LED BIAS CURRENT CONTROL USING ADAPTIVE FRACTIONAL CHARGE PUMP

摘要

A charge pump provides a multiplication factor of 4/3 by using a three-phase mode of operation. In a first mode, first and second capacitors are charged from an input voltage while a third capacitor drives the output voltage based on stored charge in the third capacitor. In a second mode, the voltage potential across the first capacitor is added to the input voltage to generate the output voltage. In a third mode, the voltage potential across the first capacitor is subtracted from the sum of the input voltage and the voltage potential across the second capacitor to generate the output voltage. Operated in this manner, the first, second, and third capacitors will provide the desired 4/3x voltage multiplication. This relatively low multiplication factor can be beneficial in applications such as white LED driver circuits, particularly where the input voltage is provided by a battery.