Novel scheme of ballast for HID lamps using distributed constant line

A novel type of solid state ballast, which operates in the MHz-range frequency, is presented in this paper. A circuit composed of a voltage-fed half-bridge inverter, a distributed constant line, and a parallel LC resonant circuit has been developed for this purpose. 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 λ, the output voltage of the voltage-fed inverter can be converted to a current source on the load side. Therefore, the ballast can supply not only high voltage to the HID lamp for initiating discharge but also constant current to it during discharge condition. The experimental results from a prototype system verify the theoretical procedure