Disclosed is an
inverter circuit for
discharge lamps, in which transformers are separated into plural small or middle-sized transformers connected to one another to provide a high-power
transformer equivalent to a large
transformer. The
inverter circuit includes a plurality of leakage flux step-up transformers each having a magnetically continuous central core, a primary winding, and a distributed-constant secondary winding, wherein a part of a
resonance circuit is formed among a
leakage inductance produced on the secondary winding side, a distributed
capacitance of the secondary winding and a
parasitic capacitance produced around a
discharge lamp close to a proximity conductor, and as the
resonance circuit resonates, the secondary winding has a
close coupling portion in a vicinity of the primary winding which has a
magnetic phase close to that of the primary winding and magnetically close couples with the primary winding and where a large portion of a
magnetic flux produced under the primary winding penetrates, and a
loose coupling portion distant from said primary winding which has a
magnetic phase delayed from that of the primary winding and magnetically loose couples with the primary winding and where a large portion of the
magnetic flux produced under the primary winding leaks, whereby a plurality of
discharge lamps are lighted in parallel. The invention is the only way to achieve the thickness of 10 mm to 13 mm or less which is demanded in the market at present and realize a high-power
transformer of 40 W to 60 W.