Frequency Diagnostic Universal Fault Protection for Current Fed Parallel Electronic Resonant Ballast

Current fed parallel resonant electronic ballasts (PREB) dominate the applications for the T8 fluorescent lamp in North America for the advantage of low cost, flexibility and high reliability. At fault condition, PREB generates much heat externally, but it is difficult to provide fault protection using traditional approaches without sacrificing other advantages of PREB. In this paper, a digital solution is presented to detect universal fault condition in PREB and preserve its other advantages. Analysis of the operational principal shows that the load impedance disturbance in PREB leads to operation frequency perturbation, which can be detected with a very simple and low cost digital device for fault protections. Experiments show that this frequency diagnostic provides very sensitive and reliable fault detection for PREB. With both end-of-life and anti-arcing protections solved with one algorithm, this technology provides a superior fault protection to one of the most widely used ballast topologies and greatly extends the potential applications of PREB in modern lighting industry