Design of a High Efficiency WLED Driver in 40 nm CMOS Technology

A DC-DC boost-converter-based, three-string White LED (WLED) driver with pure combinational logic in the forward voltage compensation circuit is presented. The proposed architecture optimizes efficiency with the presence of different forward voltage drop across each WLED connected in series in one string and among different strings. The strings don’t even need to be balanced (could have different numbers of WLEDs per string). The efficiency optimization is done via setting the minimum proper voltage (in real-time) at the output of the boost converter that activates all parallel strings and by choosing the appropriate arrangement of strings (number of strings and number of WLEDs in each string). Each string has a constant regulated current of 25 mA to drive the series-connected WLEDs in that string. An efficiency of 88.85 % was achieved with input voltage ranges between 3 V to 3.8 V and output voltage up to 25 V . The circuit is implemented using a 40 nm TSMC CMOS process.