A control circuit for a DC voltage supply is provided that includes a circuit, an error amplifier and modulator. The circuit is operable to measure a voltage difference between a negative voltage rail and a ground reference in the DC voltage supply. The circuit is further operative to create an offset voltage proportional with the measured voltage difference. The circuit is further yet operative to add the offset voltage to a reference voltage to create a modified reference voltage. The error amplifier has a first input coupled to receive the modified reference voltage and a second input coupled to a positive voltage rail in the DC voltage supply. The error amplifier further has an output. The modulator is coupled to the output of the error amplifier. The modulator is operative to maintain the positive rail at a select value corresponding to the modified reference voltage.