Electric lamp and discharge devices – With envelope – Having base and connector
Reexamination Certificate
1999-07-01
2001-10-02
Patel, Nimeshkumard D. (Department: 2879)
Electric lamp and discharge devices
With envelope
Having base and connector
C313S318010, C313S317000, C362S021000, C362S294000
Reexamination Certificate
active
06297585
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fluorescent lamp that includes an end cap formed of synthetic resin, a manufacturing method for such a fluorescent lamp, and to a lighting apparatus that uses the same.
2. Prior Art
A known problem for fluorescent lamps is that the temperature of the electrode seals at the ends of a fluorescent tube rises sharply as the fluorescent tube approaches the end of its operating life.
The improvements in efficiency of fluorescent lamps and the concurrent reductions in their size and weight have led to an increase in the use of fluorescent lamp apparatuses. Such apparatuses use high-frequency inverter lighting circuits to light the fluorescent tubes. However, a particular problem has been observed when a fluorescent tube used in such an apparatus reaches the end of its operating life. When the emissive material that is originally present within the electrode filament has been dispersed, the cathode drop voltage increases and so prevents the fluorescent lamp from illuminating. However, the high-frequency inverter lighting circuit will continue to supply a preheating voltage to the electrode filament, so that electrode filament will remain in its preheated state. As a result, arc discharge occurs between the lead wires inside the electrode which increases the temperature of the electrode seal.
It is believed that the above problem is caused by the high current-feed capacity of the high-frequency inverter lighting circuit.
The above problem is especially prevalent in compact single-ended fluorescent lamps where the fluorescent tubes have a relative small diameter and two electrode seals are enclosed within a single end cap formed of synthetic resin. In conventional compact single-ended fluorescent lamps, the electrode seals that act as the problematic heat sources are located alongside one another, so that the aforementioned rise in temperature is especially marked. Heat dissipation is also poor, since the synthetic resin end cap encloses the two electrode seals. These factors result in an excessive rise in temperature which in extreme cases can lead to deformity in the end cap.
Japanese Laid-Open Patent Application H02-192650 discloses a technology that can prevent such rises in temperature at the ends of a fluorescent lamp. A thermal fuse is provided near the end of the fluorescent tube, so that when the temperature at the end of the fluorescent tube rises at the end of the operating life of the fluorescent tube, the thermal fuse will melt, thereby breaking the lighting circuit.
This technology has the thermal fuse located on the outside of the fluorescent lamp. This results in the thermal fuse being visible, which spoils the external appearance of such lamps. When a fluorescent lamp is formed by connecting four or more fluorescent tubes to a single end cap, it would be possible to keep the thermal fuses hidden from view by placing them in a space on the back side of the end cap. However, no such space is conventionally available on an end cap, so that it has only been possible to provide the thermal fuses on the outside of the cap where they will be clearly visible.
SUMMARY OF THE INVENTION
In view of the stated problems, it is a first object of the present invention to provide a fluorescent lamp that has a rationalized construction whereby the positioning of thermal protection elements on the outside of the fluorescent lamp can be avoided.
It is a second object of the present invention to provide a fluorescent lamp with a novel construction whereby thermal protection elements are enclosed within the end cap.
It is a third object of the present invention to provide a fluorescent lamp with a novel construction whereby thermal protection elements are kept from being visible with an end cap that has the same outer dimensions as conventional models;
It is a fourth object of the present invention to provide a fluorescent lamp with a construction where a thermal protection element is thermally coupled to each end of a fluorescent tube.
It is a fifth object of the present invention to provide a single-ended fluorescent lamp that includes thermal protection elements and has a rationalized construction;
It is a sixth object of the present invention to provide a manufacturing method for a fluorescent lamp with a rationalized construction whereby the positioning of thermal protection elements on the outside of the fluorescent lamp can be avoided.
It is a seventh object of the present invention to provide a manufacturing method that can attach thermal protection elements to a fluorescent lamp that has an end cap made of synthetic resin.
It is an eighth object of the present invention to a lighting apparatus that has a plurality of fluorescent lamps with thermal protection elements connected in series and is suited to high-frequency illumination
The above first object can be realized by a fluorescent lamp, including: a fluorescent tube that has an electrode sealed at each end by an electrode seal; a thermal protection element that is sensitive to ambient temperature and is capable of disconnecting an internal circuit; an end cap that has a first cavity and a second cavity formed in one surface and an electrode terminal that protrudes from another surface, the first cavity being adjacent to the second cavity, where one end of the fluorescent tube is inserted into the first cavity so that the electrode seal at the inserted end is enclosed by the end cap, and the thermal protection element is embedded into the second cavity so as to be thermally coupled to the electrode seal at the inserted end of the fluorescent tube, with one terminal of the thermal protection element being connected to a lead wire of the fluorescent tube and another terminal being connected to an electrode terminal.
With the stated construction, a thermal protection element is located close to the electrode seal to which it is thermally coupled. The thermal protection element is therefore sensitive to the rise in temperature that occurs in the electrode seal at the end of the operating life of the fluorescent lamp, and so quickly breaks the circuit.
Here, if through-holes are provided in the side wall between the first cavity and the second cavity, an improved thermal coupling can be achieved between the electrode seals of the fluorescent tube and the thermal protection elements. As an additional benefit, the final assembly process that fills the remaining spaces in the first and second cavities with synthetic material can be achieved by injecting the material at only one position, which simplifies the assembly of the fluorescent lamp.
Since the remaining spaces in the first and second cavities are filled with synthetic material, the thermal protection elements and the electrode seals are firmly attached to the end cap. The openings in the second cavities are also covered with lids, giving the fluorescent lamp a pleasing external appearance.
The above first object can be realized by a fluorescent lamp, including: a fluorescent tube that is formed with both tube ends being adjacent and has an electrode seal which seals a thermonic cathode-type electrode at each tube end; a pair of thermal protection elements that are sensitive to ambient temperature and are capable of disconnecting an internal circuit; a single end cap that has a pair of first cavities and a pair of second cavities in one main surface and electrode terminals that protrude from another main surface, each first cavity being adjacent to a different one of the second cavities, where each end of the fluorescent tube is inserted into each first cavity so that the end cap encloses the electrode seals, and the thermal protection elements are embedded into the second cavities so as to be thermally coupled to the electrode seals, and each thermal protection element has one terminal connected to a lead wire of the fluorescent tube and another terminal connected to one of the electrode terminals.
Here, in the above fluorescent lamp, each of the pair. of the second cavities may be formed i
Itaya Kenji
Tashiro Yoji
Matushita Electric Industrial Co. Ltd.
Patel Nimeshkumard D.
Price and Gess
Santiago Mariceli
LandOfFree
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