a current driven toroid - free feedback type ballast comprising a filter and rectifier circuit , a switch and resonant circuit and a lamp load including capacitors , wherein the filter and rectifier circuit is coupled to input ends of the switch and resonant circuit with its output ends ; the switch and resonant circuit is coupled to the lamp load with its output ends and comprising : a trigger circuit comprised of resistors r 1 , r 2 , a capacitor c 3 , a diode d 5 and a trigger diode db 3 ; a half bridge circuit comprised of transistors q 1 , q 2 and resistors ; and a three winding transformer t comprised of primary winding t 3 and two secondary windings t 1 , t 2 . in the current driven toroid - free feedback type ballast of the present invention , the switch and resonant circuit employs a half bridge circuit of transistors together with the transformer to effect driving feedback such that the ballast possess the advantage of toroid - free , which leads to enhanced liability of the lamp load , simplified circuit configuration and manufacturing process whereby to facilitate the miniaturization of electronic ballasts .