App note: Digital HID Ballast Reference Design

High intensity discharge ballasts, used in cars today, require a large set of analog controllers to ignite an HID bulb and reach steady-state operation. This reference design from Microchip describes how to make an HID ballast using a dsPIC and a few discrete components.

The reference design uses 9-16VDC and outputs 35W of steady state power and reaches an efficiency of over 85%. To handle changes in the input voltage and current, the reference design implements under voltage, over voltage, and over current protection. Using the reference design, a standard HID automotive bulb is able to reach steady state light output in under 150 seconds. Finally, since size is important in most ballast applications, the reference design uses planar magnetic to reach a small size of 9mm x 60mm x 80mm, commonly referred to as a “slim” ballast form factor.

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