Patent ID: 7589478

Claim:
An inverter circuit for discharge lamps for a multi-lamp surface light source, said inverter circuit comprising: at least two coils connected to a secondary winding of a step-up transformer of the inverter circuit without having a capacitor connected in series between the at least two coils and the secondary winding, the at least two coils being connected and magnetically coupled to each other and arranged to form a shunt transformer for shunting current such that opposing magnetic fluxes are generated by the at least two coils which cancel each other out; and at least two discharge lamps connected to said at least two coils, respectively, with currents flowing through said at least two discharge lamps balanced with each other, wherein the at least two discharge lamps are arranged as backlights in a surface light source in which an electrically conductive reflector is arranged in close proximity to said at least two discharge lamps, such that parasitic capacitances are generated between said discharge lamps and said adjacent conductor, said parasitic capacitances being generated in response to said backlights being added to each other as appropriate via said shunt transformer, wherein: the at least two discharge lamps each comprise an electrode portion and a positive column, an impedance characteristic of the electrode portion and the positive column of each of said at least two discharge lamps has a negative resistance characteristic, the respective self inductances of the at least two coils and the coupling coefficient between the at least two coils are set to values producing an inductance for the shunt transformer with a reactance exceeding the negative resistance of each of said at least two discharge lamps while the balanced currents flow through the at least two discharge lamps thereby causing each of said at least two discharge lamps to be lit, said reactance being in an operating frequency of the inverter circuit, a shunt circuit is formed by arranging a plurality of shunt transformers such that said shunt transformers are connected to each other in the form of a tournament tree, whereby shunt transformers are sequentially connected to each other to form a multi-tier structure, windings of coils of each shunt transformer in the multi-tier structure are wound such that magnetic fluxes generated by said respective windings are opposed to each other, and for each tier in the multi-tier structure, one end of each of said two or more coils are connected to each other, with each of the other ends of said two or more coils being connected to the connected ends of two or more coils of a shunt transformer in a subsequent tier, except for the last tier in the multi-tier structure in which the other ends of said two or more coils are connected to respective discharge lamps.