Application of multi-mode control strategy in the automotive HID headlight systems

A digitally controlled automotive HID ballast system is presented. The start-up characteristics of HID lamp are analyzed in details. The ballast need to work at different modes at different stages. Different control modes are presented: voltage control mode, current control mode, constant power control mode and variable power control mode. The software flowchart is designed. The key to software design is to identify the important parameters for transitions between stages. Experimental results show that the ballast can achieve all the functions using the multi-mode control strategy.