| 摘要 |
<p>A ballast circuit for a gas discharge lamp comprises a resonant load circuit incorporating the gas discharge lamp (18) and including a resonant inductance (LR) and a resonant capacitance (CR). A d.c.-to-a.c. converter circuit induces an a.c. current in the resonant load circuit. The converter circuit comprises first and second converter switches (SnSp) serially connected in the foregoing order between a bus conductor (12) at a d.c. voltage and a reference conductor (14), and being connected together at a common node (16) through which the a.c. load current flows. The first and second converter switches comprise respective interconnected control nodes respective reference nodes interconnected together at a common node. The voltage between each control node and associated reference node determines the conduction state of the associated switch. A voltage-limited energy source (34) is connected between first and second nodes (41,42). The first node (41) is connected to the bus conductor through a first bootstrap capacitor (C1), and the second node (42) is connected to the reference conductor through a second bootstrap capacitor (C2). A bridge network (22) is connected between the first and second nodes and has first and second input nodes (26,30) on which respective first and second input signals are applied. First and second output nodes (24,28) are respectively connected to the common and control nodes (16,29) so as to control the switching state of the converter switches. The first and second pairs of gate control switches (P1, N1; P2, N2) are arranged to cause repetitive cycling through various states the converter switches, so as to allow residual energy from the resonant inductor to cause replenishing of the energy source. <IMAGE></p> |
