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. 28, 1999
Filed:
Aug. 07, 1997
John F Steel, Fort Wayne, IN (US);
Bryce L Hesterman, Madison, AL (US);
MagneTek, Inc., Nashville, TN (US);
Abstract
A symmetry control circuit for a ballast driving a gas discharge lamp. The circuit controls the pre-heat time of a gas discharge lamp with heatable filaments by holding off the full striking voltage until the lamp has had sufficient time to pre-heat. The circuit is designed to work with electronic ballasts and especially electronic ballasts without boost power factor correction to properly pre-heat the lamp. A control circuit reduces the duty cycle in an inverter transistor, thereby keeping the voltage across the lamp low while allowing filament heating to occur. The control circuit is disabled after a time interval of about 500 ms, allowing the transistor duty cycle to increase to 50 percent, the lamp voltage to rise, and the properly pre-heated lamp to ignite.