Patent ID: 7696701

Claim:
A circuit for powering at least one halogen lamp, the circuit comprising: an inverter; and an output circuit coupled between the inverter and the at least one halogen lamp; wherein the inverter and output circuit are operable to provide a magnitude-limited current to the at least one halogen lamp, such that the lamp power during an initial period is substantially less than the lamp power during a steady-state operating period; wherein the inverter comprises: first and second inverter input terminals for receiving a substantially direct current (DC) voltage source; an inverter output terminal, at which the inverter provides a substantially alternating current (AC) output voltage; first and second inverter switches coupled to the inverter input terminals and to the inverter output terminal; and an inverter control circuit coupled to the first and second inverter switches, and operable: (i) during a first period, to commutate the inverter switches at a first frequency; and (ii) during a second period following the first period, to commutate the inverter switches at a second frequency, wherein the second frequency is lower than the first frequency; and wherein the inverter control circuit comprises: an inverter driver circuit coupled to the first and second inverter switches, the inverter driver circuit including a DC supply input, a first frequency control input, and a second frequency control input; a startup circuit coupled between the first and second inverter input terminals and the DC supply input of the inverter driver circuit; a bootstrapping circuit coupled between the output terminal of the inverter and the DC supply input of the inverter driver circuit; and a frequency control circuit coupled to the bootstrapping circuit and to the first and second frequency control inputs of the inverter driver circuit, wherein the frequency control circuit is operable; (i) during the first period, to direct the inverter driver circuit to commutate the inverter switches at the first frequency; and (ii) during the second period, to direct the inverter driver circuit to commutate the inverter switches at the second frequency.