1 Introduction In recent years, high-frequency fluorescent electronic ballasts have been gradually accepted by people for their high efficiency, small size, light weight, no stroboscopic, long lamp life and so on.
China's research and development of electronic ballasts was in the late 1980s and early 1990s. In the early stage, in order to save costs, many manufacturers chose a simple topology, performance indicators often fail to meet national standards, and are extremely vulnerable, which undoubtedly caused more obstacles to the popularity of electronic ballasts. At present, some people directly apply foreign advanced circuit topologies, resulting in complicated design methods, and even some are not suitable for working under the 220V/50Hz power grid. With the increasing attention of energy-saving issues, high-performance fluorescent electronic ballasts need to increase the dimming function, reducing the output power in the case of unnecessary full power output, not only saving energy, extending the life of the lamp, but also To the purpose of transforming visual effects. Therefore, it is extremely urgent to develop high-performance, more close-to-light characteristics and full-featured electronic ballasts.
2 Design Points 2.1 Overview The dimming function actually refers to the function of adjusting the output power on the lamp. When the lighting device does not require full power output, studies have shown that applying a dimming system can save 50%.
In the traditional non-dimming system ballast design, since the output power is also constant when the lamp is operating at high frequencies and stable, it can be approximated that the lamp is a constant resistance. When the grid voltage fluctuates, or the lamp current and lamp voltage change due to other reasons, that is, the lamp voltage, the lamp current RMS value, and the lamp power change, the lamp can be stably operated near the rated point by the closed-loop control. The resistance does not change much. However, the design becomes complicated in the dimming mode. If the lamp is still equivalent to a pure resistive load, considerable deviation will occur because the negative resistance characteristic exhibited by the fluorescent lamp at different dimming levels is different. Therefore, designing a dimming electronic ballast cannot be equivalent to a simple resistive load.
In recent years, the design process of power electronic devices has been greatly simplified due to the use of computer-aided design, and more circuit work information can be obtained. Commonly used simulation softwares include PSPICE, MATLAB, etc., and PSPICE is mostly used in the design of power electronic devices. Therefore, the establishment of a PSPICE model of fluorescent lamps has become an urgent problem to be solved.
2.2 Modeling of Fluorescent Lamps There are two main methods for modeling fluorescent lamps. One is physical modeling, which is based on the physical discharge phenomenon of lamps. However, this modeling method involves more complicated equations and many variables. Not suitable for circuit simulation; the other is the method of curve fitting, which uses the V-I characteristic curve of the lamp to model, according to the experimental results, using the curve equation with the undetermined coefficient to approximate, some of which use the cubic curve equation Also, use exponential curve equations, parabolic curve equations, or even linear equations to fit.
The PSPICE model can be either a static model or a dynamic model. The static model needs to calculate the impedance values ​​of the lamps at different working points, and then perform the distribution simulation. Usually such models are simple to set up, but the application is very inconvenient. The dynamic model needs to reflect the impedance value presented by the lamp directly when the working point changes, including its startup process. Such a model is usually called a dimming model, which is very suitable for dimming electronics. Ballast design. Figure 1 is a PSPICE dynamic model of a fluorescent lamp. It is based on the exponential curve, which is built for the 32W-T8 lamp.
Figure 4 Main circuit topology of electronic ballast for dimming fluorescent lamps
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