The buck converter is generally utilized in many applications because of various advantages like maintaining high efficiency for the wide range of input voltage, cost reduction, low output voltage, protection against inrush current and lifetime improvement. However, when on-time of buck converter is kept constant, the input voltage and current remains out of phase that cause’s low PF and high total harmonic distortion (THD). Therefore a power factor improvement technique is implemented in this paper that permits the average input current sinusoidal without need of extra converter to work in cascade with buck converter. The critical conduction mode (CRM) buck converter operating with constant on-time (COT) control scheme have low PF because of harmonic contained input current waveform. So in order to make the input current waveform as a sinusoidal by changing the on-time of buck switch, a variable-on-time (VOT) control scheme for CRM buck converter is proposed in this paper. The theoretical analysis is given, and the simulation results confirm the advantages of the proposed control scheme. The object of the research paper is to propose the control scheme to realize high PF for CRM buck converter by only modulating the on-time of buck switch and without need of extra converter to work with buck converter.