US 6,982,528 B2
Thermal protection for lamp ballasts
David E. Cottongim, Sellersville, Pa. (US); Jecko Arakkal, Emmaus, Pa. (US); Venkatesh Chitta, Center Valley, Pa. (US); and Mark S. Taipale, Harleysville, Pa. (US)
Assigned to Lutron Electronics Co., Inc., Coopersburg, Pa. (US)
Filed on Nov. 12, 2003, as Appl. No. 10/706,677.
Prior Publication US 2005/0099142 A1, May 12, 2005
Int. Cl. G05F 1/00 (2006.01); H01H 5/04 (2006.01)
U.S. Cl. 315—309 47 Claims
OG exemplary drawing
 
1. A circuit for controlling output current from a ballast to a lamp comprising:
a) a temperature sensing circuit thermally coupled to the ballast to provide a temperature signal having a magnitude indicative of ballast temperature, Tb, and
b) control circuitry capable of causing the ballast to enter a current limiting mode when the magnitude of the temperature signal indicates that Tb has exceeded a predetermined maximum desired ballast temperature, T1;
wherein the control circuitry reduces the output current in response to the temperature signal according to one of (i) a step function or (ii) a combination of step and continuous functions, while continuing to operate the ballast.