Circuit for the generation of two symmetrical buses of tension with respect to the negative of the feeding tension, comprising supply means able to supply a power step-up circuit comprising an inductor, a switch, a diode and a condenser, an LC filter being arranged in cascade to said power step-up circuit, a pair of switches with relevant re-circulation diodes being connected in cascade to said LC filter, whose peculiar aspect is that said supply means comprise a single supply source, and a circuit branch consisting of a condenser and a diode connected in series the one to the other and in parallel to said switch and said condenser of said power step-up circuit, a further inductor with diode in series being connected between the anode end of said circuit branch diode and a condenser connected symmetrically with respect to the condenser of said power step-up circuit.