An Analog/Digital Controller for LED Drivers

Abstract

A two-loop control scheme for LED drivers is proposed. The analog controller provides the output voltage regulation to the switch mode power converter while the digital controller injects a control signal to affect a change for the analog controller to implement an efficient constant current load. The proposed analog and digital control scheme is implemented for a two-string LED driver. The driver increases its efficiency by maintaining a minimum drive voltage across parallel-connected multiple LED strings to maintain the LED string current constant. Phase shifted PWM dimming (PSPWM) is implemented in order to reduce load current variations, improve EMI, and increase system efficiency. A mathematical model for merging the analog and digital controllers is implemented. The proposed LED driver was simulated using MATLAB SIMULINK and experimentally verified using a two-string LED load with three white LEDs in each string.