Patent ID: 7190127

Claim:
An electronic ballast for operating a discharge lamp (LA), which has: a converter (V 1 , V 2 ) for producing a radiofrequency AC voltage, an intermediate circuit capacitor (C 6 ) for supplying (UC 6 ) a DC voltage to the converter (V 1 , V 2 ), and a pump circuit (D 6 , C 8 , C 9 , L 1 ), which charges the intermediate circuit capacitor (C 6 ) from the AC voltage of the converter (V 1 , V 2 ), characterized by a voltage limitation circuit (R 8 , R 3 , D 5 , R 4 , R 5 , C 3 , SD), which is connected in parallel with the intermediate circuit capacitor (C 6 ), for limiting the voltage (UC 6 ) across the intermediate circuit capacitor (C 6 ), which has: a series circuit (R 3 , R 8 ) having a dissipation element (R 8 ) and a measuring resistor (R 3 ), a delay circuit (R 4 , R 5 , C 3 ), and a shutdown device (SD), which has a threshold value element (DZ 3 ), which defines a switching voltage (UC 3 ) across the delay circuit (R 4 , R 5 , C 3 ), and whose output signal deactivates the converter (V 1 , V 2 ) when the maximum voltage (UC 3 ) is exceeded, the dissipation element (R 8 ) converting electrical energy into thermal energy when a maximum value for the voltage (UC 6 ) across the intermediate circuit capacitor (C 6 ) determined by the dissipation element is exceeded, and the current through the measuring resistor (R 3 ) being measured as the voltage (UR 3 ) across said measuring resistor (R 3 ), being detected in the delay circuit (R 4 , R 5 , C 3 ), and being fed to the shutdown device (SD) as the input signal (UC 3 ).