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 watt lamps.
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