Patent ID: 7557519
Filing Date: 2009-07-07
Classification: H05B

Abstract:
1. An apparatus, comprising: a unidirectionally conductive light-emitting device; an inductive element coupled in parallel to said light-emitting device; a switching element to conduct current from a power supply through said inductive element during an on-time interval and an off-time interval during which said inductive element is discharged through said light-emitting device; and a signal generator coupled to said switching element to switch it between the on-time interval and the off-time interval, wherein said signal generator is configured to determine the duration of the off-time interval from the current though said inductive element, and wherein the signal generator further comprises: a measuring element to measure a duration of the off-time interval, an estimating element, coupled to said measuring element, to produce a first signal representative of an estimated average current through said light-emitting device, a calculating element, coupled to said estimating element, to produce an error signal by subtracting said first signal from a signal representative of said target average current through said light-emitting device, and a controller, coupled to said measuring element and to said subtracting element, to control the duration of the off-time interval.