A ballast circuit for a gas discharge lamp with a tapless feedback circuit is disclosed. The ballast circuit comprises a d.c.-to-a.c. converter circuit with circuitry for coupling to a resonant load circuit, for inducing a.c. current therein. The converter circuit comprises 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 determines the conduction state of the associated switch. The respective reference nodes of the switches are connected together at a common node through which the a.c. current flows, and the respective control nodes of the switches are connected together. A gate drive arrangement regeneratively controls the first and second switches. It comprises a coupling circuit including an inductor for coupling to the control nodes a feedback signal representing current in the load circuit. It further comprises a tapless feedback circuit for providing the feedback signal. The feedback circuit comprises a capacitor coupled at one end to the common node in such manner as to conduct load current, and coupled at another end to the inductor.