Electric power conversion systems – Current conversion – Cryogenic
Reexamination Certificate
2001-03-15
2003-07-15
Sheehan, John (Department: 1742)
Electric power conversion systems
Current conversion
Cryogenic
C363S148000, C148S304000
Reexamination Certificate
active
06594157
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to magnetic powder cores and to methods for making the same. In particular, the present invention relates to a low-coercive-force, low-loss magnetic powder core and a method for making the same. The present invention also relates to switching power supplies, various converter circuits, and active filters. Furthermore, the present invention relates to filters and amplifying devices, and particularly, relates to a low-loss filter outputting less distorted waveforms.
2. Description of the Related Art
As magnetic cores used in core components, such as transformer cores for switching power supplies and smoothing choke cores, which require a constant permeability up to the high frequency region, ferrite closed-magnetic-circuit cores, ferrite gapped cores, and amorphous-alloy-tape-wound cores provided with gaps have been proposed. Also, magnetic powder cores formed by compacting a mixture of a powder, such as carbonyl iron, permalloy, or sendust, and an insulating material have been proposed.
Ferrite sintered magnetic cores exhibit low core loss, but simultaneously exhibit small saturation magnetic flux densities. Thus, in ferrite closed-magnetic-circuit cores and ferrite gapped cores, a leakage magnetic flux from the gap section adversely affects peripheral electric circuits. Magnetic powder cores using powders of carbonyl iron, permalloy, and sendust have the disadvantage of large core loss, although the cores exhibit higher saturation magnetic flux densities compared to ferrite magnetic cores.
In recent years, development of electronic devices has advanced with an increase in the use thereof. In particular, the weight of the development was shifted toward reducing heat dissipation by reducing the size of the electronic devices and reducing the power loss. In order to achieve these aims, switching power supplies, various DC/DC converter circuits, and active filters have been improved. These devices use various types of magnetic elements having magnetic cores. Ferrite is mainly used for the magnetic cores. In some cases, carbonyl iron magnetic cores, FeAlSi-alloy magnetic powder cores, and FeNi-alloy magnetic powder cores are also used.
A ferrite magnetic core is generally provided with a gap to prevent magnetic saturation. A leakage magnetic flux from the gap will adversely affect peripheral circuits. On the other hand, a NiZn ferrite core exhibits a large core loss, resulting in high heat dissipation from a device using this core. A carbonyl magnetic powder core exhibits an extremely large core loss, resulting in significantly high heat dissipation compared to ferrite magnetic cores. In addition, in a FeAlSi-alloy magnetic powder core and a FeNi-alloy magnetic powder core, the core loss thereof is lower than that of the carbonyl iron magnetic powder core, but still does not reach required levels.
Low-pass filters have been used for smoothing the pulse shape output from impulse modulation amplifiers. The requirements for low-pass filters are low loss and less distortion of smoothed waveforms. A low-pass filter is generally provided with a capacitor and an inductor composed of a coil with a magnetic core. Achievement of these requirements strongly depends on properties of the magnetic core constituting the inductor. Thus, conventional low-pass filters use amorphous magnetic cores provided with gaps, ferrite cores provided with gaps, or carbonyl iron gap-free magnetic powder cores.
However, in filters using amorphous magnetic cores provided with gaps or ferrite cores provided with gaps, leakage magnetic fields from the gaps may adversely affect peripheral elements and circuits, resulting in decreased stability in the entire circuits including the filters and generation of noise. Moreover, in these filters, the amplitude permeability varies with changes in the magnetic field and exhibits a large rate of change. When a pulsed current causing a large change in magnetic field is smoothed, the waveform will be significantly distorted.
In the carbonyl iron gap-free magnetic powder cores, the dependence of the amplitude permeability on the magnetic field is constant, and the waveform is not distorted. However, the carbonyl iron gap-free magnetic powder cores dissipate a significant amount of heat due to large core loss.
The large core loss in conventional magnetic powder cores is due to large core loss of the magnetic materials themselves used for the magnetic powder and insufficient relaxation of stress which is applied during compacting of the magnetic powder cores.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a magnetic powder core having low coercive force and low core loss and a method for making the same.
It is another object of the present invention to provide a switching power supply, converter circuits, and active filters which exhibit low heat dissipation and which can be miniaturized.
It is another object of the present invention to provide a filter which dissipates less heat due to low loss and which suppresses waveform distortion, and an amplifying device provided with this filter.
According to a first aspect of the present invention, a magnetic powder core comprises a molded article of a mixture of a glassy alloy powder and an insulating material, the glassy alloy comprising Fe and at least one element selected from Al, P, C, Si, and B, having a texture primarily composed of an amorphous phase, and exhibiting a temperature difference &Dgr;T
x
, which is represented by the equation &Dgr;T
x
=T
x
−T
g
, of at least 20 K in a supercooled liquid, wherein T
x
indicates the crystallization temperature and T
g
indicates the glass transition temperature.
Since the magnetic powder core of the present invention comprises a mixture of the glassy alloy powder and the insulating material, the insulating material enhances the resistivity of the entire magnetic powder core. Thus, the magnetic powder core exhibits reduced core loss due to reduced eddy current loss and high permeability in a high-frequency region.
Preferably, the glassy alloy has a resistivity of at least 1.5 &mgr;&OHgr;•m. The eddy current loss in the glassy alloy particles in a high-frequency region is thereby effectively decreased, the magnetic powder core exhibiting further reduced core loss.
The magnetic powder has a coercive force of preferably 80 A/m or less and more preferably 40 A/m or less in an applied magnetic field of ±2.4 kA/m.
Preferably, the magnetic powder core has a core loss of 400 kW/m
3
or less under the conditions of a frequency of 100 kHz and a magnetic flux density of 0.1 T. This core loss is significantly smaller than that of known magnetic powder cores.
Preferably, the insulating material comprises a silicone rubber. The silicone rubber is effective for relieving the internal stress of the magnetic powder core.
Preferably, the glassy alloy is represented by the following formula:
(Fe
1-a
T
a
)
100-x-v-z-w
Al
x
(P
1-b
Si
b
)
v
C
z
B
w
wherein T represents at least one element of Co and Ni, and the subscripts a, b, x, v, z, and w satisfy the relationships, 0≦a≦0.15 by atomic ratio, 0<b≦0.8 by atomic ratio, 0 atomic percent<x≦20 atomic percent, 0 atomic percent<v≦22 atomic percent, 0 atomic percent<z≦12 atomic percent, and 0 atomic percent<w≦16 atomic percent.
The magnetic powder core of the present invention is formed of the above Fe-based glassy alloy powder in which the Fe content is higher than the Co and/or Ni content. Since this Fe-based glassy alloy exhibits higher saturation magnetic flux density than that of a Co-based glassy alloy, the magnetic powder core exhibits further improved magnetic characteristics.
According to a second aspect of the present invention, a method for making a magnetic powder core comprises a powder preparation step of preparing a powder of a glassy alloy comprising Fe and at least one element selected from Al, P, C, Si, and B, having a texture primarily composed of an amorphous p
Ikarashi Kazuaki
Kenmotsu Hidetaka
Mizushima Takao
Naito Yutaka
Yoshida Shoji
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Sheehan John
LandOfFree
Low-loss magnetic powder core, and switching power supply,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Low-loss magnetic powder core, and switching power supply,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Low-loss magnetic powder core, and switching power supply,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3043983