A DC-DC converter of the voltage reduction-buck type comprising: a direct current source (Vin); an ON-OFF-controllable main switching device (Qx); a main coil (Lx), wherein the main coil (Lx) and the main switching device (Qx) are provided on a line of the direct current source (Vin) next to one another; a fly-wheel diode (Dx) which is arranged such that the induction current of the main coil (Lx) flows through it when the main switching device (Qx) is shifted into the OFF state; a smoothing capacitor (Cx) for smoothing the output of the main coil (Lx); and an auxiliary transformer (Tw) with a primary winding (Pw) and a secondary winding (Sw), wherein the primary winding (Pw), the direct current source (Vin), the main switching device (Qx) and the fly-wheel diode (Dx) are connected in one closed loop, and the secondary winding (Sw), a resonant capacitor (Cw) and an ON-OFF-controllable auxiliary switching device (Qw) form a closed loop, an antiparallel diode (Dqx) is connected in parallel to the main switching device (Qx), and an antiparallel diode (Dqw) is connected in parallel to the auxiliary switching device (Qw), wherein the winding direction of the secondary winding of the auxiliary transformer (Tw) is such that a current begins to flow via the antiparallel diode (Dqw) connected parallel to the auxiliary switching device (Qw) when the main switching device (Qx) is shifted into the OFF state, wherein the DC-DC converter is configured to control the auxiliary switching device (Qw) so as to be shifted into the ON state within a given time (τxx) after the main switching device (Qx) has been shifted into the OFF state; wherein the DC-DC converter is configured to control the main switching device (Qx) and the auxiliary switching device (Qw) such that they are alternatively shifted into the ON state, and wherein the DC-DC converter is configured to control the main switching device (Qx) so as to be shifted into the ON state a predetermined amount of time (τy) after the auxiliary switching device (Qw) has been shifted into the OFF state and within a given time (τzz) after the auxiliary switching device (Qw) has been shifted into the OFF state. a direct current source (Vin); an ON-OFF-controllable main switching device (Qx); a main coil (Lx), wherein the main coil (Lx) and the main switching device (Qx) are provided on a line of the direct current source (Vin) next to one another; a fly-wheel diode (Dx) which is arranged such that the induction current of the main coil (Lx) flows through it when the main switching device (Qx) is shifted into the OFF state; a smoothing capacitor (Cx) for smoothing the output of the main coil (Lx); and an auxiliary transformer (Tw) with a primary winding (Pw) and a secondary winding (Sw), wherein the primary winding (Pw), the direct current source (Vin), the main switching device (Qx) and the fly-wheel diode (Dx) are connected in one closed loop, and the secondary winding (Sw), a resonant capacitor (Cw) and an ON-OFF-controllable auxiliary switching device (Qw) form a closed loop, an antiparallel diode (Dqx) is connected in parallel to the main switching device (Qx), and an antiparallel diode (Dqw) is connected in parallel to the auxiliary switching device (Qw), wherein the winding direction of the secondary winding of the auxiliary transformer (Tw) is such that a current begins to flow via the antiparallel diode (Dqw) connected parallel to the auxiliary switching device (Qw) when the main switching device (Qx) is shifted into the OFF state, wherein the DC-DC converter is configured to control the auxiliary switching device (Qw) so as to be shifted into the ON state within a given time (τxx) after the main switching device (Qx) has been shifted into the OFF state; wherein the DC-DC converter is configured to control the main switching device (Qx) and the auxiliary switching device (Qw) such that they are alternatively shifted into the ON state, and wherein the DC-DC converter is configured to control the main switching device (Qx) so as to be shifted into the ON state a predetermined amount of time (τy) after the auxiliary switching device (Qw) has been shifted into the OFF state and within a given time (τzz) after the auxiliary switching device (Qw) has been shifted into the OFF state.