Patent ID: 8884542

Claim:
An electronic ballast for driving at least one light-emitting device, comprising: a square wave generator receiving a DC input voltage and having a plurality of switch elements for converting the DC input voltage into a square-wave AC voltage according to switching operations of the plurality of switch elements; a transformer having a driving winding and first and second inductive windings mutually connected with each other, wherein the first and second inductive windings are respectively connected to a control terminal of the corresponding one of the plurality of switch elements, the transformer further including a third inductive winding that is magnetically coupled to the first and second inductive windings and to the drive winding; a resonant circuit connected to the driving winding and the at least one light-emitting device for receiving the square-wave voltage through the driving winding and converting the square-wave voltage into an AC output voltage to drive the at least one light-emitting device; and an auxiliary control unit connected to the third inductive winding of the transformer to directly control a voltage waveform of the third inductive winding which, due to the magnetic coupling, indirectly controls a voltage waveform of the first and second inductive windings according to at least one control signal, thereby changing the voltage waveform of the first and second inductive windings for adjusting switching frequencies of the plurality of switch elements.