Steady-state analysis and simulation of a BJT self-oscillating ZVS-CV ballast driven by a saturable transformer

The steady-state oscillation of a zero-voltage-switching clamped-voltage self-oscillating ballast driven by a saturable transformer is analyzed and simulated. Its self-oscillating operation is divided into six stages according to the hysteresis B-H loop of saturable transformer cores. Stage-wise circuit analysis shows the saturable transformer limits the lamp current and dominates the switching frequency of the ballast. The saturating behavior of driving and switching devices clearly distinguishes this self-oscillating inverter from an external-drive high-quality-factor resonant inverter. Analytical results are verified by mathematical simulation and laboratory experiment.