Patent ID: 7397196

Claim:
Circuit arrangement for operating a lamp equipped with input terminals for connection to the poles of a supply voltage source, a first series arrangement comprising a first switching element shunted by a first diode and a second switching element shunted by a second diode and connecting the input terminals, a second series arrangement comprising a third switching element shunted by a third diode and a fourth switching element shunted by a fourth diode and connecting the input terminals, a load circuit connecting a terminal between the first and the second switching element with a terminal between the third and the fourth switching element and comprising a series arrangement of an inductor L 1 , terminals for lamp connection and an inductor L 2 , a control circuit coupled to control electrodes of the switching elements and comprising circuitry for controlling the circuit arrangement in a first operating state in which the fourth switching element is maintained in a conductive state while the first switching element is rendered alternately conductive and non-conductive at a high frequency, and for controlling the circuit arrangement in a second operating state in which the third switching element is maintained in a conductive state while the second switching element is rendered alternately conductive and non-conductive at a high frequency, and for alternating the operating state of the circuit arrangement between the first and the second operating state at a low frequency, a capacitor C 1 coupled with a first end to a terminal of the load circuit between the inductor L 1 and a terminal for lamp connection, characterized in that a second end of the capacitor C 1 is coupled to an input terminal, and in that the control circuit comprises circuitry for controlling the circuit arrangement in a third operating state, in which the first and third switching element are operated in such a way that at least one of these switching elements is rendered alternately conductive and non-conductive at a high frequency, during a time interval between subsequent operation in the first and the second operating state, and for controlling the circuit arrangement in a fourth operating state, in which the second and fourth switching element are operated in such a way that at least one of these switching elements is rendered alternately conductive and non-conductive at a high frequency, during a time interval between subsequent operation in the second and the first operating state.