LED driver circuit overview
1. Overview?? ??
The LED is a solid light source. When a forward voltage is applied across it, minority carriers and majority carriers in the semiconductor recombine, and the excess energy emitted will cause photon emission. Different materials can be used to make LEDs of different colors. As a new light source, in recent years, major companies and research institutes are in the ascendant to research LEDs, which has greatly improved their light efficiency. Lumiled has developed and produced white LEDs with luminous efficacy up to 90Lm/W, which has reached incandescent lamps. s level. Compared to incandescent lamps, LEDs have many advantages in performance.
With the further development of LED research, its light efficiency will be further improved, and its cost will be reduced step by step. In the near future, LED will replace incandescent lamps and even fluorescent lamps and become a major illumination source in the 21st century. trend. ?ãŠãœbr>
The new light source calls for new high-power LED drivers. Tianxiaming Technology has started research on LED driver circuits in recent years, and has independent intellectual property rights. It has occupied the world's leading position in this research and development field.
?� 2. LED driver circuit overview?
Unlike electronic ballasts for fluorescent lamps, the main function of the LED driver circuit is to convert the AC voltage to a constant current source and simultaneously match the voltage and current of the LED. ?ãŠãœbr>
The forward volt-ampere characteristics of the LED are shown in Figure 1:
Therefore, the digital model of the volt-ampere characteristics of the LED can be expressed by the following formula: ãŠã¶F=Vturn-on+RsIF+(ΔVF/ΔT)(T-25°C) (1)?ãŠãœbr>
Where Vturn-on is the starting voltage of the LED? ãŠã²s is the slope of the volt-ampere curve? ãŠã´ ambient temperature? ãŠã†ã¶F/ΔT is the temperature coefficient of the LED forward voltage, which is typically -2V for most LEDs. /°C. ?ãŠãœbr>
From the volt-ampere curve and digital model of the LED, the small change of the forward voltage of the LED after the forward conduction will cause a large change of the LED current, and the environmental temperature, LED aging time and Other factors will also change the electrical influence of the LED. performance. The light output of the LED is directly related to the LED current. Therefore, the LED driving circuit can control the LED current in the case of fluctuations in input voltage and ambient temperature. Otherwise, the LED light output will follow the input voltage and temperature. Changes and changes, and if the LED current is out of control, long-term operation of the LED at high current will affect the reliability and life of the LED, and may fail.
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