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:
Dec. 02, 2008
Filed:
Nov. 23, 2004
William E. Rader, Carrboro, NC (US);
Ryan P. Foran, Bullock, NC (US);
William E. Rader, Carrboro, NC (US);
Ryan P. Foran, Bullock, NC (US);
Semtech Corporation, Morrisville, NC (US);
Abstract
A plurality of LEDs is driven in parallel, in at least two modes. In a first mode, the LEDs are driven with a first voltage. In subsequent modes, the LEDs are driven with successively higher voltages. The forward voltage drop for each LED is monitored, and the driver switches from the first mode to successive modes based on the largest of the LED forward voltage drops. The current through each LED is controlled by directing a reference current through a first digitally controlled variable resistance circuit, and directing the LED current through a second digitally controlled variable resistance circuit having substantially a known ratio to the first variable resistance circuit and connected in series with the LED. A digital count is altered based on a comparison of the first and second currents, and the first and second variable resistance circuits are simultaneously altered based on the digital count.