Abstract: A gas discharge lamp driver circuit, comprising an inverter (10) of a bridge type, which has first and second input terminals connected to DC power lines (6, 8) for receiving a DC power voltage and output terminals (18) for providing a substantial rectangular power voltage, a ballast (20), which is connected to the output terminals of the inverter and to one or more lamp circuits (30), each having a gas discharge lamp (32) connected in series with a current control circuit having a high frequency semiconductor switch element (34), which receives an individual selection signal (S1, S2) from a selection circuit (36), such that an individual lamp (32) can be selected to operate. If deselected, the switch element conducts such that current is diverted to a selected switch element to thereby only ignite and operate a lamp connected to a selected switch element.

Abstract: In an up-converter supplied by the mains supply and operating in the critical mode, the on-time of the switching element (2) is modulated so that it is increased in the vicinity of the zero crossings of the mains supply voltage. As a result the THD is lowered.

Abstract: In an up-converter a switching element is controlled both by an integrated control circuit and by a secondary winding on an inductor. High power factor and low total harmonic distortion are achieved while the design of the integrated control circuit is comparatively simple.