ELECTRONIC BALLAST HAVING A DIMMING-CONTROLLING PART OF WHICH THE LAMP CURRENT IS MAINTAINED UNIFORMLY BY FEEDBACK-CONTROLLING WITH THE DETECTED CURRENT

摘要

An electronic ballast having a dimming-controlling function to maintain a constant current by comparison of a detected current is provided to maintain constant intensity of illumination regardless of variation of temperature of a lamp or surrounding temperature or operation stop of the ballast, by providing an initial dimming control circuit helping lamp discharge in case of ON/OFF of an input voltage. An electronic ballast has a voltage input part(1), a bridge rectification part(2) rectifying a voltage of the voltage input part, an inverter part(5) driving a lamp(14) by inverting a rectified voltage into a high frequency signal, a frequency oscillation part(4) applying an oscillation frequency to the inverter part and a resonant part(8) forming a resonant circuit with the lamp. A current sensing part(7) senses a current of the inverter part or the lamp. A current comparison part(9) outputs an output value of comparing a voltage of an input terminal with a reference voltage of another input terminal, as a dimming controlling signal. A frequency control part(6) controls the oscillation frequency of the frequency oscillation part according to the dimming controlling signal.