1. ABSTRACT This paper concerns a lossless commutation Buck Pulse-Width-Modulated Converter by using a Resonant Disconnecting Circuit (Buck-LC-PWM-RDC). Operation principle, design oriented analysis and numerical examples simulation and experimental results are presented.The new topology presents a new working mode. This is obtained by using a resonant commutation cell composed by three switches, two capacitors and two inductors. The three switches commutate under zero current, zero voltage and zero current, respectively (Ti, T2 and T3). The most important property of the introduced circuit is the ability to regulate output power and voltage by pulse-width-modulation, with constant operating frequency, without load limitation and without sacrificing the lossless commutation. As a consequence, the time response is improved, the design procedure and implementation