Electric lamp and discharge devices: systems – Pulsating or a.c. supply – Induction-type discharge device load
Reexamination Certificate
2002-08-27
2003-11-04
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
Induction-type discharge device load
C313S046000
Reexamination Certificate
active
06642671
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrodeless discharge lamp.
2. Description of the Related Art
In recent years, from the standpoint of protection of a terrestrial environment, resource saving has been advocated in various industries. An effective measure to save the resources for a lamp is to obtain a longer operating lifetime. An electrodeless discharge lamp has been receiving considerable attention because its operating lifetime is typically several times longer than that of a discharge lamp having an electrode with a filament.
The structure of an electrodeless discharge lamp is different from that of a conventional fluorescent lamp having a filament. For example, an electrodeless discharge lamp includes: an electrodeless bulb filled with a light emitting material; an induction coil for providing electromagnetic energy that excites the light emitting material (discharge gas) in the bulb so as to allow the material to emit light; and a high frequency power supply circuit for supplying high frequency electric power to the induction coil.
The core of the induction coil of the electrodeless discharge lamp includes a magnetic material. If the temperature of the magnetic core of the induction coil increases during a discharging operation of the lamp and exceeds a certain critical temperature (Curie temperature), the magnetic permeability of the magnetic core decreases so that the operation of the discharge lamp is stopped. Thus, the electrodeless discharge lamp should have a structure that decreases the temperature of the induction coil.
The electrodeless discharge lamp has a long operating lifetime, but the lifetime is not unlimited, because the lifetime of electric components used in the lamp is finite. The lifetime of the electric components depends on the temperature. Especially, the lifetime of an electrolytic capacitor used in the power supply circuit of the electrodeless discharge lamp largely varies according to its environmental temperature. As the environmental temperature increases by 10° C., the lifetime of the electrolytic capacitor is decreased by half, which is known as the “Arrhenius' 10-degree rule”. Thus, the electrodeless discharge lamp should have a structure that decreases the temperature of the electric components.
Under such circumstances, considerable effort has been made to decrease the temperatures of the induction coil and the electric components incorporated in the electrodeless discharge lamp as much as possible.
For example, Japanese Utility Model Publication for Opposition No. 6-6448 discloses a known technique for decreasing the temperature of a magnetic core of an induction coil. According to this technique, a stick-shaped heat conducting member is incorporated in a central portion of a cross-section of the magnetic core along a longitudinal direction of the magnetic core for releasing heat generated in the induction coil. The stick-shaped heat conducting member is connected to a metal jacket, which is a casing of the induction coil, such that the heat conducted through the stick-shaped heat conducting member is radiated from the casing. The metal jacket extends from the lamp so as to radiate the heat.
In the above structure disclosed in Japanese Utility Model Publication for Opposition No. 6-6448, the heat generated in the magnetic core of the induction coil is transmitted to the metal jacket, which is a casing of the induction coil. This technique can decrease the temperature of the induction coil, but on the other hand, the temperature of the electric components included in the power supply circuit provided inside the casing is increased due to the heat transmitted to the casing.
Japanese Utility Model Publication for Opposition No. 6-6448 does not discuss issues concerning heat liberation from the electric components.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, an electrodeless discharge lamp includes a bulb filled with discharge gas; an induction coil for generating an electromagnetic field in the bulb; a power supply circuit which includes a plurality of electric components and which supplies electric power to the induction coil; a case for accommodating the plurality of electric components, the case having a surface which faces an external element of the electrodeless discharge lamp; a stick-shaped heat conducting member placed along a winding axis of the induction coil; a first planar heat conducting member placed so as to be perpendicular to the winding axis, the first heat conducting member being thermally connected to the stick-shaped heat conducting member; a second heat conducting member thermally connected to the first heat conducting member; and a third heat conducting member for thermally connecting at least two of the plurality of electric components, wherein the second heat conducting member is thermally connected to the case, and the thermal conductivity of the first heat conducting member is lower than the thermal conductivity of the stick-shaped heat conducting member and the thermal conductivity of the second heat conducting member.
In one embodiment of the present invention, the first heat conducting member is made of an electrically insulative material.
In another embodiment of the present invention, the first heat conducting member is made of a ferrite material.
In still another embodiment of the present invention, the thermal conductivity of the first heat conducting member is between about 0.8 W/m·K and about 6 W/m·K inclusive; and the thermal conductivity of the stick-shaped heat conducting member and the second heat conducting member is between about 100 W/m·K and about 400 W/m·K inclusive.
According to another aspect of the present invention, an electrodeless discharge lamp includes: a bulb filled with discharge gas; an induction coil for generating an electromagnetic field in the bulb; a power supply circuit which includes a plurality of electric components and which supplies electric power to the induction coil; a case for accommodating the plurality of electric components, the case having a surface which faces an external element of the electrodeless discharge lamp; a stick-shaped heat conducting member placed along a winding axis of the induction coil; a second heat conducting member thermally connected to the stick-shaped heat conducting member at a joint surface; and a third heat conducting member for thermally connecting at least two of the plurality of electric components, wherein the second heat conducting member is thermally connected to the case, and a product of the thermal conductivity of the stick-shaped heat conducting member and the area of a cross-section of the stick-shaped heat conducting member which is perpendicular to a central axis of the stick-shaped heat conducting member is smaller than a product of the thermal conductivity of the second heat conducting member and the area of the joint surface.
In one embodiment of the present invention, the electrodeless discharge lamp further includes a reduction member placed between the induction coil and the second heat conducting member for reducing a thermal influence caused by an electromagnetic field generated by the induction coil on the second heat conducting member.
In another embodiment of the present invention, the reduction member is made of a ferrite material.
According to still another aspect of the present invention, an electrodeless discharge lamp includes: a bulb filled with discharge gas; an induction coil for generating an electromagnetic field in the bulb; a power supply circuit which includes a plurality of electric components and which supplies electric power to the induction coil; a case for accommodating the plurality of electric components, the case having a surface which faces an external element of the electrodeless discharge lamp; a stick-shaped heat conducting member placed along a winding axis of the induction coil; a first planar heat conducting member placed so as to be perpendicular to the winding axis, the first heat conducting m
Kominami Satoshi
Kurachi Toshiaki
Miyazaki Kouji
Sasaki Ken-ichi
Takahashi Kenichirou
Matsushita Electric - Industrial Co., Ltd.
Snell & Wilmer LLP
Tran Thuy Vinh
Wong Don
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