A digital multiplexing and real-time refresh dimming control circuit used in LED driver for multiple LED strings

This paper presents a digital dimming control circuit used in a light-emitting diode (LED) driver, allowing it to dim multiple LED strings with only two input ports which receive serial data accompanied with synchronous clock. A multiplexing technique is used to simplify the control circuit, using one DAC to transfer all the dimming messages for each string, and a real-time refresh technique is used to make the transferred dimming voltage keep a high accuracy all the time. The circuit is friendly compatible with the linear current regulator and pulsewidth modulation (PWM) dimming methods. To get a precise dimming control, we build a 10-bit segment R-2R DAC. The simulation results show the dimming voltages for each LED string keep the errors less than 0.5LSB compared with the designed voltages.