Electronic Ballast for 119W UV Lamp Controlled by Microprocessor

Abstract

This paper presents a method for controlling 119W digitized ultraviolet (UV) lamp electronic ballast with chip microprocessor. With this method, power closed loop can be easily realized and protection can also be carried out correctly when malfunctions including open-circuit and short- circuit state occur. Experimental results show that UV-lamp ignites reliably, harmonic content can be controlled below 10% and efficiency of the ballast can be higher than 94%. Keywords-- Ballast, UV lamp, Microprocessor I. INTRODUCTION Ultraviolet (UV) lamp is more and more widely used in the fields of waste water treatment, medical treatment and so on owing to its strong bactericidal effect. The UV-lamp used here is common cold cathode UV-lamp, and it's mainly used for disinfection of air and surface of object. Because of improving processing technique, cold cathode UV-lamp has longer service life and higher radiance than hot cathode UV- lamp. The ballast studied here is used for waste water treatment. The lamp voltage of code cathode UV lamp is very high, so its lamp current is very small which makes it difficult to do power closed loop. And because the lamp is in the water, the down-lead of the lamp is usually very long which makes igniting and protecting difficult. Nowadays, different kinds of machines tend towards intellectualized. And it's not only limited to illumine the lamp for the ballast, but required to estimate the ballast's working condition to keep the ballast and the lamp safe, what is more important is to prevent industrial accident, so sixpenny 8-bit single-chip microprocessor becomes a reasonable choice. The MCU used here is MC68HC908 which is produced by Freescale and has extremely high reliability. With this kind of chip microprocessor, steady ignition, estimation of open- circuit and short-circuit state, power closed-loop control can be realized easily. The main circuit here is resonant circuit which uses the topology of LCC, but resonance point of triple-frequency harmonics is used here instead of fundamental wave, so voltage stress and current stress of passive network can be decreased a lot because the energy of triple-frequency harmonics is relatively much lower than fundamental wave. This paper also presents a kind of drive circuit which can supply unerring switching signal and adjust dead band time properly.