Harmonic current injection to avoid acoustic resonance in 70W HPS lamps

The present paper deals with the study of the harmonic injection technique, with the objective of avoiding acoustics resonance, in high-pressure sodium lamps (HPS) of 70 W, when supplied by electronic ballast. A prototype of a three level full bridge PWM electronic ballast was developed which allows the injection of harmonics in the voltage supplied to the 70 W HPS lamp. The design procedure and results of the inverter used in ballast are then presented. The dimensioning of the resonant circuit for the lamp ignition, based on the voltage beating technique is made. These techniques allow the control of the current crest factor other than rejecting the AR.