A Digital Controller Based on Primary Side Regulation with Improved Accuracy for LED Application

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Abstract
A digital controller for LED driver is presented. The controller is used in the flyback converter which works in discontinuous current mode (DCM). A comparator is adopted to shape the auxiliary winding voltage based on traditional primary side regulation (PSR). A five-states finite state machine (FSM) is designed to deal with the shaped auxiliary winding signal. The FSM extracts the system time information from the shaped signal and controls all the sequences in the whole system. To achieve high accuracy of the output current, an adaptive delay compensation scheme is adopted. A LED prototype whose typical output power is 7 W is used in both simulation and experiment to demonstrate the effectiveness of this novel digital controller. The measurement results show that the line regulation when the input ac voltage varies from 85–265 V is 3.4% and the load regulation when the load varies from 3–10 LEDs is 2.5%.

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