In this paper, a new modified valley fill circuit is proposed to combine with a half-bridge current source resonant inverter as the power circuit for a high power factor valley fill electronic ballast. The proposed circuit is capable to lower the discharge voltage of the valley fill capacitance by inserting another branch of valley fill capacitor in the original circuit. When the capacitors are connected in parallel, the voltage discharged across the capacitors is only one-third of the peak line voltage, which allows the conduction angle of the line current to be further extended so that a lower total harmonic distortion level can be achieved. Another advantage is that the smaller capacitance greatly reduces the current spike demanded at the peak line voltage when compared to the one seen in the conventional valley fill ballasts. The high crest factor problem is also eliminated in the proposed circuit as continuous variable frequency control is employed to continuously regulate the lamp current to stay within a steady envelope. Detailed explanations on the operating principles of the proposed circuit are provided in this paper. Simulation and experimental results are provided to validate with all the theoretical analysis for a 20W compact fluorescent lamp.
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