Investigation of a new control strategy for electronic ballasts based on variable inductor

In this paper, a new control method for electronic ballasts based on the use of a variable inductor is presented. The main goal is to perform the complete control of the electronic ballast by maintaining the switching frequency constant and without using other parameters of the power converter, such as input voltage or duty cycle. The magnetic regulator is controlled by means of a dc current, which allows performing both lamp soft starting and lamp dimming. Apart from the important advantage of keeping a constant frequency during full electronic ballast operation, the proposed method presents additional advantages when compared to other control methods, such as inherent isolated control, more linear control characteristics, constant electrode power, and higher efficiency. Experimental results from a 36-W linear fluorescent lamp prototype are presented.