Implementation of A DSP-Based Controller for Electronic Ballast for Automotive Xenon Lamps

Xenon lamp is nowadays the most popular type of automotive headlights. The High intensity discharge (HID) lamps have been used in headlights system with high efficiency, long life and natural color. There has been an emerging demand to replace the conventional halogen headlamps with the newly introduced small-wattage metal halide HID Lamps.
In general, the lamp ballast for automotive headlamp consists of four parts: DC/DC converter, Ignition circuit, DC/AC Inverter circuit, Control circuit. Because of the HID lamp has negative incremental impedance, one of the major issue of ballast design is the ballast system stability. Beside, Due to the complex lamp V-I profile and timing control requirement, control circuit built with conventional analog control is unavoidably cumbersome. With the flexibility and programmability, digital controller shows more advantages in this application.
An automotive HID ballast with DSP (digital signal processor) is developed. The small signal model of ballast/HID lamp is also presented and used to analyze the stability of the system.