Electric lamp and discharge devices: systems – Pulsating or a.c. supply – Induction-type discharge device load
Reexamination Certificate
2001-03-02
2003-11-18
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
Induction-type discharge device load
C315S344000, C315S348000, C313S484000, C252S062620
Reexamination Certificate
active
06650068
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a core for an induction coil, an illumination unit using the same, and a polycrystalline ferrite. More particularly, the present invention relates to a core for an induction coil used for a discharge lamp that generates an electromagnetic field inside a bulb, which contains discharge gas therein, by means of the induction coil.
FIG. 7
schematically illustrates a cross-sectional construction of an illumination unit that generates plasma discharge by means of an induction coil. The illustrated illumination unit includes: a translucent bulb
101
containing discharge gas such as inert gas and metal vapor inside; and an induction coil
102
placed in a cavity
108
formed in the center of the bulb
101
. The induction coil
102
is essentially composed of a core (magnetic material)
102
a
and a winding
102
b
wound around the core
102
a.
The induction coil
102
is electrically connected to a high-frequency power supply circuit
103
for supplying high-frequency power via a matching circuit
104
. The matching circuit
104
is provided to match the impedance between the induction coil
102
and the high-frequency power supply circuit
103
for efficient transfer of high-frequency power to the bulb
101
. The high-frequency power supply circuit
103
and the matching circuit
104
are housed in a circuit case
105
.
When a high-frequency current in the range of several megahertz to several hundred megahertz is applied to the induction coil
102
from the high-frequency power supply circuit
103
, ring-shaped plasma discharge
106
is generated inside the bulb
101
. Generation of the plasma discharge
106
causes emission of ultraviolet light or visible light, whereby light output is obtained. In practice, the oscillating frequency of the high-frequency power supply circuit
103
is 13.56 MHz or several megahertz in the ISM band.
An example of the core
102
a
suitably usable for the illumination unit described above is disclosed in Japanese Laid-Open Patent Publication No. 7-99042. The publication describes a core having a loss of 150 mW/cm
3
or less when measured at room temperature with a frequency of 3 MHz and a magnetic flux density of 10 mT, and discloses that Ni—Zn ferrite material is suitable as the material satisfying this condition.
When Ni—Zn ferrite material is used for the core
102
a,
it is preferable to set the operating frequency of the high-frequency power supply circuit
103
at a high frequency of several megahertz (or in the range of several megahertz to several tens of megahertz) from the standpoint of the physical properties of the Ni—Zn ferrite material. In order to realize such high-frequency operation, however, a large-size noise filter is required to suppress line noise generated from the high-frequency power supply circuit
103
. This disadvantageously increases the volume of the high-frequency power supply circuit
103
. In other words, the illumination unit using the core
102
a
made of a Ni—Zn ferrite material has a problem that a large-size noise filter is additionally required and thus downsizing of the illumination unit is difficult.
Moreover, in the case where high-frequency noise is radiated or propagated from the unit, extremely strict regulations are imposed for prevention of the noise. In order to satisfy these regulations, therefore, an expensive noise filter must be used for the illumination unit. This poses a big barrier against attempt of cost reduction of the illumination unit.
SUMMARY OF THE INVENTION
An object of the present invention is providing an induction coil core operable in a comparatively low frequency range (50 kMz to 1 MHz inclusive) and an illumination unit using such a core.
Another object of the present invention is providing a polycrystalline ferrite usable as the material of the above induction coil core.
The induction coil core of the present invention is a core used for an induction coil of a discharge lamp, the discharge lamp including: a bulb containing discharge gas inside; and the induction coil for generating an electromagnetic field with a frequency in a range of 50 kHz to 1 MHz inclusive in the bulb, wherein the core is made of a Mn—Zn polycrystalline ferrite and has a Curie temperature of 270° C. or more.
In one embodiment, the Curie temperature is 290° C. or more.
In another embodiment, the Mn—Zn polycrystalline ferrite includes Fe, Mn, and Zn where Fe element occupies 72 wt. % or more of all elements excluding oxygen.
In still another embodiment, the Mn—Zn polycrystalline ferrite includes Fe, Mn, and Zn and also includes Ni as an additive.
In still another embodiment, the core has a characteristic of being able to receive a magnetomotive force of 600 ampere-turn or more under the conditions of room temperature, a frequency of 100 kHz in the electromagnetic field, and a cross-sectional area of a face of the core vertical to a direction of magnetic flux of 120 mm
2
.
The illumination unit of the present invention includes: a bulb containing discharge gas inside; an induction coil for generating an electromagnetic field with a frequency in a range of 50 kHz to 1 MHz in the bulb; and a power supply for supplying power to the induction coil, wherein the induction coil includes a core and a winding, and the core is made of a Mn—Zn polycrystalline ferrite and has a Curie temperature of 270° C. or more.
In one embodiment, the Curie temperature is 290° C. or more.
In another embodiment, the induction coil has a characteristic of being able to receive a magnetomotive force of 600 ampere-turn or more under the conditions of room temperature, a frequency of 100 kHz in the electromagnetic field, and a cross-sectional area of a face of the coil vertical to a direction of magnetic flux of 120 mm
2
.
In still another embodiment, the induction coil is placed in a cavity in the center of the bulb formed by deforming a portion of an outer wall of the bulb into a concave shape, a phosphor is applied to an inner wall of the bulb, and the discharge gas includes at least rare gas.
In still another embodiment, the illumination unit is a self-ballasted fluorescent lamp.
The polycrystalline ferrite of the present invention includes Fe, Mn, and Zn where Fe element occupies 72 wt. % or more of all elements excluding oxygen, the ferrite having a Curie temperature of 270° C. or more.
Alternatively, the polycrystalline ferrite of the present invention includes Fe, Mn, and Zn and also including Ni as an additive, the ferrite having a Curie temperature of 270° C. or more.
In one embodiment, Fe element occupies 60 wt. % or more of all elements excluding oxygen.
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patent: 2551711 (1951-05-01), Snoek et al.
patent: 4473542 (1984-09-01), David
patent: 5626789 (1997-05-01), Varshney
patent: 6057649 (2000-05-01), Van Der Zaag et al.
patent: 2002/0067129 (2002-06-01), Chamberlain et al.
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patent: 1 344 132 (1974-01-01), None
patent: 1 583 260 (1981-01-01), None
patent: 06-349622 (1994-12-01), None
patent: 7-99042 (1995-04-01), None
patent: 07-099042 (1995-04-01), None
patent: 2000-182816 (2000-06-01), None
patent: 2000-348683 (2000-12-01), None
patent: 130551 (1990-03-01), None
European Search Report, Dated Aug. 16, 2001.
Notice of Reasons for Rejection, Japanese Patent Office, Mailing Date Dec. 3, 2002.
Kurachi Toshiaki
Miyazaki Koji
Seki Katsushi
Takeda Mamoru
Cole Thomas W.
Matsushita Electric - Industrial Co., Ltd.
Nixon & Peabody LLP
Vu David
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