Patent ID: 7528558

Claim:
A ballast for powering at least one gas discharge lamp, the ballast comprising: an inverter having an inverter output terminal and being operable to provide, at the inverter output terminal, an inverter output voltage having an operating frequency; a resonant output circuit coupled between the inverter output terminal and the lamp, and operable to provide an ignition voltage for igniting the lamp; a control circuit coupled to the output circuit and the inverter, wherein the control circuit is operable: (a) to monitor a voltage within the resonant output circuit; (b) in response to the monitored voltage reaching a specified level, to control the inverter to maintain its operating frequency at a present value for a predetermined period of time so as to allow the resonant output circuit to maintain, for the predetermined period of time, the ignition voltage at a suitable level for igniting the lamp; (c) in response to ignition of the lamp within the predetermined period of time: (i) to cease controlling the inverter to maintain its operating frequency at the present value, and (ii) during a lamp stabilization period, to prevent the operating frequency from falling below a specified minimum value; and (d) in response to failure of the lamp to ignite within the predetermined period of time, to deactivate the inverter.