Practical stability analysis of frequency controlled dimmable ballasts

Abstract

Electronic ballasts for fluorescent lamps (FL) substitute the electromagnetic ones due to some advantages, such as: (1) no flicker, audible noise or stroboscopic effect; (2) light weight and small size; (3) higher FL light output; (4) reducing of electric power consumption. Moreover, the dimmable electronic ballasts make possible to cut even more the energy consumption and to offer more lighting comfort. The switching frequency dimming until 30% of the rated FL power generally can be implemented under open loop control scheme, while a wider dimming range requires the closed-loop one. The paper presents a practical method for FL – ballast stability analysis and describes a compensator design method. The theoretic analysis is verified experimentally on the dimmable ballast prototype designed to feed one T8 32 W FL. Key words: fluorescent lighting, power electronics, electronic ballast, dimming, stability.