DC-DC converter and method for operating same

A DC-DC converter, comprising:

• an inverter having four primary semiconductor switches interconnected to form an inverter full-bridge for converting a DC input voltage into an AC voltage,
• a transformer constructed as an air gap transformer and comprising a primary winding arranged in a bridge branch of the inverter full-bridge and a secondary winding,
• a rectifier connected to the secondary winding for rectifying a secondary voltage of the transformer,
• a clamping assembly comprising an additional semiconductor switch and a clamping capacitor connected in series with the additional semiconductor switch, with the rectified secondary voltage of the transformer applied to the clamping assembly, and
• a control unit configured to control the primary semiconductor switches and the additional semiconductor switch such that
• the inverter generates an AC voltage which alternatingly assumes an upper voltage level during a first active phase and a lower voltage level during a second active phase,
• the transformer is operated between two successive active phases in a freewheeling phase in which the primary winding is short-circuited,
• the clamping assembly is switched off by the additional semiconductor switch following a start of each freewheeling phase and switched on again after a start of each first or second active phase,
• wherein a switching-off delay duration for switching off the clamping assembly following the start of a freewheeling phase is used as a control variable for regulating a primary current, which flows during the freewheeling phase as a primary freewheeling current through the primary winding of the transformer, to a target value,
• wherein the target value of the primary freewheeling current is determined in dependence of a DC input voltage and/or an output current of the DC-DC converter.