Evaluation of high-frequency sinusoidal waveform superposed with 3rd harmonic for stable operation of metal halide lamps

In this paper a novel topology to supply MH lamps using sinusoidal waveform with superposed third harmonic is proposed. By employing this technique, the lamp is supplied with an approximated square waveform, but reducing the harmonic content and therefore EMI and RFI. The proposed topology is analyzed and designed for a 35 W MH lamp with ceramic discharge tube. Experimental results prove that lamp operation is stable at operating frequencies where acoustic resonances were previously observed when supplied with pure sinusoidal waveforms. As a conclusion, the proposed technique could be a feasible solution for stable operation of MH lamps.