Patent ID: 8253351

Claim:
An electronic ballast comprising: a DC converting circuit operable to convert an AC output from a commercial power source into a DC output; an inverter circuit operable to convert an output from the DC converting circuit to a high frequency output, said inverter circuit having an operating frequency determined by a control signal; a resonant circuit connected to an output end of the inverter circuit, the resonant circuit having a series resonant circuit formed of an inductor and a capacitor and a discharge lamp with the high frequency output supplied thereto from the inverter circuit; processor having three operating modes including a preheating mode for preheating a filament of the discharge lamp, a starting mode for applying a starting voltage to the discharge lamp, and a lighting mode for supplying power to maintain lighting of the discharge lamp, said processor for providing the control signal to control the operating frequency of the inverter circuit according to each operating mode of the processor; a first detection circuit operable to detect a voltage of an output of the inverter circuit; a second detection circuit operable to detect a voltage across the discharge lamp; and a feedback circuit operable to perform feedback control on the control signal so that the detected voltage of the output of the inverter substantially coincides with a predetermined value corresponding to the control signal as provided by the processor, wherein: the processor has an adjustment function to account for variations in components, the adjustment function causes a storage circuit of the ballast to store a set value of the control signal in corresponding to an operating frequency of the inverter circuit for each of the preheating mode, the starting mode and the lighting mode and a target range, and cause the storage circuit to store a corrected set value obtained by correcting the set value so that the detected voltage across the discharge lamp falls within a target range for each operating mode of the processor, and the processor switches paths to supply the control signal corresponding to the set value to the inverter circuit between a path passing through the feedback circuit during normal operation and a path without passing through the feedback circuit during the adjustment function for the preheating mode and starting mode.