Patent ID: 7166971

Claim:
Circuit arrangement for operating a high pressure discharge lamp comprising input terminals for connection to a supply voltage source, a DC-DC-converter coupled to the input terminals for generating a DC current out of a supply voltage supplied by the supply voltage source and comprising a control circuit for controlling the DC current at a value that is represented by a reference signal Sref, a reference circuit for generating the reference signal Sref, and an output capacitor, a commutator for commutating the polarity of the DC current and comprising lamp connection terminals and an ignition inductor, a first circuit part for modulating the reference signal Sref at a modulation frequency that equals the frequency of the commutation of the DC current by subsequently decreasing the reference signal Sref by an amount ΔSref during a first time interval Δt 1 that starts a second time interval Δt 2 before each commutation of the DC current, maintaining the reference signal at the decreased value during a third time interval Δt 3 , increasing the reference signal Sref by an amount ΔSref during a fourth time interval Δt 4 , characterized in that the circuit arrangement further comprises a second circuit part for adjusting at least one parameter chosen from the group formed by ΔSref, Δt 1 , Δt 2 , Δt 3 and Δt 4 in dependency of a parameter chosen from the group formed by the power consumed by the lamp, the lamp voltage and the lamp current.