If the voltage of rectangular waveform produced in the inverter is used as a dc power supply through a half-wave rectifier, a smoothing capacitor and reactor can be made extremely small by using asymmetric two phase system. Although this basic concept has been already reported, the basic operation of the amplitude modulation converter, used in this system as a key element, has not been clarified yet. In this paper, we discuss the output voltage and the efficiency as a function of duty ratio and output current, on the typical amplitude modulation converter of single phase