2.65 MHz self-oscillating electronic ballast with constant lamp-current control for metal halide lamp

摘要

This paper presents the 2.65 MHz self-oscillating electronic ballast with constant-lamp-current control for metal halide lamp. To avoid the inherent acoustic-resonance problem of metal halide lamps, the switching frequency is chosen to be above 1 MHz. Furthermore, in order to satisfy higher magnitudes of maximum EMI limitation at frequencies in between 2.5 MHz to 3.0 MHz, the ballast's switching-frequency level was selected to be 2.65 MHz, which falls within the frequency range “chimney,” for RF lighting systems, such as electrodeless fluorescent lamps. The conventional self-oscillating electronic ballast is disadvantageous because the lamp-current varies according to the input voltage. This difference in lamp-current causes poor quality of illumination for the lamp. In order to solve this issue for the self-oscillating electronic ballast, the constant-lamp-current control circuit is proposed to provide constant lamp-current. Finally, a 20 W self-oscillating ballast with the proposed constant lamp-current control for metal halide lamp is implemented in order to demonstrate the ability to avoid the acoustic-resonance and to provide constant levels of lamp current.