Lighting circuit for an electric discharge lamp

摘要

A lighting circuit 1 for an electric discharge lamp. The circuit includes a DC electric power source circuit 3, DC-AC conversion circuit 4 and starting circuit 5. The starting circuit 5 includes a primary circuit of a transformer has a condenser and switch element, and the switch element is closed so that a high voltage signal for starting is impressed upon an electric discharge lamp from a primary winding via a secondary winding when voltage across both terminals of a condenser exceeds a threshold value in accordance with an accumulation of electric charges in the condenser. In the case where an output voltage of the DC electric power source circuit 3 is positive (or negative) with respect to the electric potential of ground, the polarity of supply voltage supplied from the DC electric power source circuit 3 or the DC-AC conversion circuit 4 for charging the condenser in the starting circuit 5 (the primary circuit in the starting circuit 5) is regulated to be negative (or positive).