Electric lamp and discharge devices: systems – Current and/or voltage regulation – Automatic regulation
Reexamination Certificate
2000-02-14
2001-08-28
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
Automatic regulation
C315S307000, C315S362000
Reexamination Certificate
active
06281642
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ballast for a discharge lamp, and more particularly to an electronic ballast suitable for operating the discharge lamp utilized as a vehicular headlamp.
2. Description of the Prior Art
It is known that the discharge lamp will flicker repeatedly when coming near the end of the lamp life, resulting in an unreliable lamp operation as well as posing a stress to the ballast. In order to avoid this problem, U.S. Pat. No. 5,880,563 proposes to cease operating the lamp upon detecting the end of the lamp life. In this patent, the lamp flickering is monitored so as to determine the end of the lamp life when the number of the flickering out, i.e., unforced extinction of lamp exceeds a predetermined number. However, the scheme allows the lamp to flicker for some time period before ceasing the ballast, leaving an unstable lamp operation for some time period between the initial lamp extinction and the actual ceasing of the ballast. Thus, unreliable lamp operation still continues at the end of the lamp life, detracting from the safe lamp operation as well as still posing a stress to the ballast.
SUMMARY OF THE INVENTION
In view of the above problem, the present invention has been accomplished to provide a ballast for a discharge lamp which is capable of reliably and successfully detecting the end of the lamp life and ceasing the ballast immediately upon detection of the lamp's life end. The ballast of the present invention comprises a power supply providing from a power source a variable power to the discharge lamp, and a power controller which controls the power supply to apply a high voltage for igniting the lamp and subsequently apply a predetermined power for operating the lamp. A lamp life detector is included in the ballast to detect whether or not the lamp comes to a lamp's life end. Also included in the ballast is a supervisor which issues, upon detection of the lamp's life end, a disable signal prohibiting the power supply from lighting the discharge lamp. The characterizing feature of the ballast resides in that the power controller provides a detection period of a limited short time period starting from energization of the ballast such that the lamp life detector can detect the lamp's life end and issue a lamp's life end signal only when there is an extinction of lamp within the detection period, and that the supervisor issues, after the elapse of the detection period, an enable signal permitting the power supply to ignite the discharge lamp if the lamp is extinguished after the elapse of the detection period. The present invention is based upon the finding that the lamp coming its end of life will normally extinct within a short time after being ignited, while there is possibility of another lamp extinction which is not due to the lamp's life end but due to other reasons such as lowered input power or unstable arc discharge caused by physical shocks or vibrations as is seen when an automobile equipped with the lamp is running a bumpy road. Thus, according to the present invention, the lamp's life end can be reliably detected within the detection period of the limited short time, while the lamp can be successfully re-ignited if it is accidentally extinguished for the reason not due to the lamp's life end. The lamp's life end signal is issued from the lamp life detector when the power supply sees a lamp voltage above a predetermined level and/or sees a lamp current below a predetermined level.
The disable signal may be processed to cause the power supply to stop feeding the power to the discharge lamp for deenergization of the ballast. Alternatively, the disable signal may be processed to cause the power supply to shorten a period of applying the high voltage to the discharge lamp to such an extent as to fail to re-ignites the discharge lamp. Preferably, the detection period is set to range from 1 to 60 seconds, and most preferably from 1 to 10 seconds.
The power controller is preferred to provide an ignition period within which the power supply is permitted to apply the high voltage to the discharge lamp. The ignition period is set to start from the energization of the ballast and to be shorter than detection period, i.e., within the detection period. When there is acknowledged within the ignition period an event which would otherwise be detected as the lamp's life end, the lamp life detector issues no lamp life end signal, thereby avoiding a false detection of the lamp's life end at the time of igniting the lamp, and therefore assuring reliable lamp's life end detection.
Further, the ballast may be configured to include an input voltage monitor for monitoring an input voltage supplied to the power supply. Based upon the input voltage as well as operating conditions of the lamp, the power controller determines whether or not a forced lamp extinction comes from a drop in the input voltage. Thus, the power controller provides a forced lamp extinction signal indicative of that the lamp is caused to extinct due to the drop in the input voltage. Upon receiving the forced lamp extinction signal within the detection period, the supervisor acts to cancel the disable signal, thereby avoiding false deactivation of the ballast and assuring the reignition of the lamp.
These and still other objects and features of the present invention will become more apparent from the following description of the preferred embodiment when taken in conjunction with the attached drawings.
REFERENCES:
patent: 5880563 (1999-03-01), Toyama et al.
patent: 5973457 (1999-10-01), Yamashita et al.
patent: 6008592 (1999-12-01), Ribarich
patent: 6087776 (2000-07-01), Yamashita et al.
Kidera Kazunori
Konishi Hirofumi
Nakamura Toshiaki
Lee Wilson
Matsushita Electric & Works Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wong Don
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