Electric lamp and discharge devices – With gas or vapor – Incandescent filament lamp
Reexamination Certificate
2001-04-02
2004-09-21
Husar, Stephen (Department: 2875)
Electric lamp and discharge devices
With gas or vapor
Incandescent filament lamp
C313S042000, C313S043000
Reexamination Certificate
active
06794818
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a fluorescent lamp that is operated with high frequencies in combination with an electronic ballast.
BACKGROUND ART
A large number of fluorescent lamps are turned on ordinarily with an electronic ballast, in which a capacitor is connected in parallel with a fluorescent lamp on the side opposed to a power source and in series with an electrode coil (hereinafter, this type of electronic ballast is referred to as a “C preheat type electronic ballast”). This is because a suitable electric current through a filament is required to preheat a fluorescent lamp cathode when it starts and to maintain the lighting, and a resonance voltage necessary for the lamp starting and operating should be ensured.
The reason this type of electronic ballast has spread most widely is that its circuit configuration is simple and inexpensive. In the C preheat type of electronic ballast, the current through a filament is relatively constant.
When a fluorescent lamp combined with the C preheat type of electronic ballast comes to the end of the life by the dissipation of the emissive coating on the electrode coil, the cathode fall voltage is raised. That results in the increase in the current through a filament, which causes the electrode coil to overheat by the excessive current. In addition to the heating from the electrode coil, an electrical discharge generates heat. Thus, the temperature in the vicinity of the electrode increases gradually. Under such circumstances, the lamp operation does not stop occasionally, even if the electrode coil is disconnected. In that case, the glass in the vicinity of the electrode between its terminals starts to be melted because of the constant-current property of the C preheat circuit, so that oscillation of the electronic ballast still continues after leakage of the fluorescent lamp.
In order to avoid these problems, the C preheat type of electronic ballast generally has the function of detecting a rise in the lamp voltage in accordance with a rise in the cathode fall voltage and cutting off an oscillation circuit beforehand or lowering an oscillation voltage to a safe level.
Furthermore, an electronic ballast in which another capacitor is added to the configuration of the above-described C preheat type of electronic ballast so as to be connected in parallel with a fluorescent lamp on the side nearer a power source (hereinafter, this type of electronic ballast is referred to as “double C type electronic ballast”) has been put to practical use before. This electronic ballast is doubted to be commercialized again in the future. For the double C type of electronic ballast, a large amount of oscillation voltage is always applied across the fluorescent lamp, even if the electrode coil is disconnected.
However, when the fluorescent lamp, which is combined with such a C preheat type of electronic ballast including a double C type for lighting, comes to the end of the life, the failure of detection of a rise in the lamp voltage, though it rarely occurs, may cause a bulb-end glass in the vicinity of the electrode, e.g., a stem glass to be melted, even if the electronic ballast has the function of detecting a rise in the lamp voltage and cutting off the oscillation circuit beforehand or lowering the oscillation voltage to a safe level. Thus, it has been demanded to solve these problems.
DISCLOSURE OF INVENTION
Therefore, with the foregoing in mind, it is an object of the present invention to provide a fluorescent lamp in which a bulb-end glass is not melted after an electrode coil is disconnected in the last period of electrode life when the fluorescent lamp is turned on with a C preheat type electronic ballast, including a double C type.
A fluorescent lamp of the present invention includes a bulb provided with a pair of electrode coils at both ends thereof. Each of the electrode coils is mounted between two lead wires held by a bulb-end glass. A means for preventing overheating of the bulb-end glass is mounted between the lead wires located between the electrode coil and the bulb-end glass. The means for preventing overheating connects the lead wires electrically just before or after the electrode coil is disconnected.
This configuration can provide a fluorescent lamp that offers the excellent advantage of keeping the bulb-end glass safely at lower temperatures by electrically connecting the lead wires with the means for preventing overheating and of preventing the bulb-end glass from being melted, when an emissive coating is dissipated in the last period of electrode life of the fluorescent lamp, which ordinarily would increase the temperature of the electrode and its vicinities extraordinarily.
In a fluorescent lamp of the present invention, the means for preventing overheating has a first preferred configuration including a glass member and a first and a second metallic pin for supporting the glass member. One end of each of the first and the second metallic pin is connected to the lead wires, respectively. The first and the second metallic pin are provided not in contact with each other.
According to this preferred configuration, the glass member is heated by a conductive heat, a radiant heat, and intermittent pulse discharge after the emissive coating on the electrode coil in the last period of the life is dissipated and before the electrode is disconnected. In particular, the glass member in the base of the metallic pin is heated effectively by the intermittent pulse discharge. When the electrode coil is disconnected, ionic conduction occurs in the glass member, and thus the glass member starts melting. Furthermore, the two metallic pins may come into contact with each other by the flow of the molten glass member. This contact stops the glass member from melting (i.e., ionic conduction is interrupted). However, the electrical conduction (electronic conduction) between the metallic pins is continued.
Referring to another phenomenon, an increase in the current through a filament after emissive coating dissipation may cause the glass member to start melting because of the heat radiated from the electrode coil, even before the electrode coil is disconnected. In such a case, metal atoms sputtered from the electrode coil enter the molten portion of the glass member and bridge the two metallic pins, so that electronic conduction between the two metallic pins is established. Thus, a transition from the ionic conduction by the melting of the glass member to the electronic conduction occurs between a pair of metallic pins, and thereby the electrical conduction can be continued.
During the above period, the bulb-end glass is not melted, so that the fluorescent lamp can be protected against an excessive heat and maintained safely. Furthermore, even if the lamp in the above condition is restarted after it is turned off, the bulb-end glass is not melted. Thus, the fluorescent lamp can be maintained safely.
According to the first preferred configuration, since the glass member is held by a pair of metallic pins at both ends thereof and each of the metallic pins is connected to the two lead wires, respectively, the glass member can be mounted easily between the lead wires.
In the first configuration, the means for preventing overheating further may include a metallic container in which the glass member is housed. At least one of the first and the second metallic pin supports the glass member indirectly by supporting the metallic container. The glass member is housed in the metallic container so that a portion of the glass member is exposed to a discharge space.
According to this configuration, when the electrode coil in the last period of the life, in which an emissive coating has been dissipated, is disconnected, the glass member starts melting and conducting ionically. However, since the glass member is housed in the metallic container, the molten state can be maintained in the metallic container without producing a significant deformation of the glass member. During this period, the bulb-end glass is not melted, so that the fluorescen
Kitagawa Kouichi
Myojo Minoru
Ueda Takashi
Husar Stephen
Macchiarolo Peter
Merchant & Gould P.C.
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