This paper presents the 2.65-MHz self-oscillating electronic ballast with constant-lamp-current control for metal halide (MH) lamps. To avoid the inherent acoustic-resonance problem of MH lamps, the switching frequency is chosen to be above 1 MHz. Furthermore, in order to satisfy higher magnitudes of maximum electromagnetic interference limitation at frequencies of between 2.5 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 radio-frequency lighting systems, such as electrode-less 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 color rendering index 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 MH lamps is implemented in order to demonstrate the ability to avoid acoustic resonance and to provide constant levels of lamp current.
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