elements s7 s12 is continuously switched on or if sufficient safety times are not maintained this immediately results in a secondary short of the transformer t1 in the exemplary embodiment depicted in fig3 the drive circuit 32 which is designed as a single assembly creates the drive signals not only for the switch elements s1 s4 of the flow converter 24 but also for the switching stages 30 30 39 30 34 for the rectifiers 26 26 39 26 34 it is thereby possible to create all these signals in a perfectly phase coordinated manner and with minimal safety times so that the dc voltage u 3 is especially stable fig1 depicts the four switching signals generated by the drive circuit 32 namely a first drive signal for the switch elements s1 s4 or s5 a second drive signal for the switch elements s2 s3 or s6 a third drive signal for the switch elements s7 s10 or s11 and a fourth drive signal for the switch elements s8 s9 or s12 the first two drive signals are symmetrical rectangular signals shifted 180 u00b0 toward each other with dead times separating their switch on phases the third drive signal corresponds to the first drive signal however additional safety times are therein inserted at the beginning and at the end of the switch.