Circuit Arrangement and Method for Operating a Discharge Lamp

A circuit arrangement for operating a discharge lamp (LA) with

• an inverter, which is designed to provide a signal (SD) with a predeterminable frequency at its output;
• at least one terminal for the discharge lamp (LA),
• at least one lamp inductor (LD), which is coupled between the output of the inverter and the at least one terminal for the discharge lamp (LA);
• at least one capacitor (C1), which is coupled to the lamp inductor (LD);
• a drive apparatus (18) for driving the inverter with the signal (SD) with the predeterminable frequency;
• a control apparatus (10, 12, 14, 16) for controlling a control parameter, which is dependent on the lamp current (IL), to a predeterminable value as a result of a change in the predeterminable frequency, the control apparatus (10, 12, 14, 16) having a first time constant;
• the discharge lamp (LA) having a second time constant, with which it reacts to a change in the predeterminable frequency with a change in a parameter which is dependent on the lamp current (IL);
• the circuit arrangement, owing to the temperature-dependent UI characteristic of the discharge lamp (LA) and the frequency-dependent UI characteristic of a resonant circuit, which comprises at least the capacitor (C1) and the lamp inductor (LD), having at least one range with a first and a second stable working point and, between the first and the second stable working point, an unstable working range in the family of UI characteristics,
• characterized
• in that the first time constant is greater than or equal to the second time constant;
• and
• the drive apparatus (18) is designed to vary the predeterminable frequency during the operation of the discharge lamp (LA) in such a way that the circuit arrangement is operated in the unstable working range.