Protected low-pressure discharge lamp operating circuit

Protected low-pressure discharge lamp operating circuit, particularly for connection to at least one discharge lamp (3, 3') having

• connection means (1, 2) for connection to a d-c source;
• an oscillatory circuit including
• a ballast inductance (L1, L1') and a capacitor (C1, C1') connected to the at least one lamp, the ballast inductance and the capacitor being interconnected and forming at least one series resonance circuit (4,4') coupled to the respective at least one lamp,
• and two serially connected transistors (T1, T2) of the same conductivity type, connected across the d-c source, and further coupled to said resonance circuit (4,4') to form an oscillatory circuit therewith;
• and a high-voltage disconnect safety circuit (11) including a controlled switching element (TH) connected to at least one of the transistors (T1) in a circuit to block conduction of said at least one transistor upon conduction of said switching element,
• wherein, in accordance with the invention,
• means are provided to deliver operating energy to said switching element (TH) for rendering said switching element conductive when an excessively high voltage is sensed in said circuit, comprising
• a capaictor (C3);
• and a rectifier (D1, D1') connected to the at least one ballast inductance (L1,L1') in the series resonance circuit at a high-tension terminal thereof to derive power from the inductance and provide rectified electrical energy to charge the capacitor (C3) and store said operating energy therein.