Design of LED driver using digital up/down counter

A novel digital-controlled switch mode LED driver is presented, consisting of a digital up/down counter, a binary-to-PWM (pulse-width-modulation) converter, a comparator, and switching devices. The digital counter is a substitution of an error amplifier in a normal LED driver or a DC-DC converter. This counter increases or decreases its binary value, according as the output of the comparator is high or low. Then the binary value would be converted to a PWM signal which has a duty ratio proportional to the binary value and controls the switching devices. This is a novel digital-control algorithm for the proposed LED driver. We successfully verify the proposed digital-control algorithm using a test board which consists of a digital controller or a CPLD (complex programmable logic device) and several discrete devices such as a comparator, a transistor, and a Schottky barrier diode. And then, we design the novel LED driver through a 0.35μm 2-poly 4-metal 40V process.