DIGITAL CONTROLLED ELECTRONIC BALLAST WITH PIEZOELECTRIC TRANSFORMER

摘要

A digital controlled electronic ballast with a piezoelectric transformer which is capable of supplying high power of the 28-Watt class to the ballast, whereby the ballast automatically controls precisely the brightness of a lamp in a digital frequency modulation manner and applies stable voltage and current to the lamp. The ballast comprises a rectifier for rectifying an input low-frequency AC voltage to convert it into a DC voltage, a power factor improvement circuit for compensating a power factor for a variation in the input low-frequency AC voltage to maintain the level of an output DC voltage from the rectifier constant, an inverter for performing a switching operation for an output DC voltage from the power factor improvement circuit to convert it into a high-frequency AC voltage, a resonance circuit for transferring the high-frequency AC voltage from the inverter to the lamp, the resonance circuit including a coil and a high-power piezoelectric transformer, and a digital controller for modulating a frequency controlling a switching period of the inverter when the lamp is turned on/off, to control an intensity of illumination of the lamp. The piezoelectric transformer is made of a composition of 1 ${\mathrm{Pb}}_{1-a}it{\mathrm{Sr}}_a\left[{\left({\mathrm{Ni}}_{\frac{1}{2}}it{W}_{\frac{1}{2}}\right)}_{b}it{\left({\mathrm{Mn}}_{\frac{1}{3}}it{\mathrm{Nb}}_{\frac{2}{3}}\right)}_{c}it{\left({\mathrm{Zr}}_{1-x}it{\mathrm{Ti}}_x\right)}_{1-b-c}\right]it{O}_3+\mathrm{kPbO}.$ .