Backlight unit and transformer using the same

A backlight unit includes a light source and a transformer; wherein, the transformer is provided with a primary side and a secondary side; and the primary side is used for receiving a pulse width modulating signal. The invention is characterized in that the secondary side is provided with a first end, a measuring end and a second end; wherein, the first end is earthed and a first inductance value is arranged between the measuring end and the first end; a second inductance value is arranged between the second end and the first end. Besides, the measuring end outputs a measuring voltage used for representing the working characteristic parameters of the light source and the second end outputs a drive signal so as to drive the light source to illume. As the transformer of the invention is provided with the measuring end, the invention can measure various measuring voltages; consequently, a user can acquire various working characteristic parameters of the light source by using the measuring voltages under a situat