A high-power-density electronic ballast for low-power HID lamps

A two-stage structure comprised of a regulated single-stage power factor correction (S²PFC) AC/DC front end and an unregulated low-frequency DC/AC inverter is selected as a high-power-density solution for the low-power high-intensity-discharge (HID) lamp ballast. An S²PFC AC/DC converter is proposed as the front end in order to achieve a unity power factor, low total harmonic distortion (THD), low bulk capacitor voltage, and constant output power control. A prototype is developed with an input power factor of 0.996 and an input-current THD of 8.077% at nominal (120 Vac) input. The total efficiency at 120 Vac is 84.2%. The power density of the entire ballast is about 4.68 W/inch³, which is twice the density of commercial products.