Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Periodic switch cut-out
Patent
1996-05-10
1998-09-15
Pascal, Robert J.
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Periodic switch cut-out
315127, 315224, H05B 3702
Patent
active
058084223
ABSTRACT:
A ballast for a gas discharge lamp includes a detection circuit which detects an operating state of the lamp in which the lamp current for the column discharge of one polarity is different from the lamp current for the column discharge of the other polarity by detecting the DC component of the voltage across the discharge lamp. The detection circuit includes (i) a device coupled such that a DC voltage is imposed there across when the lamp current is different for the column discharge according to one polarity verses the other polarity, and (ii) a sensing circuit for sensing the DC voltage across the device. The device may be a capacitive device, and in a particularly inexpensive implementation, is a DC blocking capacitor or a ballast capacitor. The sense circuit senses when the DC voltage across the device exceeds a threshold value, which may corresponds to fully-rectified state of the lamp or more favorably, to a lesser state of imbalance. In another embodiment, the variance in the DC voltage across the lamp is detected at the midpoint of a bridge inverter. A control circuit changes the output of the ballasting circuit when the DC voltage exceeds the threshold value to turn off the lamp or to recurrently cycle the lamp on and off to signal the user that the lamp needs to be changed.
REFERENCES:
patent: 5187414 (1993-02-01), Fellows et al.
patent: 5475284 (1995-12-01), Lester et al.
patent: 5574335 (1996-11-01), Sun
Hu Feng-Kang
Mason Clint
Schlejen Jaap
Venkitasubrahmanian Sreeraman
Xia Yongping
Pascal Robert J.
Philips Electronics North America
Vu David H.
Wieghaus Brian J.
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