High frequency electronic ballast for HID lamps based on λ/4-long distributed constant line with buck-boost AC-DC converter suitable for half bridge inverter

A novel type of solid state ballast, which operates in the MHz-range frequency, is presented in this paper. A circuit composed of a buck-boost type AC-DC converter (rectifier), a voltage-source half-bridge inverter, a distributed constant line, and a parallel LC resonant circuit has been developed for use in this new ballast. The HID (High Intensity Discharge) lamp is connected to the output terminal of the inverter through the distributed constant line. Here, since the length of the line is adjusted to 1/4 of the propagation wavelength lambda (lambda/4 condition), the output voltage of the voltage-source inverter can be converted to a current source at the load side. Therefore, the ballast can supply the HID lamp not only with high voltage to initiate discharge but also with stable current during lamp running conditions. Further, the proposed ballast enables the BID lamps to control luminous intensity and to re-ignite automatically with the novel buck-boost AC-DC converter and the discharge current feedback control. The experimental results from a prototype system verify the theory underlying this research.