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This paper presents a new scheme for adaptive automatic synchronization of variable high frequency (HF) control pulses with the single phase ac line. The application of this scheme is made for pulsewidth modulation (PWM) control of single-switch, quasi-resonant zero-current-switched (QRZCS), ac-dc converters. The objective is to propose a converter, to improve the performance of dc-drive and input power quality, with minimum complexity. Adaptive pulse synchronizing control scheme gives nonfluctuating dc output voltage for driving dc-motor with low source-current harmonics. Design of passive components, analysis, control and experimental results of proposed dc-drive and its comparison with low frequency (LF) hard-switched dc-drive are given. Experimental results show that the application of the proposed synchronizing control based HF quasi-resonant zero-current switching (QRZCS) converters for dc-drive gives high-power-factor operation, lower harmonic distortion, better transient response and non fluctuating motor speeds.