Patent ID: 8502475

Claim:
A discharge lamp ballast comprising: a DC-AC power converter having a plurality of switching elements; a startup circuit coupled between output terminals of the power converter, the startup circuit configured to generate a high voltage to ignite a discharge lamp; a lamp current sensor functional to detect an amplitude of a lamp output current; and a control circuit effective to control the switching elements of the power converter in accordance with each of a plurality of control operations, the control operations comprising a startup operation to ignite a discharge lamp using the high voltage generated by the startup circuit, an electrode heating operation after the startup operation during which the amplitude of the lamp output current detected by the lamp current sensor is compared by the control circuit to a predetermined target current amplitude, further wherein an operating frequency of the switching elements is controlled in a feedback manner during the electrode heating operation so as to set the amplitude of the lamp output current detected by the lamp current sensor to the predetermined target current amplitude, and a normal operation after the electrode heating operation wherein the operating frequency is reduced to maintain stable lamp lighting.