Implementation of a voltage multiplier integrated HID ballast circuit with dimming control for automotive application

High-intensity discharge (HID) lamps are becoming popular substitutes for halogen lamps in automotive headlamps because of the high lumen/watt ratio and the color of the light. In this paper, a ballast (integrated with a voltage multiplier circuit in the secondary winding of the dc converter transformer) with dimming control is presented. The proposed circuit not only eliminates one auxiliary winding but also reduces the voltage across the switch on the primary side and consequently permits the selection of switches with a lower rating. A brief review of the HID circuits is done and compared with the proposed circuit. Experimental results from the prototype are presented. This paper also presents different methods of dimming the automotive HID lamps based on analog and digital control and discusses the relative merits of each of the methods. The dimming control is implemented using both the methods, and experimental results are presented. It is envisaged that the dimming control will provide some flexibility to drivers in the control of HID lamps to suit the driving conditions in the modern cities that are very well lit at night. This paper investigates the merits of each method and discusses the practical issues for implementing such controls.