Control scheme for decoupling auxiliary power supply in dimmable LED drivers

Integrating an auxiliary (AUX) power supply into LED drivers is a popular trend to facilitate LED luminaire system design and reduce system cost and complexity. This AUX power supply can be used to power LED fixture cooling, lighting controller or other suitable electronic devices. In this paper, a cost effective architecture based on Flyback topology is proposed for both constant current (CC) output for LED drive and constant voltage (CV) output for AUX supply. A novel nonlinear ramp based control scheme is invented to decouple the main CC power train from the CV AUX supply and avoid LED output flickering. Small signal modeling is presented to highlight the advantages of this control scheme over conventional peak current mode control. This scheme has been implemented successfully for a 40W dimmable LED driver with a 12V 3W AUX supply.