A novel valley fill high power factor electronic ballast with dimming feature and low crest factor. Part II. controller circuit design

In this paper, a novel variable frequency controller is proposed for a passive high power factor electronic ballast with dimming capability and low crest factor. The ballast circuit is the combination of a valley fill circuit and a new frequency modulated current fed resonant inverter. The advantage of using a current fed resonant inverter in the proposed power circuit is that it provides isolation to the driver circuit without the use of any isolation devices. The proposed controller circuit uses a simple modified 555 timer to continuously regulate the lamp current by changing the switching frequency. As a result, a low crest factor in the lamp current is achieved with a high input power factor. A detailed description of the controller circuit is given in this paper. Feedback loop analysis is also provided to study the stability issues of the proposed ballast circuit. Powersim (PSIM) simulation results are presented to highlight the merits of the proposed circuit for a T8-32 W fluorescent lamp