Analysis and optimization of the AHB-flyback topology for solid state lighting applications

In this paper a single stage AC/DC converter, based on the asymmetrical half bridge (AHB) flyback topology, is proposed as a line fed HBLED lamp ballast. Simplicity and reduced component count, together with high switching frequency operation (300-450kHz), effectively determine significant volume reduction and higher power density with respect to conventional circuits. Moreover, thanks to zero voltage switching and frequency modulation, high efficiency can be achieved, making the proposed topology an attractive solution for HBLED driving. The converter can be designed to operate with a significant input voltage ripple, allowing input filter capacitance reduction and compliance with the EN61000-3-2 standard. Converter operation principles and boundary conditions among the different topological phases have been analyzed. Feed-forward and feedback techniques have been investigated to optimize converter operating conditions, improve efficiency and minimize the current ripple through the lamp. A prototype has been built and tested; experimental results are reported.