Abstract
A new single-stage dimmable electronic ballast with unity power factor is introduced in this paper. The proposed circuit which is the integration of a buck-boost converter and a half-bridge series resonant parallel loaded inverter is developed by substituting the synchronous switch for the active switches in the two-stage converter. With the plasma model for the lamp, the analysis of the power stage is carried out, from which the control curves are derived. In this dimmable ballast, the combination of pulse-width modulation (PWM) and variable-frequency method is chosen as the control strategy. The proposed single-stage dimmable ballast with the control strategy can save a controller, reduce size and increase system reliability over conventional two-stage systems. Analysis and design of the proposed system are presented. Simulated and experimental results of the ballast for an OSRAM T8 32 W fluorescent lamp are used to verify the theoretical prediction.