Inductor phase feedback for phase-locked loop control of electronic ballasts

This paper proposes a novel phase-locked loop (PLL) control technique for electronic ballasts, using the phase-feedback signal from the resonant inductor. Generally speaking, the electronic ballast with PLL control has been used to drive some high-voltage lamps with high equivalent resistance at the steady state, such as cold-cathode fluorescent lamps (CCFLs). With the proposed control scheme for electronic ballasts is thus developed to tolerate lower equivalent resistance of the lamps at the steady state, to have the operating frequency of ballasts continuously track the resonant frequency of the resonant tank. Based on the derived analysis of the proposed PLL control scheme, the design and the implementation of a prototype circuit is provided to demonstrate the performance of the proposed PLL scheme associating with a current regulator circuit.