Abstract: An uninterruptible power supply utilizes a controlled ferroresonant regulator to derive a regulated DC voltage from a primary AC source. A reserve source of DC power is coupled to the output through a DC voltage regulator which is activated when the DC output voltage of the power supply drops below a predetermined threshold.

Abstract: An uninterruptable power supply supplies a regulated output by utilizing a ferroresonant transformer. Two independent inputs are connected to the transformer; one input is connected to a commercial AC line signal source, the other input is connected to a battery energized static inverter circuit. The AC line source normally supplies the output power. A phase control system monitors the phase of the regulated output signal and constrains the static inverter to run in phase with the output. The phase and magnitude of the AC line signal are monitored. If the magnitude of the AC line drops significantly, the static inverter is constrained to operate in phase with the AC line signal wherein the inverter and AC line both share to contribute power to the output load. If the AC line signal fails, the static inverter operates independently and supplies all of the output power to the load.