Patent ID: 8222834

Claim:
An electronic ballast for powering a high intensity discharge lamp, the ballast comprising: a voltage step-down circuit arranged to reduce a DC voltage provided by a DC power supply; an inverter circuit coupled to receive said reduced voltage, said inverter circuit including at least one high frequency switching element and arranged to provide a high frequency AC voltage as a function of a driving signal; a resonant circuit coupled to receive the high frequency AC voltage from the inverter circuit, and further operable to couple to the discharge lamp; a voltage step-down control circuit configured to control the DC voltage output from the voltage step-down circuit; a driving circuit configured to supply the driving signal to the at least one switching element of the inverter circuit, and further configured to adjust a driving frequency of the driving signal, thereby controlling the high-frequency voltage; wherein the voltage step-down control circuit controls the DC voltage output from the voltage step-down circuit to a low level such that the high frequency AC voltage in a first operating mode is controlled to a low level wherein the lamp is prevented from starting while the driving circuit sweeps the driving frequency of the driving signal down from a preset initial frequency until the high frequency AC voltage increases to a predetermined voltage, and wherein the voltage step-down control circuit controls the DC voltage output from the voltage step down circuit to a high level such that the high frequency AC voltage in a second operating mode is controlled to a high level wherein the discharge lamp can be started and the driving frequency of the driving signal is prevented from going below the driving frequency at which the high frequency AC voltage increased to the predetermined voltage in the first operating mode.