The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Sep. 15, 1998
Filed:
May. 10, 1996
Sreeraman Venkitasubrahmanian, Torrance, CA (US);
Clint Mason, Buena Park, CA (US);
Yongping Xia, Torrance, CA (US);
Feng-Kang Hu, Palos Verdes Estates, CA (US);
Jaap Schlejen, Shanghai, CN;
Philips Electronics North America, New York, NY (US);
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.