Patent ID: 7288897

Claim:
A circuit arrangement for operating at least one high-pressure discharge lamp ( 16 ) having: four switches (Q 1 to Q 4 ) in a full bridge arrangement, a first and a second switch (Q 1 , Q 2 ) forming the first half-bridge arm, and a third and a fourth switch (Q 3 , Q 4 ) forming the second half-bridge arm, at least two terminals for coupling the high pressure discharge lamp between the midpoint (M 1 , M 2 ) of the first and of the second half-bridge arms, at least one terminal for supplying the circuit arrangement with a DC voltage signal (U v ); and a drive circuit for driving the four switches, the drive circuit being designed to provide a first drive signal (Ā) for the switches (Q 1 , Q 2 ) of the first half-bridge arm and a second drive signal (B) for the switches (Q 3 , Q 4 ) of the second half-bridge arm in such a way that the first and the second drive signals (Ā, B) are derived from a base signal (A) whose clock pulse is swept between a first and a second frequency, and in such a way that the first and the second drive signals (Ā, B) have a phase difference which is modulated with a prescribeable third frequency (f AM ), characterized in that in order to modulate the phase difference the drive circuit comprises at least one switch ( 24 ) which is designed in such a way as to switch to and fro between derivatives of the base signal with a different phase shift in time with the third frequency (f AM ).