Power Factor Preregulators (PFP) have been used to improve input current waveform of off-line power supplies. There are two major approaches in implementing control circuits in PFP: the multiplier approach and the voltage-follower approach. The simplest one is the voltage-follower approach because the converter operates in discontinuous conduction mode (DCM), and only one loop control is required. SEPIC and CUK converters present a great advantage over boost and fly-back topologies in DCM: an input current with low harmonic content can be obtained by correctly choosing inductors L, and L, of the converter with a fixed operation frequency, as is demonstrated here. Also some discussion about the intermedium capacitor C, as well some advantages and disadvantages of the aplication is done. Simulation and experimental results support the approach. Therefore, SEPIC and CUK converters in DCM seem to be good choices to use as PFP.