BALLAST FOR ELECTRONIC FLUORESCENT LAMP

摘要

PURPOSE: A ballast is provided to lengthen the useful life of lamp by allowing a dimming operation to be performed after elapse of a predetermined time since applying of initial start voltage. CONSTITUTION: A ballast comprises a lamp(L); a bridge rectifying unit(10) for converting an AC voltage into a ripple voltage; a voltage charging unit(30) for charging a voltage; an inverter(60) for performing a high speed switching operation; a resonator(70) for resonating a high speed switching voltage generated by the inverter; a frequency generating unit(80) for generating a high frequency corresponding to each stage of dimming operation; a frequency control unit(110) for changing the frequency generated from the frequency generating unit; a dimming control unit(120) for controlling dimming of the lamp by transmitting a dimming control signal to the frequency generating unit in cases where the charging voltage is lower than a predetermined voltage and transmitting a dimming control signal selected by a level selection switch to the frequency generating unit in cases where the charging voltage is higher than the predetermined voltage; and a lamp detection and initial power supply unit(130) for detecting the existence of the lamp, receiving the initial start voltage from the bridge rectifying unit, and supplying the initial start voltage to the frequency generating unit.