Electric lamp and discharge devices: systems – Current and/or voltage regulation – Automatic regulation
Reexamination Certificate
1996-06-25
2001-09-18
Shingleton, Michael B. (Department: 2817)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
Automatic regulation
C315S2090SC, C315S224000, C315S082000, C315SDIG007, C315SDIG002
Reexamination Certificate
active
06291945
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a lighting device or a starting device for a high-voltage discharge lamp such as a metal halide lamp. Here, the lighting device or the starting device is of the type using an alternating current (AC) or a rectangular-wave current.
2. Description of the Prior Art
It is known to light or start a high-voltage discharge lamp such as a metal halide lamp by using an alternating current (AC). In the case where such a discharge lamp in a cold state is started, the intensity of light generated by the discharge lamp remains low until the pressure of a metal vapor therein rises to a sufficient level.
Japanese published unexamined patent application 5-144577 corresponding to U.S. Pat. No. 5,365,152 discloses a discharge-lamp lighting apparatus including a lighting control circuit. During a time of starting the discharge lamp, the lighting control circuit serves to control its output in response to a length of the last off-time and an on-time after the start of discharging. In the discharge-lamp lighting apparatus of Japanese application 5-144577, a power supplied to the discharge lamp is controlled in response to the output of the lighting control circuit.
Some of the prior-art AC-based lighting devices for high-voltage discharge lamps have a problem as follows. Immediately after a high-voltage discharge lamp in a cold state is started by using AC power, the discharge lamp tends to go out upon a change of the polarity or direction of a lamp current between a positive side and a negative side.
SUMMARY OF THE INVENTION
It is a first object of this invention to provide a discharge-lamp lighting device which prevents a discharge lamp, being low in electrode temperature, from going out immediately after the discharge lamp is started.
It is a second object of this invention to provide a discharge-lamp lighting device having two advantageous functions as follows. The first advantageous function is to prevent a discharge lamp, being low in electrode temperature, from going out immediately after the discharge lamp is started. The second advantageous function is to prevent one of the discharge-lamp electrodes from diminishing in size even in the case where every starting of the discharge lamp uses a direct-current (DC) power or a low-frequency power.
A first aspect of this invention provides a lighting device for a discharge lamp which comprises a power supplying circuit for supplying electric power to the discharge lamp; a current detecting circuit for detecting a lamp current which flows through the discharge lamp; and a control circuit for enabling the power supplying circuit to supply one of a direct-current electric power and a low-frequency electric power to the discharge lamp during a time interval in starting the discharge lamp, for adjusting a duration time of supply of a one-polarity electric power to the discharge lamp in accordance with a magnitude of the lamp current detected by the current detecting circuit, and for enabling the power supplying circuit to supply an alternating-current electric power to the discharge lamp after the time interval elapses.
A second aspect of this invention is based on the first aspect thereof, and provides a lighting device wherein the control circuit is operative for adjusting the duration time of supply of the one-polarity electric power to the discharge lamp in accordance with a value of integration of the lamp current.
A third aspect of this invention is based on the second aspect thereof, and provides a lighting device wherein the control circuit is operative for, in cases where the low-frequency electric power is supplied to the discharge lamp, adjusting a ratio between portions of the time interval which correspond to a positive-current flow time and a negative-current flow time respectively so that the value of integration of the lamp current in a positive side and the value of integration of the lamp current in a negative side are approximately equal to each other.
A fourth aspect of this invention is based on the second aspect thereof, and provides a lighting device wherein the control circuit includes a capacitor, and a current controlling circuit for charging and discharging the capacitor with currents depending on the lamp current.
A fifth aspect of this invention is based on the second aspect thereof, and provides a lighting device wherein the control circuit includes a capacitor, a current controlling circuit for charging and discharging the capacitor with charging and discharging currents depending on the lamp current during the time interval, and a current increasing circuit for increasing the charging and discharging currents after the time interval elapses.
A sixth aspect of this invention is based on the first aspect thereof, and provides a lighting device wherein the control circuit includes a lamp current increasing circuit for increasing the lamp current during a predetermined time in the start of the discharge lamp.
A seventh aspect of this invention provides a lighting device for a discharge lamp which comprises a starting switch movable into an on position; first means for sensing a lamp current which flows through the discharge lamp; second means connected to the starting switch for alternately feeding a positive-direction current and a negative-direction current to the discharge lamp after the starting switch moves into the on position; and third means connected to the first means and the third means for controlling a time length of continuous feed of each of the positive-direction current and the negative-direction current to the discharge lamp by the second means in response to the lamp current sensed by the first means.
An eighth aspect of this invention is based on the seventh aspect thereof, and provides a lighting device further comprising fourth means connected to the second means for enabling a time length of a first cycle of alternate feed of the positive-direction current and the negative-direction current to be longer than a time length of each of a second cycle and later cycles of alternate feed of the positive-direction current and the negative-direction current.
A ninth aspect of this invention provides a lighting device for a discharge lamp which comprises a starting switch movable into an on position; first means connected to the starting switch for feeding an alternating current of a variable frequency to the discharge lamp after the starting switch moves into the on position; and second means connected to the first means for increasing the frequency of the alternating current in accordance with lapse of time.
A tenth aspect of this invention is based on the ninth aspect thereof, and provides a lighting device further comprising third means for sensing a lamp current which flows through the discharge lamp, and fourth means connected to the first means and the third means for controlling the frequency of the alternating current in response to the lamp current sensed by the third means.
REFERENCES:
patent: 5319286 (1994-06-01), Leyten
patent: 5365152 (1994-11-01), Ozawa et al.
patent: 5486740 (1996-01-01), Yamashita et al.
patent: 5-144577 (1993-06-01), None
Aida Kenji
Kato Koichi
Toyama Koichi
Nippondenso Co. Ltd.
Pillsbury & Winthrop LLP
Shingleton Michael B.
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