A dimming and protection method for the self-oscillating half-bridge ballast circuit

Conventional voltage-fed self-oscillating half-bridge topology has been widely used in the electronics ballast. The major design challenge in such a ballast circuit is how to dim and protect such a self-oscillating circuit, which usually adds system cost and complexity. In this paper, a novel method is proposed to tackle this problem. The dimming method is achieved by simply controlling the gate drive signal delay time. The protection circuit not only ensures the full-range zero voltage switching operation, but also protects the self-oscillating ballast against possible fault modes operation. In addition, the proposed solution also provides the feature to program lamp start-up processes so that ballast designers can optimize their design so as to maximize lamp life and lumen maintenance. The method can be implemented in ballasts for various gas discharge lamps. Theoretical analysis, circuit simulation and experimental results are given to validate the proposed solution.