Full digital dimming regulation of fluorescent lamps with -54 dB/Hz light ripple

The digital regulation principle for electronic ballasts for flourescent lamps presented here is well suited for system-on-chip integration of digital controlled ballasts for dimming applications. The digital regulation achieves a 16-bit adjustment accuracy of the lamp voltage frequency from 40 kHz to 120 kHz using only a 40 MHz system clock. A digital second order /spl Delta//spl Sigma/-modulator converts the 16-bit target value for the lamp frequency to a 10-bit value for the digital controlled oscillator that has a time resolution of 25 nsec. The virtual enhancement of the time resolution of the DCO allows a fine adjustment of the average lamp frequency making an analog VCO unnecessary. The principle is well suited for dimming of compact fluorescent lamps down to 1% dim level with a very low light flicker of -54 dB equivalent to 56 /spl mu/W/Hz in the visible frequency range.