Gas discharge lamp ballast with tapless feedback circuit

A ballast circuit for a gas discharge lamp with a tapless feedback circuit, comprising:

• a) d.c.-to-a.c. converter circuit with means for coupling to a resonant load circuit, for inducing a.c. current therein, said converter circuit comprising:
• i) a pair of switches serially connected between a bus conductor at a d.c. voltage and a reference conductor, the voltage between a reference node and a control node of each switch determining the conduction state of the associated switch;
• ii) the respective reference nodes of said switches being connected together at a common node through which said a.c. current flows, and the respective control nodes of said switches being connected together;
• b) a gate drive arrangement for regeneratively controlling said first and second switches, said arrangement comprising:
• i) a coupling circuit including an inductor for coupling to said control nodes a feedback signal representing current in said load circuit;
• ii) a tapless feedback circuit for providing said feedback signal;
• said feedback circuit comprising a capacitor coupled at one end to said common node in such manner as to conduct load current, and coupled at another end to said inductor;
• and
• iii) a bidirectional voltage clamp connected between said common node and said control nodes;
• iv) said inductor cooperating with said voltage clamp is such manner that the phase angle between the fundamental frequency component of voltage across said load circuit and said a.c. load current approaches zero during lamp ignition.