Analysis And Design Of An Electronic Ballast For The Cold Cathode Fluorescent Lamp(CCFL)

The Cold Cathode Fluorescent Lamp (CCFL), one of novel gas discharge lamps, which presents good performances such as high lightness, longevity of service, low power consumption, instantaneous startup and so on, is one of the current very efficient light sources for background illumination (backlight) of display units. The merits held by CCFL tally with the advocate for national "green illumination" engineering, which makes it hold a very important position in the future daily illumination field.CCFL hardly has any difference on the working principle with Heat Cathode Fluorescent Lamp (HCFL) except for its higher working voltage and lower working current. But how to drive the minitype light tube of CCFL is a very tough job because of its special demands on the arc and working voltages. For solving the problem, the paper aims to work out the electronic ballast device matching with CCFL.This paper first introduces the luminescence principle of CCFL, its investigation background and actuality, and its development trend. This study also analyzes and compares several topology frames in common use including Royer, half-bridge and full-bridge topologies; designes and experiments with the half bridge topology.Current harmonic and power factor are two of the very important technical indexes, and the power factor correction (PFC) and half-bridge inverter circuit topology are commonly used in modern high power factor electronic ballasts. So the paper expatiates on the principle and characteristic of PFC circuit and gives the circuit design method of PPFC and APFC. The results of contrast analysis indicate that the design satisfies the expected objective.The design approach for CCFL borrows some ideas for designing electronic ballast of fluorescent lamp, in which the scheme of adaptor plus inverter is adopted. Compared with the conventional scheme of low-voltage input, this design owns the merits like smaller volume and higher efficiency. Aimed at actual application of CCFL, the half-bridge self-excited oscillation electric ballast consisted of separated elements is supplied with household electricity. The working principle, the design process and the guide for selection of elements are presented; a sample product is also developed and validated.After studying the capability, the performance, the characteristics and the working principle of UBA2070 used in the CCFL half-bridge driver are investigated, and a driver circuit of 2-tube CCFL adopting the UBA2070 chip is designed. The structure of main circuit given in this design realizes the functions such as "soft start", light regulation, overvoltage (protection), overcurrent protection and so on. The experimental measuring results show that the electric ballast has the features of continuous line current, adequate power factor correction and reasonable total harmonic distortion (THD), achieve the design objective.