High Frequency Operation of Metal Halide Lamp with Frequency Control

Abstract

When a metal-halide lamp is operated by a sinusoidal wave of 10k to 100kHz, arc instability caused by acoustic resonance occurs. The frequency regions for stable operation are narrow and vary with the operating condition. Therefore, it is difficult to operate the lamp at high frequency with a fixed frequency.
This paper presents a ballast for a metal-halide lamp. When the fluctuation of lamp voltage is large because of instability, the operating frequency of the inverter moves back and forth between f_max and f_min, searching for a stable frequency. If the operating frequency coincides with a stable frequency and the lamp voltage fluctuation becomes small, so the operating frequency is maintained. Thus, the lamp operates at some stable point between _max and f_min.
Experiments performed with metal-halide lamp M100·L and stable operation at frequency range of 2025kHz is confirmed.
This procedure reduces the interference with communication systems compared with square wave operation or frequency modulation.