Leistungssteuerung eines Vorschaltgerätes für eine Entladungslampe

The invention relates to a circuit arrangement for operating a discharge lamp, comprising a DC-AC converter provided with a branch A having ends suitable for being connected to a DC voltage source and comprising a series circuit of two switching elements for generating a periodic voltage by being conducting and non-conducting alternately with a frequency f, each switching element being shunted by a diode, a control circuit coupled to control electrodes of the switching elements for rendering the switching elements conducting and non-conducting alternately with the frequency f, a load branch B which shunts one of the switching elements and which comprises inductive means L and means for coupling the discharge lamp to the load branch B, means M for adjusting the power consumed by the discharge lamp. According to the invention, the means M comprise means Mp for adjusting the value of the difference Tt-Td, in which Tt is a time interval during which one of the switching elements is conducting during a half cycle of the periodic voltage, and Td is a time interval during which a diode is conducting during this same half cycle of the periodic voltage. It is achieved by this that the discharge lamp burns in a stable manner over a wide range of the adjustable power.