In this paper, a new method is proposed to avoid acoustic-resonance-related instabilities in metal halide lamps when operated with a high-frequency electronic ballast. Angle modulation of the inverter switching pattern has been used as a vehicle to randomize lamp driving frequency and to limit lamp power spectrum below the instability threshold. The optimal modulating pattern is obtained by studying the angle-modulated spectra by periodic and random signals. Analysis is supported by simulations and verified experimentally with the ballasting of 250-W lamps.
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