Inductor voltage phase feedback based phase-locked loop control for electronic ballast with series parallel resonant tank

This paper presents a PLL control based electronic ballast with a series parallel resonant tank (SPRT) by sensing the phase signals of the resonant inductor voltage and input voltage in the employed resonant tank in order to have the operating frequency continuously track the resonant frequency of the SPRT independent of load equivalent-resistance in the steady state. In correspondence to the current feedback signal, the tracked resonant frequency is used as a reference frequency for the proposed PLL control scheme to adjust the lamp current or the lamp power by offsetting the operating frequency. The analysis and design of the employed SPRT will be provided for the implementation of the prototype circuit in order to validate the performance of the proposed electronic ballast for a linear fluorescent lamp.