Abstract: An AC voltage regulator able to provide a desired voltage to any type of a given load within a predetermined range without any output power interruptions during any transition time, without distortion of the AC sine wave and without high current circulating through the circuit components during the voltage switching. The voltage regulator uses a single regulator transformer having a primary winding and a secondary winding. The secondary winding of the regulator transformer is connected in series between a power source and the load, while the primary winding of the regulator transformer is connected with the power source so that the primary and secondary windings have opposite polarities. The position of a plurality of switches can be variably set by the control circuit to control current flow through the primary winding and to provide a normal mode, a step-down mode, or a step-up mode.