Ferrite and ferrite core for power supply

Details Ferrite and ferrite core for power supply Ferrite and ferrite core for power supply

1995-12-27

1998-12-08

Bonner, Melissa

Compositions

Magnetic

Iron-oxygen compound containing

252 6254, 252 6262, 252 6263, H01F 134, C01G 4900, C04B 3538

Patent

active

058464484

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a manganese-zinc system ferrite for use as cores of electric power supplies, typically power supply transformers operating at a high frequency of about 10 to 500 kHz and a core for power supply constructed by the ferrite.


BACKGROUND ART

Manganese-zinc system ferrite is often used to form cores for use in coils and transformers of various communication equipment and commercial appliances. Since the recent trend is to use power supplies of higher frequency, core materials of performance meeting such purposes are now required. In particular, switching power supplies need transformers which operate at a power of several tens of watts and a high frequency band of 10 to 500 kHz. Also required are cores for transformers intended for motor drive, signal amplification and oscillation purposes. Transformer cores are conventionally formed of low-loss ferrites of manganese-zinc system. However, since the power loss also known as core loss is substantial in a high frequency region of 10 to 500 kHz, there is a demand for an improvement in core loss. Various proposals have been made in this respect.
Such proposals included addition of oxides of Si and Ca and further addition of oxides of tetravalent metals such as Sn, Ti and Zr as well as oxides of pentavalent metals such as V, Nb and Ta. Examples of the sole or combined addition of oxides of tetra- or pentavalent metals are found in Japanese Patent Application Kokai (JP-A) Nos. 2880/1971, 72696/1973, 262404/1985, 108109/1986, 252609/1986, 252611/1986, 222018/1988, 129403/1989, 54902/1990, 141611/1991, 163804/1991, 223119/1991, 248403/1991, 248404/1991, 248405/1991, 254103/1991, 55362/1992, 150007/1992, 198416/1993, 267040/1993, etc.
These proposals, however, fail to increase the difference between maximum magnetic flux density Bm and residual magnetic flux density Br, .DELTA.B=Bm-Br, at a high frequency of e.g., 100 kHz and 100.degree. C., to reduce the power loss at the high frequency, and to increase effective magnetic permeability (.mu.a) associated with a .mu.a-B curve. As a consequence, when transformers are formed of these conventional ferrites, it is difficult to reduce the size of transformers.


DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a ferrite having a low power loss as well as large .DELTA.B=Bm-Br at high frequency and an improved .mu.a-B curve and a core for a power supply using the same.
This and other objects are achieved by the present invention which is defined below as (1) to (11).
(1) A ferrite characterized by comprising oxide, and zirconium oxide as subordinate components, wherein calculated as MnO and the content of zinc oxide is 6 to 16 mol % calculated as ZnO, and components is such that to 3,000 ppm calculated as TiO.sub.2, and the total of tin oxide and titanium oxide is at least 300 ppm, O.sub.5, and
(2) The ferrite of (1) wherein the content of niobium oxide based on the main components is at least 50 ppm calculated as Nb.sub.2 O.sub.5 and the content of zirconium oxide based on the main components is at least 50 ppm calculated as ZrO.sub.2.
(3) The ferrite of (1) or (2) wherein the content of niobium oxide based on the main components is 100 to 400 ppm calculated as Nb.sub.2 O.sub.5.
(4) The ferrite of any one of (1) to (3) wherein the weight ratio of P based on the main components is 0 to 30 ppm.
(5) The ferrite of any one of (1) to (4) wherein the weight ratio of B based on the main components is 0 to 50 ppm.
(6) The ferrite of any one of (1) to (5) which has a power loss of up to 300 kW/m.sup.3 at a temperature of 100.degree. C. when an AC magnetic field of 100 kHz and 200 mT is applied.
(7) The ferrite of (6) which has an eddy current loss of up to 200 kW/m.sup.3 at a temperature of 100.degree. C. when an AC magnetic field of 100 kHz and 200 mT is applied.
(8) The ferrite of any one of (1) to (7) wherein when an AC magnetic field of 100 kHz is applied at a temperature of 100.degree. C., the resulting hysteresis curve has a .DELTA.B value of at least 220 mT

REFERENCES:
patent: 5143638 (1992-09-01), Yamazaki et al.
Database WPI, Derwent Publications, AN-93-371315, JP-A-05-267040, Oct. 15, 1993.
Database WPI, Derwent Publications, AN-91-371847, JP-A-03-248403, Nov. 6, 1991.

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