias to the magnetic core.
This magnetic bias method using the permanent magnet was superior method for improving the direct current superimposition characteristic. However, since when a metal-sintered magnet was used, an increase of core loss of the magnetic core was remarkable, and when a ferrite magnet was used, the superimposition characteristic did not be stabilized, this method could not be put in practical use.
As a method for overcoming the aforementioned problems, for example, Japanese Unexamined Patent Application Publication No. 50-133453 discloses that a rare-earth magnet powder having a high coercive force and a binder were mixed and compression molded to produce a bonded magnet, the resulting bonded magnet was used as a permanent magnet for magnetic bias and, therefore, the direct current superimposition characteristic and an increase in the core temperature were improved.
However, in recent years, requirements for the improvement of power conversion efficiency of the power supply have become even more intensified, and regarding the magnetic cores for choke coils and transformers, superiority or inferiority cannot be determined based on only the measurement of the core temperature. Therefore, evaluation of measurement results using a core loss measurement apparatus is indispensable. As a matter of fact, the inventors of the present invention conducted the research with the result that even when the resistivity was a value indicated in Japanese Unexamined Patent Application Publication No. 50-133453, degradation of the core loss characteristic occurred.
Furthermore, since miniaturization of inductor components has been even more required accompanying recent miniaturization of electronic equipment, requirements for low-profile magnet for magnetic bias have also become intensified.
In recent years, surface-mounting type coils have been required. The coil is subjected to a reflow soldering treatment in order to surface-mount. Therefore, the magnetic core of the coil is required to have characteristics not being degraded under this reflow conditions. In addition, a rare-earth magnet having oxidation resistance is indispensable.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a magnetic core including a permanent magnet as a magnet for magnetic bias arranged in the neighborhood of a gap in order to supply magnetic bias from both sides of the gap to the magnetic core including at least one gap in a magnetic path with ease at low cost, while, in consideration of the aforementioned circumstances, the aforementioned magnetic core has superior direct current superimposition characteristic, core loss characteristic, and oxidation resistance, and the characteristics are not degraded under reflow conditions.
It is another object of the present invention to provide a magnet especially suitable for miniaturizing the magnetic core including the permanent magnet as a magnet for magnetic bias arranged in the neighborhood of a gap in order to supply magnetic bias from both sides of the gap to the magnetic core including at least one gap in a magnetic path of a miniaturized inductor component.
According to an aspect of the present invention, there is provided a permanent magnet having a resistivity of 0.1 &OHgr;·cm or more. The permanent magnet is a bonded magnet containing a magnet powder dispersed in a resin, and the magnet powder is composed of a powder coated with inorganic glass, and the powder has an intrinsic coercive force of 5 KOe or more, a Curie point Tc of 300° C. or more, and a particle diameter of the powder of 150 &mgr;m or less. According to another aspect of the present invention, there is provided a magnetic core which includes a permanent magnet as a magnet for magnetic bias arranged in the neighborhood of a magnetic gap in order to supply magnetic bias from both sides of the gap to the magnetic core including at least one magnetic gap in a magnetic path. Furthermore, another magnetic core including a permanent magnet having a total thickness of 10,000 &mgr;m or less and a magnetic gap having a gap length of about 50 to 10,000 &mgr;m is provided.
According to still another aspect of the present invention, there is provided an inductor component includes a magnetic core including at least one magnetic gap having a gap length of about 50 to 10,000 &mgr;m in a magnetic path, a magnet for magnetic bias arranged in the neighborhood of the magnetic gap in order to supply magnetic bias from both sides of the magnetic gap, and a coil having at least one turn applied to the magnetic core. The magnet for magnetic bias is a bonded magnet containing a resin and a magnet powder dispersed in the resin and having a resistivity of 1 &OHgr;·cm or more. The magnet powder is a rare-earth magnet powder having an intrinsic coercive force of 5 KOe or more, a Curie point of 300° C. or more, a maximum particle diameter of 150 &mgr;m or less, and an average particle diameter of 2.5 to 50 &mgr;m and coated with inorganic glass. The rare-earth magnet powder is selected from the group consisting of a Sm—Co magnet powder, Nd—Fe—B magnet powder, and Sm—Fe—N magnet powder. Furthermore, another inductor component including a magnetic core and a bonded magnet is provided. The magnetic core includes a magnetic gap having a gap length of about 500 &mgr;m or less, and the bonded magnet has a resistivity of 0.1 &OHgr;·cm or more and a thickness of 500 &mgr;m or less.
According to yet another aspect of the present invention, there is provided an inductor component to be su
Ambo Tamiko
Fujiwara Teruhiko
Hoshi Haruki
Ishii Masayoshi
Isogai Keita
Frishauf Holtz Goodman & Chick P.C.
NEC Tokin Corporation
Nguyen Tuyen T.
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