Self-oscillating electronic ballast analysis using the relay systems approach

In this paper, the authors analyze the self-oscillating LC parallel resonant inverter for electronic ballast applications from a control system point of view. It is observed that the self-oscillating parallel resonant inverter with lamp loads can be naturally modeled as a relay system with negative hysteresis. Based on this formulation, the self-oscillating frequencies of the circuit are found via the time-domain-based Hamel locus. Also, the predicted self-oscillating frequencies via the describing function approach and the Hamel locus approach are compared with the prototype measurement results. It turns out that the accuracy of the frequency prediction via the Hamel locus approach is high, while the accuracy via the describing function approach is circuit Q-value dependent.