Solid-state fluorescent lamp ballast

Claim 1

A solid-state dimmable fluorescent lamp ballast circuit comprising: rectification means for supplying a unipolar electrical voltage; a first switch adapted to couple a first side of the output of said rectification means to one side of a gaseous discharge lamp; a second switch adapted to couple said first side of the output of said rectification means to the other side of a gaseous discharge lamp; a third switch adapted to couple a second side of the output of said rectification means to said one side of a gaseous discharge lamp; a fourth switch adapted to couple said second side of the output of the said rectification means to said other side of a gaseous discharge lamp; control means for providing first and second complementary pulse trains and third and fourth variable duty cycle pulse trains, said first pulse train being coupled to said first switch, said second pulse train being coupled to said second switch, said third pulse train being coupled to said third switch and said fourth pulse train being coupled to said fourth switch wherein said fourth switch is closed for a variable percentage of the time said first switch is closed and said third switch is closed for a variable percentage of the time said second switch is closed, said control means comprising: oscillator means for providing an output having a first frequency; multiple stage divider means coupled to said oscillator means for providing an output at a second frequency; first means coupled to the output of said multiple stage divider for providing said first and second pulse trains; second means selectively coupled to at least one intermediate stage of said multiple stage divider for providing said third and fourth pulse trains; and means for varying the duty cycle of third and fourth pulse trains.