Patent ID: 7446641

Claim:
A balance transformer disposed in a circuit for driving a plurality of discharge lamps, comprising: a first transformer portion having a first primary winding and a first secondary winding; a second transformer portion having a second primary winding and a second secondary winding; and a magnetic core composed of a loop-shaped outer frame portion and a short portion to short inside of said outer frame portion, wherein a first small loop path composed of a part of said outer frame portion and said short portion is disposed with only two windings of said first transformer portion from among all windings, and a second small loop path composed of another part of said outer frame portion and said short portion is disposed with only two windings of said second transformer portion from among all windings, and wherein a first magnetic flux generated at said first transformer portion circulates along said first small loop path, and a second magnetic flux generated at said second transformer portion circulates along said second small loop path in a direction reverse to said first magnetic flux.