Abstract: An amplitude-regulated, distortion-free sine wave voltage source capable of operating from input sine waves, square waves or quasi-square waves, this ferroresonance-simulating inverter apparatus includes a special control winding and shorting switch therefor that is cyclically operated by a control circuit. By varying the point of time during each half cycle at which the control winding becomes short circuited in accordance with cyclic comparisons being made between recurring voltage ramps and an error signal related to system output voltage level, a feedback loop is provided to regulate such output voltage. The transformer secondary is not required to operate in the saturated mode through use of a ferroresonant capacitor in the usual manner, but the effect of ferroresonance is simulated to achieve regulation through the shunting of flux to saturate separate core shunts in a small fraction of the total core.