Patent ID: 8164280

Claim:
An electronic ballast comprising: a rectifier which rectifies alternating current (AC) power into direct current (DC) power; a power factor compensator which improves a power face of the DC power; an inverter which inverts a DC current into high frequency square wave power, the inverter comprising a first node and a second node as output nodes; and a resonant circuit which receives the high frequency square wave power from the inverter, adjusts impedance, transforms the high frequency square wave power into high frequency sine wave power, and outputs the high frequency sine wave power, the resonant circuit comprising: a first resonant capacitor comprising an end connected to the first node and another end connected to an inductance adjuster; a second resonant capacitor comprising an end connected to the second node and another end connected to the inductance adjuster; and the inductance adjuster having a structure selected from a group consisting of: a first structure comprising: a variable inductor which comprises an end connected to the another end of the first resonant capacitor; and a switch which comprises an end selectively connected to one of a node and another end of the variable inductor and another end connected to the other end of the second resonant capacitor; a second structure comprising: a first resonant inductor which comprises an end connected to the other end of the first resonant capacitor; a second resonant inductor which comprises an end connected to another end of the first resonant capacitor; and a switch which comprises an end selectively connected to one of the other end of the first resonant inductor and another end of the second resonant inductor and another end connected to the other end of the second resonant capacitor; and a third structure comprising: first through n th resonant inductors comprising ends respectively connected to the other end of the first resonant capacitor in parallel; and a switch comprising ends selectively connected to other ends of the first through n th resonant inductors and another end connected to the other end of the second resonant capacitor.