Abstract: A boost-input backed-up uninterrupted power supply provides an uninterrupted output voltage to a load. The backed-up power supply has an input rectifier and filter for converting an input voltage source voltage into at least an unregulated positive dc voltage source, and an unregulated negative dc voltage source. Batteries provide respective positive and negative battery voltages at corresponding positive and negative battery output terminals. A diode isolates the unregulated positive and negative dc voltage sources from their respective battery voltages for unregulated voltage source values equal to or greater than their respective battery voltages and clamps the unregulated dc voltage values to their respective battery voltages in response to loss of the sinusoidal input voltage source. A pair of boost regulators receives power from the unregulated positive and negative dc voltage sources and provide positive and a negative regulated dc voltage with respect to the return.

Abstract: An uninterruptible power supply comprising a regulating transformer including output circuitry for connection to a load, first input circuitry for coupling a reserve AC voltage source to the regulating transformer and second input circuitry for coupling a primary AC voltage source to the regulating transformer, the second input circuitry comprising a plurality of winding taps, with each of the taps including a tap switch coupled to the primary AC voltage source.The uninterruptible power supply also includes a voltage control monitor for monitoring the voltage of the primary source and, if the voltage is outside a predetermined maximum allowable range, opening all of said tap switches to isolate the primary source from said transformer, and, if said voltage is within said predetermined maximum allowable range, selectively closing one of said tap switches so that the voltage at the load is held within a predetermined range.