High-Power-Density Electronic Ballast for Low Wattage HID lamps
High Intensity Discharge (HID) lamps are noted for high efficacy (lumen/watt), long life, good color rendition and compact volume, in contrast to fluorescent lamps and incandescent lamps. To achieve stringent PFC requirement and avoid acoustic resonance, HID ballast usually has complicated and expensive three-stage structure, including PFC, DC/DC power regulation and DC/AC inverter. Therefore, how to reduce the component count and improve the power density is a big challenge for the designer of the electronic ballast.
A compact electronic ballast circuit for low wattage HID lamps was proposed, which has a two-stage structure: a regulated single-stage PFC AC/DC front-end can accomplish both power factor correction function and a constant output power, and a unregulated low frequency DC/AC inverter is used to provide an ignition voltage and change the DC current/voltage to a low frequency ac square wave. This structure is potentially a low cost solution and has a simple control circuit, so it is particularly suitable for low power ballast. Topologically, a novel single stage PFC AC/DC converter is proposed as the front-end to achieve a unity power factor, low THD, low bulk capacitor voltage, as well as the constant output power control. The power density of the proposed ballast is more than doubled, and the proposed topology has been commercialized.