The NCP1615 is a high voltage PFC controller designed to drive PFC boost stages based on an innovative Current Controlled Frequency Foldback (CCFF) method. In this mode, the circuit operates in critical conduction mode (CrM) when the inductor current exceeds a programmable value. When the current is below this preset level, the NCP1615 linearly decays the frequency down to a minimum of about 26 kHz at the sinusoidal zero−crossing. CCFF maximizes the efficiency at both nominal and light load. In particular, the standby losses are reduced to a minimum. Innovative circuitry allows near− unity power factor even when the switching frequency is reduced. The integrated high voltage start−up circuit eliminates the need for external start−up components and consumes negligible power during normal operation. Housed in a SOIC−14 or SOIC−16 package, the NCP1615 incorporates the features necessary for robust and compact PFC stages, with few external components.