US005945788A [ii] Patent Number: [45] Date of Patent:
[54] ELECTRONIC BALLAST WITH INVERTER CONTROL CIRCUIT
[75] Inventors: Edward Li, Roselle; Guang Liu, Lake Zurich; Anand K. Upadhyay, Libertyville; Dennis L. Stephens,
Barrington, all ol 111.
[73] Assignee: Motorola Inc., Schaumburg, 111.
[21] Appl. No.: 09/050,829 [22] Filed: Mar. 30, 1998
[51] Int. CI. G05F 1 00
[52] U.S. CI 315/308; 315/291; 315/224;
315/127; 315/DIG. 5; 315/DIG. 7
[58] Field of Search 315/308, 307,
315/224, 225, 209 R, 291, 293, 312, 314, 316, 324, 360, 362, DIG. 4, DIG. 7, 127,
244
[56] References Cited
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Primary Examiner—Haissa Philogene
Attorney, Agent, or Firm—Kenneth D. Labudda
[57] ABSTRACT
An electronic ballast (300) for powering at least one gas discharge lamp (10) includes an inverter (400), an output circuit (700), a lamp lault detection circuit (800), and an inverter control circuit (500). Ballast (300) operates according to an inverter control method (100) that includes repeating a filament preheating step and a frequency shifting step up to a predetermined number of times in order to facilitate lamp ignition under low-temperature conditions and to verify the legitimacy of a lamp fault. Inverter control circuit (500) is well-suited for implementation as a custom integrated circuit. Ballast (300) optionally includes an overcurrent detection circuit (820') with an adjustable lamp fault detection threshold that provides decreased sensitivity during lamp starting and enhanced protection after lamp ignition.
31 Claims, 8 Drawing Sheets
