Abstract: A control device for regulating the output voltage of a voltage regulator wherein the output from that regulator would normally be variable includes inputting that voltage to the control device. There are two overlapping bands which define an effective bandwidth between the upper limit of the lower band and lower limit of the upper band. The output of the device provides a signal responsively regulated in the effective bandwidth such that the output from the regulator can be similarly regulated. In power generation systems a narrow bandwidth can be effectively maintained to permit narrow variations of voltage. A micro-processor facilitates changing the regulated levels for the control device such that the output from the control device can be selectively and controllably changed as desired.