Semiconductor lighting fixtures have significant advantages such as high luminous efficiency, obvious power saving effect, long life, no pollution, and anti-vibration. They are increasingly valued by countries all over the world and are expected to replace traditional lighting fixtures in the near future. However, such lamps currently use a DC drive power supply, and a constant current circuit that converts AC power into DC power must be installed in the lamp. Although the switching constant current source is more efficient, it is still less than 90%; in addition, since the service life of the electrolytic capacitor in the switching power supply is generally less than 10,000 hours, although the life of the LED can reach 80,000 to 100,000 hours, after the power supply is damaged The lamps can not be used, which causes the LED lamps to save energy and save money, which seriously affects the promotion.
Second, the problems and solutions of pulsating constant current control
In order to ensure the conversion efficiency and reduce the volume of AC/DC power supply, non-isolated switching power supply is widely used. The conversion efficiency of this power supply is as high as 94%-95%. In this circuit, the current flowing through the LED follows the AC waveform. The change varies, and the LED flows through a pulse current of 100 (120) cycles. The current maximum is one to two times the mean. However, the luminous flux of the pulse-controlled LED is lower than that of the constant current. In the case of the same LED light source power consumption, the power flux loss is as high as 10%-20%. In addition to the loss of power supply, the efficiency of the luminaire is only 75%-85%, which is 5%-15% lower than the traditional power supply, which seriously affects the application.
Third, the reasons and solutions for low light efficiency
The amount of luminescence of the LED is related to the amount of current passing. Figure 1 is the relationship between LED power consumption and luminous flux. It can be seen that the LED input power is large, the luminescence amount is large, and the power luminescence is small, but it is not linear. As the power increases, the illuminating efficiency gradually decreases. When testing the rated power of the LED, the luminous efficiency will be reduced by 2%-3% for every 10% increase in power, and the light efficiency will increase by about 2% for every 10% reduction in power. When the power is increased to 1.5 times the rated power. The luminous efficiency will be reduced to about 86%-84% of the rated power. When the power is increased to 2 times of the rated power, the luminous efficiency will be reduced to less than 80% of the rated power, and when the power is reduced to 0.5 of the rated power. When doubled, the light efficiency will increase to about 115%-120% of the rated power.
Since the luminous flux emitted by the LED is the integral of the instantaneous power consumption and time of the LED, the AC mains is pulsating DC after bridge rectification. When there is no large capacity capacitor, the LED driving power supply adopts pulsating constant current control, and the instantaneous voltage of the power supply is high. When the LED drive voltage, the LED has a current, and when it is less, no current flows.
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For more information, please refer to the "High-tech LED - Technology and Applications" January issue
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