A power converter includes a pair of switches, each of the switches being connected between positive and negative constant DC voltage sources and a common output node which is connected to a load. A modulator opens and closes the switches in a sequence in which the electrical currents controlled by the switches are in opposition to one another at the common output node, and are summed at the output node. The modulator includes a triangle wave generator and comparators which are connected to an error amplifier to provide a bearing switching voltage to the comparators. The comparators switch the control switches in response to the triangle wave generated by the tiangle wave generator increasing above and decreasing below the reference levels. Underlap and overlap of the converter is controlled by varying of the DC bias level of the triangle wave.