In recent years, with the rise of the global LED commercial lighting market, many LED manufacturers including China have placed LED commercial lighting products at an important position in market development. In particular, due to recent high-efficiency, long-life, high-power factor, flexible expansion, and dimming requirements for LED lighting products in major markets such as Japan, Europe and the United States, LED driver ICs and power supplies are facing a new revolution. . Therefore, in the next two years, the proportion of smart dimming of LED lamps, especially in commercial lighting, is expected to increase rapidly. The main challenge currently is that the price of LED light sources is declining, but the driving electronics technology has not been greatly innovated, the price has been high and the cost is under pressure. Secondly, since the LED lighting adopts the current driving mode, and the existing dimmers are mostly voltage dimming, the compatibility challenge is also quite large. In addition, the trend of thinning the power supply also requires a smaller size of the LED driver . As a consumer, LED lighting products need to provide consumers with a unique sensory experience with driver IC dimming technology. According to the survey and analysis report, the US market currently has a large demand for dimming products, and almost 100% are dimming products. The European market is a little less, but it also accounts for a large proportion. In addition, smart LED bulbs are likely to be commercially available on a large scale this year. Most of these dimming products are used with thyristor dimmers. Therefore, research on thyristor dimming LED lighting products makes sense. 1. Introduction to thyristor dimming Analysis of traditional incandescent lamps, halogen lamps and other dimming systems, because incandescent lamps and halogen lamps are purely resistive devices compared to LED lamps, which means that its current waveform and voltage waveform are always the same, when used When the silicon is controlled to dim, the input voltage waveform deviates from the sine wave due to the change of the conduction angle of the thyristor, that is, the effective value of the input voltage is changed, and the dimming purpose can be achieved. Its electrical schematic is shown in Figure 1. The dotted line is the thyristor dimmer switch mounted on the wall. The resistance between ab is the incandescent lamp load. So the thyristor switch is directly connected to the load. Figure 1 Schematic diagram and waveform diagram of thyristor dimming The thyristor potentiometer has a switch connected to the input of n for controlling the switch of the lamp. During the conduction process of the thyristor, changing the voltage division ratio of the internal adjustable resistor and changing its conduction angle, the effective value of the output voltage can be changed, thereby realizing the dimming function. In addition to thyristors, there are transistor front and rear edge dimming technologies, and the basic principles are similar. 2, the shortcomings and problems of thyristor dimming When dimming with a thyristor, there are still a series of problems as follows. (1) During the dimming process, as the internal conduction angle changes, the input voltage sine wave is destroyed by the thyristor, thereby reducing the power factor value (PF), usually PF is lower than 0.5, and during dimming, As the conduction angle is smaller, the power factor value is getting lower and lower (only 0.25 for 1/4 brightness). (2) As above, the input voltage sine wave is destroyed, and the non-sinusoidal waveform increases the harmonic coefficient. (3) The input of a non-sinusoidal voltage waveform in the LED driver circuit generates a severe interference signal (EMI) on the line.
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