This paper presents the design and implementation of a three-phase unity-power-factor single-stage ac-dc converter based on an interleaved flyback topology. The primary market target of the converter is within the telecommunications industry where it supplies high-quality dc power to the telecom loads and performs high-capacity battery charging while providing zero harmonic emission and unity power factor to the utility grid. The main design objective is to produce the lowest cost within a small-size system. The study includes mathematical analysis and simulation steps where the optimum number of cells to be interleaved and the associated phase shifts among the cells are determined while the emphasis being on the design of a perfectly coupled flyback transformer. Design of a transformer with the lowest leakage inductance and selection of components providing the lowest parasitic effects are critical for obtaining high efficiency and good performance. After the design is verified through simulation studies that uses Simulink and piecewise linear electrical circuit simulation model (PLECS) of the converter, a full-scale prototype is implemented to evaluate the performance of the design. In conclusion, experimental results demonstrate that converter works successfully and meets the commercialization expectations.