This paper proposes a pre-regulator boost converter applied to a dc/dc converter in order to provide power factor correction. The combination of both stages results in a symmetrical switched power supply, which is composed of two symmetrical stages that operate at 100 kHz, as the individual output voltages are equal to +200 V_dc and -200 V_dc, the total output voltage is 400 Vdc and the total output power is 500 W. The power factor correction IC UC3854 is employed in the control strategy of the boost stage.