Patent ID: 8581519
Filing Date: 2013-11-12
Classification: G09G,H05B

Abstract:
1. A digital-to-analog converter (DAC)-switched light-emitting diode (LED) driver comprising: a DC-DC converter that generates a sum current on a sum node; a first LED path having a first LED and a first DAC in series between the sum node and a supply node; a first digital input to the first DAC, the first digital input for carrying a first digital value, the first DAC generating a first current through the first LED, the first current being a function of the first digital value; a bypass path having a bypass DAC between the sum node and the supply node; a bypass digital input to the bypass DAC, the bypass digital input for carrying a bypass digital value, the bypass DAC generating a bypass current through the bypass path, the bypass current being a function of the bypass digital value; a ramp controller that generates ramp sequences of the bypass digital value, the ramp sequences being gradually increasing or decreasing sequences of the bypass digital value that cause the bypass DAC to gradually increase or decrease the bypass current over a ramp period of time; and switch controller means for abruptly switching the first digital input from a low digital value that causes the first DAC to generate a first current that is insufficient to illuminate the first LED, to a high digital value that causes the first DAC to generate a first current that is sufficient to illuminate the first LED, and for abruptly switching the bypass digital input from a high digital value to a low digital value, wherein the bypass current is gradually ramped up and down when the first current is not causing the first LED to illuminate, and wherein both the first current and the bypass current are abruptly switched when the first LED is illuminated or de-illuminated, wherein the sum current is not abruptly changed, whereby the sum current is gradually ramped but the first current and the bypass current are abruptly switched when the first LED is illuminated.