Converter for a luminous means (3; 5) comprising - a primary-side circuit (20; 50; 90) having a half-bridge circuit comprising two reciprocally-clocked switches (21; 22) and an LLC resonant circuit (25-27), wherein a first switch of the two reciprocally-clocked switches is connected between a supply terminal (Vbus) of the primary-side circuit (20; 50; 90) and the LLC resonant circuit (25-27), and wherein a second switch of the two reciprocally-clocked switches is connected between the LLC resonant circuit (25-27) and a reference voltage, - a secondary side having an output for the power supply of the lighting means (3; 5) and that is galvanically isolated from the primary-side circuit (20; 50; 90), and - a control device , wherein the control device is designed to control the first switch of the half-bridge circuit and the second switch of the half-bridge circuit, wherein the control device is further designed to detect a deviation at the output of the secondary side as a function of a phase position of a current (52; 73) in the primary-side circuit (20; 50; 90), characterized in that - the primary-side circuit (20; 50; 90) is designed to tap a voltage across a measuring resistor connected between the second switch of the half-bridge circuit and the reference potential, in order to detect the current (52; 73) when the first switch is switched to an off state, and the second switch is switched to an on state, and - the control device is designed to detect the deviation through the phase position of the current (52; 73) as a function of a time (TN) of a zero crossover of the current (52; 73), wherein the control device is designed to detect a deviation between the time (TN) of the zero crossover and a reference time (TM), and to detect the deviation as a function of a threshold comparison of the deviation. - a primary-side circuit (20; 50; 90) having a half-bridge circuit comprising two reciprocally-clocked switches (21; 22) and an LLC resonant circuit (25-27), wherein a first switch of the two reciprocally-clocked switches is connected between a supply terminal (Vbus) of the primary-side circuit (20; 50; 90) and the LLC resonant circuit (25-27), and wherein a second switch of the two reciprocally-clocked switches is connected between the LLC resonant circuit (25-27) and a reference voltage, - a secondary side having an output for the power supply of the lighting means (3; 5) and that is galvanically isolated from the primary-side circuit (20; 50; 90), and - a control device , wherein the control device is designed to control the first switch of the half-bridge circuit and the second switch of the half-bridge circuit, wherein the control device is further designed to detect a deviation at the output of the secondary side as a function of a phase position of a current (52; 73) in the primary-side circuit (20; 50; 90), characterized in that - the primary-side circuit (20; 50; 90) is designed to tap a voltage across a measuring resistor connected between the second switch of the half-bridge circuit and the reference potential, in order to detect the current (52; 73) when the first switch is switched to an off state, and the second switch is switched to an on state, and - the control device is designed to detect the deviation through the phase position of the current (52; 73) as a function of a time (TN) of a zero crossover of the current (52; 73), wherein the control device is designed to detect a deviation between the time (TN) of the zero crossover and a reference time (TM), and to detect the deviation as a function of a threshold comparison of the deviation. <EOS>