The NCP1651 is an active power factor correction controller that is designed for operation over the universal input range (85 VAC- 265 VAC)in 50/60 Hz power systems. It provides a low cost, low component count solution for isolated ac- dc converters with mid- high output voltage requirements and eases the task of meeting the IEC1000-3-2 harmonic requirements for converters in the range of 50W - 250W.The NCP1651 is a fixed frequency controller that drives a flyback converter topology to operate in continuous/discontinuous mode. It programs the average input current to follow the line voltage in order to provide unity power factor. By using an average current mode control CCM algorithm, the NCP1651 can help provide excellent power factor while limiting the peak primary current. Its fixed frequency operation simplifies the design of the input filter.The NCP1651 uses a proprietary multiplier design that gives much more accurate operation than conventional analog multipliers.