Patent ID: 7605544

Claim:
A current balancing circuit for a discharge lamp unit, the discharge lamp unit including a first lamp set and a second lamp set, the first lamp set including first, second, third and fourth discharge lamps, the second lamp set including at least one discharge lamp, said current balancing circuit comprising: a step-up transformer adapted to be coupled electrically to a power supply for receiving an alternating-current source power therefrom, and for generating a drive signal by varying magnitude of the alternating-current source power, said step-up transformer being further adapted to be coupled electrically to the first and second lamp sets of the discharge lamp unit for providing the drive signal thereto; and a current balancer including first and second shunt transformers, each of said first and second shunt transformers including primary and secondary windings that correspond to each other in number of turns thereof, one end of each of said primary and secondary windings of said first shunt transformer being adapted to be coupled electrically to a corresponding one of the first and second discharge lamps of the first lamp set, the other end of said primary winding of said first shunt transformer being coupled electrically in series to the other end of said secondary winding of said first shunt transformer, one end of each of said primary and secondary windings of said second shunt transformer being adapted to be coupled electrically to a corresponding one of the third and fourth discharge lamps of the first lamp set, the other end of said primary winding of said second shunt transformer being coupled electrically in series to the other end of said secondary winding of said second shunt transformer and to said other ends of said primary and secondary windings of said first shunt transformer, said current balancer being further adapted to mirror current flowing through said first and second shunt transformers to the second lamp set.