An input dc-voltage, usually obtained from an AC-mains voltage through a pre-connected rectifier and Power Factor Corrector, is converted by a series connection of two power transistors to an ac-voltage, which, via an LC section is presented to a gas discharge lamp.For starting the lamp, the power transistors are switched with a frequency which is slightly higher than approximately one-third or one-fifth of the resonance frequency of the LC section.Circuits have been provided for limiting the output voltage, for limiting the lamp current and for stabilizing the lamp output. Safety circuits switch the power circuit off if the lamp does not ignite or if the lamp exhibits rectifying effect.