Inductor devices – Core
Reexamination Certificate
1999-12-27
2002-05-21
Donovan, Lincoln (Department: 2832)
Inductor devices
Core
C336S083000, C336S096000, C336S200000
Reexamination Certificate
active
06392525
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magnetic element such as an conductor, a choke coil, a transformer, or the like in electronic equipment, particularly a miniature magnetic element used under a large current and to a method of manufacturing the same.
BACKGROUND OF THE INVENTION
With the reduction in size and thickness of electronic equipment, the reduction in size and thickness of components and devices used therein also has been demanded strongly. On the other hand, LSIs such as a CPU and the like have come to be made up of an increasing number of circuit components and a current of several amperes to several tens of amperes may be supplied to a power circuit provided in the LSIs. Therefore, similarly an inductor such as a choke coil used therein has been required to reduce its size, to lower the resistance, although being contrary to the size reduction, by enlarging the cross-sectional area of a coil conductor, and not to lower the inductance greatly with DC bias. The operation frequency has come to be higher and therefore it has been required that the loss in a high frequency area is low. Furthermore, in order to reduce the cost, it has been necessary that component elements with simple shapes can be assembled in easy processes. In other words, it has been demanded that a miniaturized thin inductor that can be used under a large current and at a high frequency is provided at a low cost.
In the case where an inductor is formed by providing a winding around a toroidal core, the inductance of the inductor is expressed by the following formula:
L~&mgr;×S=N
2
/r
wherein L indicates inductance, &mgr; magnetic permeability, S the cross-sectional area of a magnetic path, N the number of turns, and r the length of the magnetic path. From this formula, it is understood that a large value of L is obtained when the magnetic permeability &mgr;, the cross-sectional area S of a magnetic path, and the number of turns N are increased and the length r of the magnetic path is reduced. However, when the magnetic permeability is increased, the magnetic flux density is saturated even at a small current value. The magnetic permeability is decreased at higher current values, thus deteriorating the DC bias characteristics (the inductance value (L) characteristics dependent on a direct current). The enlargement of the cross-sectional area of the magnetic path is contrary to the size reduction and results in a long lead wire in the case of the same number of turns, thus causing a high resistance. The use of a lead wire with a large cross-sectional area to prevent this further goes against the size reduction. The increase in number of turns is contrary to the size reduction and also causes a high resistance. To shorten the magnetic path leads to the size reduction but the number of turns cannot be increased in that case. Therefore, generally it has been difficult to obtain a miniature inductor that has a high inductance, excellent DC bias characteristics, and a low resistance in a winding and that can be used not only at low frequencies but also at high frequencies.
An inductor that has been used practically will be described as follows.
In an EE-type or EI-type ferrite core and a coil that have been used most commonly, because a ferrite material has a relatively high magnetic permeability and a lower saturation magnetic flux density compared to that of a metallic magnetic material, the inductance is decreased greatly due to the magnetic saturation when the ferrite material is used without being modified, resulting in poor DC bias characteristics. Therefore, in order to improve the DC bias characteristics, usually such a ferrite core and a coil have been used by providing a gap in any position in a magnetic path of the core to decrease the apparent magnetic permeability.
In an inductor in which a Fe—Si—Al based alloy, a Fe—Ni based alloy, or the like that has a higher saturation magnetic flux density than that of ferrite is used as a core material, because such a metallic material has a low electrical resistance, the increase in high operation frequency to several hundreds of kHz to MHz as in the recent situation results in the increase in eddy current loss and thus the inductor cannot be used without being modified. Therefore, a so-called dust core has been used, which is obtained by superposing members, which have been formed to have thin bodies, via an insulating layer or which is formed using a pulverized material that is insulated.
It also has been proposed to combine and use a plurality of magnetic bodies. One obtained by winding a coil around a ferrite core with rib and then dipping them into a mixed solution of magnetic powder and a resin material (JP-A-61-136213) and one obtained by preparing two members formed through the superposition of a plurality of thin magnetic metal bodies, providing a planar coil between the two members, and fixing magnetic powder with a dispersed adhesive (JP-A-9-270334) have been described as being effective for reducing the size of an inductor. In addition, one obtained by providing a planar coil between two ferrite sheets and fixing ferrite powder with a dispersed adhesive in order to reduce the leakage flux has been proposed (JP-A-6-342725), although it is not described as achieving the size reduction.
With respect to the configurations of inductors, many conventional inductors have been formed of an EE or EI type core and a coil. However, in order to obtain a thin inductor, JP-A-9-92540 describes using one formed by winding the coil spirally in a plane. Further, JP-A-9-205023 describes that the terminal on the internal circumference side (hereinafter referred to as an “inner terminal”) of a spirally wound coil is lead out by providing a cutout in a core, so that the thickness corresponding to that of the lead wire is reduced.
However, when a ferrite material is used and a gap is provided anywhere in a magnetic path to decrease the apparent magnetic permeability, there has been a problem that a core vibrates in this gap portion when being operated with an alternating current, thus generating noise.
When thin metallic magnetic bodies with a high saturation magnetic flux density are superposed via insulating layers, the thin bodies that can be used at high frequencies should be formed to be sufficiently thin. Therefore, the cost increases and no complicated shape can be formed, which have been problems. Further, in order to obtain a dust core with characteristics good enough, it is necessary to make the dust core dense by the application of a very high pressure of about 10t/cm
2
in a molding process. Therefore, there have been problems that a special high-strength mold is required and complicated shapes are formed with difficulty.
In the types disclosed in JP-A-61-136213 and JP-A-6-342725 that are included in the types in which a plurality of magnetic bodies are combined and used, a member obtained by dispersing ferrite in a resin is used. However, since there is a limitation in the filling rate of the ferrite, there has been a problem that the saturation magnetic flux density of this member is low and therefore the DC bias characteristics are poor. Furthermore, in the type disclosed in JP-A-9-270334, the kind of the magnetic body to be mixed with resin is not described, but it is necessary to prepare a member formed by superposing a plurality of thin magnetic metal bodies in all cases, resulting in a high cost. In addition, since the upper and lower surfaces of an element are formed of metallic magnetic bodies, the electrical resistance is low and therefore insulation is required, and complicated shapes cannot be formed, which also have been problems.
SUMMARY OF THE INVENTION
The present invention seeks to provide a magnetic element, such as an inductor, a choke coil, a transformer, or the like, that is suitable for the use under a large current in various types of electronic equipment.
A magnetic element of the present invention includes: a composite magnetic member A containing a metallic magnetic powder in an amount of 50
Asahi Toshiyuki
Hirano Koichi
Inoue Osamu
Kato Jun-ichi
Nakatani Seiichi
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P,C,
Nguyen Tuyen T.
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