Microcontroller power mode stabilized power factor correction stage for high intensity discharge lamp electronic ballast

This paper presents new design considerations and a control strategy for a two-stage ballast system; power factor correction (PFC) and resonant inverter (RI), for high intensity discharge lamps. The ballast includes a microcontroller whose proposed, algorithm implements a power loop and a voltage loop, both to control the PFC, and generates the transistor drive signals of the RI. The power loop adjusts the lamp power in steady state and the voltage loop controls the PFC during the ignition and warm-up time. System stability is studied to verify that the PFC stage provides the ballast with the required stability in long and medium term, while the short term stability is assured by the high output impedance of the LCC inverter, operating in open loop at constant switching frequency. The resulting performance of the ballast shows improvements in ignition repeatability, warm-up time reduction, robustness of the resonant inverter operation, and simple and accurate power control, including dimming operation.