Circuit arrangement

A circuit arrangement for feeding a discharge lamp, comprising

• lamp contacts for making electrical contact with the discharge lamp,
• a main inverter coupled to the lamp contacts for generating, during operation, a current which is fed to the discharge lamp,
• an auxiliary inverter for preheating electrodes of the discharge lamp, including:
• an oscillator for generating an alternating voltage with a frequency f1,
• a transformer including a primary winding coupled to the oscillator, and a first and a second secondary winding which each shunt a lamp electrode during operation of the lamp,
• a control circuit coupled to the main inverter and the auxiliary inverter for controlling the operating state of the circuit arrangement,
• a first circuit part coupled to an input of the control circuit for generating a first signal which represents the voltage difference between a first end of the first secondary winding and a first end of the second secondary winding, characterized in that a second end of the first secondary winding and a second end of the second secondary winding are interconnected by a first conducting branch, and in that, during operation of the circuit arrangement, the polarity of the voltage across the first secondary winding is equal to the polarity of the voltage across the second secondary winding, whereby said first signal indicates whether the lamp is electrically connected to said lamp contacts.