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:
Jul. 17, 2012
Filed:
Oct. 26, 2009
Naoki Komatsu, Kobe, JP;
Naoki Komatsu, Kobe, JP;
Panasonic Corporation, Osaka, JP;
Abstract
An electronic ballast is provided for adjustable filament preheating of a discharge lamp based on output current symmetry. A power converter receives DC power and outputs AC power. A starting circuit generates a high voltage for starting the lamp. A control circuit controls the AC power output from the power converting circuit. A symmetry determining circuit determines a positive-negative symmetrical state of the AC power output to the lamp with respect to ground. After lamp startup, the control circuit enters a filament heating operation in which the output frequency of the power converting circuit is controlled to a first frequency. At one or more predetermined current detection points during the filament heating operation, the control circuit checks the symmetry state. If the output current is symmetrical at the current detection point, the control circuit ends the frequency heating operation and enters steady state operation with an output frequency of the power converter controlled to a second frequency for maintaining lamp lighting. If the output current is asymmetrical at the current detection point, the control circuit increases the output current to the lamp and continues the frequency heating operation.