A Digital boost converter to drive white LEDs

A constant off-time boost converter with digital control was proposed and implemented with a field-programmable-gate-array (FPGA) to power white light emitting diodes (WLEDs) for hand-held applications. In the application, a lithium-ion battery with voltage ranging from 3.3 V to 4.2 V was used to light a serial connection of 4 WLEDs drawing current levels from 2 mA to 20 mA. A constant off-time digital PWM controller was chosen to increase the dimming resolution. For the compensator design, a small-signal control model for the constant off-time converter was presented. A digital PI compensator with programmable gain was used to stabilize the control loop for different LED current levels.Experimental results are presented. Same design considerations apply to other applications if a digitally-controlled boost or buck/boost converter with high conversion gain is used.