LED converter, comprising: - a resonant converter with a switching regulator comprising switching regulator switches (HS, LS), preferably a clocked half-bridge converter, - a galvanic barrier, the primary side of which being supplied by the switching regulator and the secondary side of which being arranged for providing directly or indirectly power to terminals for connecting one or more LEDs, - a control circuit (PCC2, PCC3) on the primary side of the galvanic barrier of the resonant converter, - a sensing means on the secondary side of the galvanic barrier sensing a secondary side electric parameter indicative of an LED string, when the LED string is connected to said terminals, - a feedback path from the sensing means (R L) to the control circuit (PCC2, PCC3) adapted to feedback the secondary side electric parameter from the secondary side of the galvanic barrier to the primary side of the galvanic barrier, - wherein the secondary side electric parameter is the output voltage of the resonant converter, characterized in that - in case no LED string is connected to the LED converter, the control circuit (PCC2, PCC3) is adapted to cyclically control a switching frequency of the switching regulator switches (HS, LS) of the switching regulator, in particular switches of a clocked half-bridge, from a high frequency to a lower frequency, and to monitor whether the output voltage of the resonant converter reaches a predetermined threshold value, wherein the output voltage of the resonant converter on the secondary side will raise to the predetermined threshold value, when no LED string is connected, and - the control circuit (PCC2, PCC3) is adapted to detect that an LED string is connected when during the controlling of the frequency from the high frequency to the low frequency the output voltage of the resonant converter does not reach the predetermined threshold value. - a resonant converter with a switching regulator comprising switching regulator switches (HS, LS), preferably a clocked half-bridge converter, - a galvanic barrier, the primary side of which being supplied by the switching regulator and the secondary side of which being arranged for providing directly or indirectly power to terminals for connecting one or more LEDs, - a control circuit (PCC2, PCC3) on the primary side of the galvanic barrier of the resonant converter, - a sensing means on the secondary side of the galvanic barrier sensing a secondary side electric parameter indicative of an LED string, when the LED string is connected to said terminals, - a feedback path from the sensing means (R L) to the control circuit (PCC2, PCC3) adapted to feedback the secondary side electric parameter from the secondary side of the galvanic barrier to the primary side of the galvanic barrier, - wherein the secondary side electric parameter is the output voltage of the resonant converter, characterized in that - in case no LED string is connected to the LED converter, the control circuit (PCC2, PCC3) is adapted to cyclically control a switching frequency of the switching regulator switches (HS, LS) of the switching regulator, in particular switches of a clocked half-bridge, from a high frequency to a lower frequency, and to monitor whether the output voltage of the resonant converter reaches a predetermined threshold value, wherein the output voltage of the resonant converter on the secondary side will raise to the predetermined threshold value, when no LED string is connected, and - the control circuit (PCC2, PCC3) is adapted to detect that an LED string is connected when during the controlling of the frequency from the high frequency to the low frequency the output voltage of the resonant converter does not reach the predetermined threshold value.