Fast dynamics current control of DCM flyback as PFC front converter for lighting applications

Most common Power Factor Correction (PFC) solutions for low power applications, when galvanic isolation is required, involve the use of discontinuous conduction mode (DCM) dc to dc topologies. The control is generally based on fixed duty ratio operation, or at best, on a classic low-bandwidth duty-ratio control. Considering public lighting systems, in which a high number of low power converters are connected into a single power line, the transient response of the full system is critical for keeping the power line balanced without affecting the rest of the grid. Furthermore, at each ballast, the second stage needs also to operate independently upon such variations. This paper proposes a simple high bandwidth control technique for a PFC Flyback converter acting as front converter of a LED lighting system, that also reduces the harmonic content of the AC line current. The control scheme is discussed and implemented, and experimental results are presented.