Circuit arrangement (10) for operating at least a first and a second LED string, comprising: - a
rectifier (14) having a first (14a) and a second
rectifier terminal (14b) for
coupling to an AC
voltage source (12) or a
DC voltage source (11), and a third (14c) and a fourth
rectifier terminal (14d) for providing a rectifier output
voltage (Urect); - a
voltage equalisation longitudinal impedance (24); - at least one first (100) and one second load subgroup (200), each having a first (102, 202) and a second terminal (104, 204), wherein a bridging element (120, 220) is connected between the first and the second terminal, and each having a
coupling element (110, 210) designed as a four-pole with a first (106, 206) and a second primary terminal (108, 208), as well as with a first (112, 212) and a second secondary terminal (114, 214), wherein the first primary terminal (106, 206) is electrically connected to the first terminal (102, 202) and the second primary terminal (108, 208) is electrically connected to the second terminal (104, 204), wherein the first LED string (D100 to D155), which has a first number of LEDs connected in series, between the secondary terminals (112,114) of the
coupling element (110) of the first load subgroup (100) and the second LED string (D200 to D227), which has a second number of LEDs connected in series,is connected between the secondary terminals (212,214) of the coupling element (210) of the second load subgroup (200); , - a control device (20) which is designed to control the bridging elements (120, 220) as a function of a voltage difference between the respectively associated first terminal (102, 202) and an auxiliary
DC voltage source (22) related to the third rectifier terminal (14c), and as a function of a respective LED string voltage which is applied between the first (102, 202) and the second terminal (104, 204) when the respectively associated bridging element (120, 220) blocks a short-circuit current flow between the two terminals (102, 104, 202, 204); - wherein the second terminal of a higher load subgroup, which is not a lowest load subgroup, is electrically connected to the first terminal of a next lower load subgroup, wherein the first terminal of a highest load subgroup is electrically coupled to the fourth rectifier terminal (14d) and the
voltage compensation longitudinal impedance (24) is connected between the second terminal of a lowest load subgroup and the third rectifier terminal (14c); - a
voltage divider device (26) connected between the third (14c) and the fourth (14d) rectifier terminal for providing a
control signal (28) to the
voltage compensation series impedance (24), wherein the
voltage divider device (26) is designed to control a current with a current value (Ireg) as a function of an instantaneous value of the rectifier output voltage (Urect) through the series-coupled load subgroups (100, 200) by means of the
control signal (28);characterized in that the control device (20) is designed, when the circuit arrangement (10) is operated on a
DC voltage source (11), to permanently control at least a first bridging element of the bridging elements of the load subgroups into a short-circuit state and to permanently control at least a second bridging element of the bridging elements of the load subgroups into a state in which the second bridging element blocks a short-circuit current flow between the first and the second terminal of the associated load subgroup.;