Method and apparatus for driving LEDs
US6836157B2 · kind B2 · utility
Assignee
Inventors
Key dates
| Filing date | May 9, 2003 |
| Grant date | Dec 28, 2004 |
| Priority date | — |
| Expiry date | Jul 15, 2023 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG09G2330/021
- WIPO fieldElectrical machinery, apparatus, energy
- WIPO sectorElectrical engineering
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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.