DC-DC converter having a transformer having a primary-side primary coil and a secondary-side secondary coil, wherein the primary coil is connected on one side to a first primary voltage terminal and is connected on the other side, in series with a first switch, to a second primary voltage terminal, wherein, in parallel with the primary coil, a capacitor is connected in series with a second switch, wherein the secondary coil is connected on one side to a first secondary voltage terminal and is connected on the other side, in series with a third switch, to a second secondary voltage terminal, having a regulating device, which is designed to switch the first, second and third switches off and on repeatedly, wherein the first switch is always switched off when the second switch is switched on, and vice versa, for generating an alternating current in the primary coil, and to switch the third switch off and on depending on the switch position of the first switch, characterized in that the regulating device is designed to set a time at which the third switch is switched on to a time before the first switch is switched off and the second switch is switched on in order to enable a power flow on the side of the secondary side to the primary side, to set, depending on a presettable power, the interval of the time at which the third switch is switched on before the time at which the first switch is switched off, wherein the interval is increased as the power to be transmitted increases and is reduced as the power decreases, and to switch the third switch off at its current zero crossing or shortly before its current zero crossing, wherein switching the third switch on increases a current in the secondary coil and switching the first switch off decreases the current in the secondary coil. wherein the primary coil is connected on one side to a first primary voltage terminal and is connected on the other side, in series with a first switch, to a second primary voltage terminal, wherein, in parallel with the primary coil, a capacitor is connected in series with a second switch, wherein the secondary coil is connected on one side to a first secondary voltage terminal and is connected on the other side, in series with a third switch, to a second secondary voltage terminal, having a regulating device, which is designed to switch the first, second and third switches off and on repeatedly, wherein the first switch is always switched off when the second switch is switched on, and vice versa, for generating an alternating current in the primary coil, and to switch the third switch off and on depending on the switch position of the first switch, characterized in that the regulating device is designed to set a time at which the third switch is switched on to a time before the first switch is switched off and the second switch is switched on in order to enable a power flow on the side of the secondary side to the primary side, to set, depending on a presettable power, the interval of the time at which the third switch is switched on before the time at which the first switch is switched off, wherein the interval is increased as the power to be transmitted increases and is reduced as the power decreases, and to switch the third switch off at its current zero crossing or shortly before its current zero crossing, wherein switching the third switch on increases a current in the secondary coil and switching the first switch off decreases the current in the secondary coil.