Patent ID: 6509699
Filing Date: 2003-01-21
Classification: H05B

Abstract:
A digitally controlled electronic ballast for turning on/off a lamp, said ballast comprising:a rectifier for rectifying an input low-frequency alternating current (AC) voltage to obtain a direct current (DC) voltage; a power factor improving circuit coupled to said rectifier for maintaining the DC voltage outputted from said rectifier at a constant level; an inverter coupled to said power factor improving circuit for performing a switching operation to convert a power factor-improved DC voltage received from said power factor improving circuit into a high-frequency AC voltage; a resonance circuit connected to an output of said inverter for supplying said high-frequency AC voltage from said inverter to the lamp, said resonance circuit including a coil and a high-power piezoelectric transformer coupled to said coil, said piezoelectric transformer including a substantially hexahedral piezoelectric body having opposite upper and lower surfaces, a substantially rhombic input electrode formed in a central portion of each of said upper and lower surfaces of said piezoelectric body, and an output electrode formed on each of said upper and lower surfaces of said piezoelectric body, said output electrode surrounding the respective input electrode while being spaced from said input electrode at a regular interval; and a digital controller coupled to at least said inverter for modulating a switching frequency controlling a switching period of said inverter, when the lamp is turned on/off, to control an intensity of illumination of the lamp.