Lamp power supply circuit with electronic feedback circuit for switch control

A ballast circuit for a gas discharge lamp, comprising:

• (a) a resonant load circuit including a gas discharge lamp and first and second resonant impedances whose values determine the operating frequency of said resonant load circuit;
• (b) a d.c.-to-a.c. converter circuit coupled to said resonant load circuit so as to induce an a.c. current in said resonant load circuit, and comprising first and second power switches serially connected between a bus conductor at a d.c. bus voltage and ground, and having a common node through which the a.c. load current flows;
• and
• (c) a feedback arrangement for regeneratively controlling said first and second switches;
• said arrangement including a circuit for sensing a.c. current in said resonant load circuit and producing a feedback signal in proportion to said a.c. current;
• said feedback arrangement further including:
• (i) a comparator circuit for comparing said feedback signal with a periodic reference signal, and for producing a comparator output signal that changes state when a first one of the compared signals becomes greater than the second of the compared signals, and that further changes state when the second of the compared signals then becomes greater than the first of the compared signals;
• (ii) a circuit for generating said periodic reference signal including means, responsive to said comparator output signal, for causing transitions from a predominantly higher-going portion to a predominantly lower-going portion of said periodic reference signal, and vice-versa;
• and
• (iii) a conditioning circuit receptive of said comparator output signal for controlling said first and second switches.