HID lamp ballast with controlled DC step down circuit

摘要

An electronic ballast is provided for powering a high intensity discharge lamp. A voltage step-down circuit is arranged to reduce an input DC voltage. An inverter circuit includes at least one high frequency switching element is and arranged to convert the reduced voltage to a high frequency AC voltage. A resonant circuit receives the high frequency voltage and is further coupled to the discharge lamp. A voltage step-down control circuit controls the DC voltage output from the voltage step-down circuit. A driving circuit supplies a driving signal to the switching element of the inverter, and further adjusts a driving frequency of the driving signal, thereby controlling the high-frequency voltage. The high frequency voltage in a first operating mode is controlled to a low level wherein the lamp is prevented from starting. The high frequency voltage in a second operating mode is controlled to a high level wherein the discharge lamp can be started.