The invention is related to a driving circuit that provides an operating current for at least one lighting means. The driving circuit comprises an isolated switched converter having a switch (4) controlled by a control circuit (10), wherein a primary side choke (3) is charged when the switch (4) is in its conducting state and the primary side choke (3) is discharged when the control circuit (10) controls the switch (4) in its non-conducting state. The circuit comprises first determining means (13) for monitoring the current through the primary side choke (3), and second determining means (11) for determining a switch-off time, wherein the second determining means (11) comprises an auxiliary winding (12) coupled to a secondary side choke (6) and the second determining means (11) is configured to monitor the voltage across the auxiliary winding (12) for determining a switch-off time.