The SCR chopper circuit has a very wide range of application in regulating a dc power, and its merits are universally appreciated. Because of its merits, the circuit is most suitable for a nonfailure power source that supplies power from a set of rectifier-batteries to a communication equipment or any other electronic equipment, which requires a dc power source of several output voltages. For such purposes, the output voltage of the circuit should be smooth, accurately regulated, and should respond quickly; at the same time, the efficiency must be high and reliability excellent. This paper offers, firstly, some improvements on the Morgan circuit in order to make it peculiarly suitable for different kinds of practical applications; namely, the smoothing filter is made as small as possible to make the response of the circuit rapid, while the efficiency is kept high. Secondly, data, obtained through the analysis of the operation in the case of the small filter, are presented. Thirdly, the paper shows, as the result of such analysis, that if a saturable current transformer (SCT) is designed properly, the circuit will behave as a self-regulating constant voltage power source. Lastly, it proposes a practical application which has a suitable protecting circuit composed of some simple circuit elements providing against the failure of commutation which causes a severe overvoltage and overcurrent to the load.