How to control and reap the benefits of HID lamps

Some of the significant factors that need to be considered to control and realize the benefits of HID lamps are discussed. It is essential to have a tight regulation of lamp power to minimize lamp-to-lamp color and brightness variations, as these lamps require a high voltage for ignition, current limitation during warm-up, and a constant power during running. These lamps are driven with a low-frequency AC to avoid mercury migration and to prevent damage of the lamp due to acoustic resonance. An electronic ballast circuit is needed that ignites the lamp, controls lamp power, and produces an AC lamp voltage to satisfy the lamp requirements and different operating modes. The standard circuit for controlling HID lamps includes a buck stage for controlling the lamp current, along with a full-bridge output stage for ac operation of the lamp. The full-bridge stage is necessary to produce an ac lamp current and voltage during running where it operates at 200Hz with a 50% duty-cycle.