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:
Jan. 19, 2010
Filed:
Mar. 27, 2007
Brant Ture Johnson, Concord, MA (US);
James Henry Aliberti, North Attleboro, MA (US);
Brant Ture Johnson, Concord, MA (US);
James Henry Aliberti, North Attleboro, MA (US);
Texas Instruments Incorporated, Dallas, TX (US);
Abstract
A current source generates, with high efficiency, a current that is substantially constant over a wide range of output voltages. This current is injected into the first end of a series-connected string of LEDs, with the second end of the string connected through a resistor to ground. The voltage developed across this resistor, which is a measure of current flow in the series string, is fed back to the current source, wherein feedback maintains nearly constant current output over a wide range of output voltages. A field effect transistor (FET) is placed in parallel with each LED in the string. A level shift gate driver couples a pulse width modulated control signal to the gate of each FET. With the FET being coupled across a particular LED, the LED can be bypassed when the FET is actuated or receive current when the FET is deactuated. By modulating the duty cycle of each FET, the brightness of each associated LED may be varied smoothly over its full range.