The ISL1904 is a high-performance, critical conduction mode (CrCM), flyback controller used for single-stage conversion of the AC mains to a constant current source with power factor correction (PFC). The controller regulates the output current by monitoring the primary side switching current so the feedback signal does not cross the isolation barrier. Operation in CrCM allows near zero-voltage quasi-resonant switching (ZVS) for improved efficiency while maximizing magnetic core utilization. The ISL1904 LED driver provides all of the features required for high-performance dimmable LED ballast designs and supports AC or DC input, isolated or non-isolated flyback and boost topologies. This advanced BiCMOS controller features all of the functions required to design low cost low parts count LED driver.