Patent ID: 8450934

Claim:
A circuit arrangement for operating a low-pressure discharge lamp, the circuit arrangement comprising: a voltage source with two terminals; switches; and a series resonant circuit, which comprises an inductive element which is coupled to an electrode of the low-pressure discharge lamp, and which comprises at least one capacitive element which is connected in series with the inductive element and in parallel with the low-pressure discharge lamp; a controller configured to control the switches in such a way that an AC voltage is applied to the series resonant circuit; a PTC thermistor, which is coupled on one side to a circuit point of the series resonant circuit and on the other side to, at least one of: a) the cathode of a second diode, the anode of the second diode being coupled to the second terminal of the voltage source and b) the anode of a first diode, the cathode of the first diode being coupled to the first terminal of the voltage source; the circuit arrangement further comprising a resistive element connected in series with the second diode in the circuit between one of the terminals of the voltage source and the PTC thermistor; and an evaluation device configured to tap off the voltage drop across the resistive element and being coupled to the controller in order to deactivate the controller.