The Supertex HV9120 and HV9123 are Switch Mode Power Supply (SMPS) controller subsystems that can start and run directly from almost any DC input, from a 12V battery to a rectified and filtered 240V AC line. They contain all the elements required to build a single-switch converter except for the switch, magnetic assembly, output rectifier(s) and filter(s). A unique input circuit allows the 912x to self-start directly from a high voltage input, and subsequently take the power to operate from one of the outputs of the converter it is controlling, allowing very efficient operation while maintaining input-to-output galvanic isolation limited in voltage only by the insulation system of the associated magnetic assembly. A 2% internal bandgap reference, internal operational amplifier, very high speed comparator, and output buffer allow production of rugged, high performance, high efficiency power supplies of 50 watts or more, which can still be over 80% efficient at outputs of 1.0W or less. The wide dynamic range of the controller system allows designs with extremely wide line and load variations with much less difficulty and much higher efficiency than usual. The exceptionally wide input voltage acceptance range also allows much better usage of energy stored in input dropout capacitors than with other PWM ICs. Remote on/off controls allow either latching or nonlatching remote shutdown. During shutdown, power required is under 6.0mW.