A Novel Constant Power Control of High Frequency Electronic Ballast Applying the PLL Technique for a Metal Halide Lamp

This paper presents a new constant power control of high frequency electronic ballast for a metal halide lamp based on the phase-locked loop (PLL) technique. First, the PLL is employed as a feedback mechanism to improve the resonant frequency variations caused by lamps aging or an impedance difference between used lamps characteristics. The proposed system can adjust the operating frequency to sustain constant power for a metal halide lamp according to the impedance of the adopted lamps. Moreover, the control strategy also can be used to substantially reduce the warm-up process of a metal halide lamp. The design considerations and measured results are detailed to verify the validity of the proposed control strategy