Hybrid serial-output converter topology for volume and weight restricted LED lighting applications

This paper introduces a new high power density step-up LED driver converter architecture based on power processing divided between a switched capacitor (SC) converter and a flyback stage. The step up function is obtained by stacking the output of the flyback on top of the SC converter output. The high power density SC processes the majority of the power of the system and is left unregulated to maximize its efficiency. The small flyback processes only a small portion of the total power and regulates the output voltage. As a result high power efficiency, small converter volume, and tight output voltage regulation are achieved. A digital controller regulates the operation of this hybrid converter topology. In comparison with conventional boost and flyback based solutions, the new architecture drastically reduces the passive component volume and decreases peak voltage stress of switches. The paper also gives design guidelines for this topology and topologies of its kind for a given power processing efficiency target. Experimental results obtained with a 12 V to 55 V, 47 W, 500 kHz prototype show that the hybrid converter has about four times smaller energy storage requirements compared to conventional solutions, while maintaining approximately the same power processing efficiency of 90%.