High Pressure Sodium Lamp High Power Factor Electronic Ballasts Using AC–AC Converters

Electronic ballasts usually present two stages, one for feeding the high pressure sodium (HPS) lamp and the other for power factor correction (PFC). This paper presents electronic ballasts using ac-ac converters without a PFC stage. The use of an indirect ac-ac converter, or an indirect frequency changer, to feed the HPS lamp is investigated. Modulation strategies are proposed to improve the input and output characteristics of the converter. Further studies lead to a novel HPS electronic ballast which uses an ac chopper capable of achieving PFC and supplying high frequency to the lamp. Different converter topologies, bidirectional switches, and a modulation strategy for the ac chopper are presented. Due to the output characteristic of both topologies, the lamp current is modulated at the frequency of the voltage source and the consequences of this operation are discussed. The experimental results for both electronic ballasts supplying 250-W HPS lamps are presented