The relationship between led lamps and led power supplies
Many high-power LED packaging factories now encapsulate many individual LEDs in parallel and in series to produce a single 20W, 30W or 50W or 100W or even higher power LED, even though these individual LEDs are packaged before they are packaged. They are strictly selected and matched, but because the internal quantity is small, there are dozens of individual LEDs, and as many as hundreds of individual LEDs, the packaged high-power LED products still have great differences in voltage and current. Compared with a single LED (generally a single white, green, and blue light working voltage is 2.7-4V, a single red, yellow, and orange light working voltage is 1.7-2.5V), the parameter difference is bigger! (Remind that the newly launched LED lighting factory can not ignore the packaging quality of the LED light source) Some manufacturers, in order to reduce the cost of the product, use constant voltage to drive the LED (the low-grade high-power LED lamps produced by some factories use a constant voltage power supply) One or several high-power resistors are connected in series to work; the worst driving power is the voltage driving method of using resistors and capacitors to step down), which also brings a large difference in the brightness of each LED during mass production, and the LED cannot work at the maximum A series of problems such as good condition, short life span, and severe fever.
If the LED lamps you buy are brighter when the voltage is normal (for example, when the mains power is AC220V), but when the voltage is relatively low (for example, when the mains drops to AC190V), you feel that the brightness drops a lot, then you can be sure of the quality of the LED lamps you buy It is not good. The quality of the LED drive power used by this lamp is relatively poor.
Maybe some people will say: Are these words you said are exaggerated? Actually no, if you don’t believe me, please look at the LED indicator lights installed next to the highway to understand (to observe at night, the impression will be more profound), almost; One out of ten is defective; either there are few strokes indicating the number (the result of damage to some LEDs), or it is bright and dark at the same time...Why is there such a bad phenomenon? This is the choice of low quality The result of LED driving power to drive the LED. Constant current source drive is the best way to drive LEDs. It uses constant current source drive instead of connecting a current-limiting resistor in the output circuit. The current flowing through the LED is not affected by external power supply voltage changes, environmental temperature changes, and discrete LED parameters. In this way, the current can be kept constant and the various excellent characteristics of LED can be fully utilized.
The LED constant current power supply is used to supply power to the LED lamps. Since the current flowing through the LED is automatically detected and controlled during the working period of the power supply, there is no need to worry about excessive current flowing through the LED at the moment of power-on, and there is no need to worry about the load short-circuiting. Bad power supply.
For 0.5W or 1W or 3W or more power LEDs, the best driving method is: connect all these high-power LEDs in series instead of parallel; for low-power LEDs (such as common LEDs driven by 20 mA) Use the method of series-parallel to drive, but the number of parallel circuits should not be too many, otherwise the consistency of the product will be greatly reduced.
Using constant current drive mode, it can avoid current changes caused by the change of the LED forward voltage, and at the same time, the constant current makes the brightness of the LED stable, and it is also convenient for LED lighting manufacturers to ensure product consistency when implementing mass production. Therefore, many manufacturers have Fully aware of the importance of driving power, many LED lamp manufacturers have given up the constant voltage method, and chose a slightly higher cost constant current method to drive LED lamps. Some manufacturers worry that the use of electrolytic capacitors for the power drive board will affect the life of the power supply. It is actually a misunderstanding. For example, if you choose a high-temperature electrolytic capacitor with a 105 degree Celsius and a lifetime of 8000 hours, according to the prevailing electrolytic capacitor life estimation method, "Every 10 degree decrease , Life is doubled", then it has a working life of 16,000 hours in a 95 degree environment, 32,000 hours in an 85 degree environment, and 64,000 hours in a 75 degree environment. If the actual working temperature is lower, Then the life span will be longer! From this point of view, as long as the selection of high-quality electrolytic capacitors has no effect on the life of the driving power supply!
There is another point worthy of attention from LED lighting companies: LED will emit a lot of heat during the working process, which will cause the tube core junction temperature to rise rapidly. The higher the LED power, the greater the heating effect. The increase in the temperature of the LED chip will lead to the performance of the light-emitting device. According to the experimental test, the luminous flux decreases by 3% every time the temperature of the LED itself rises by 5 degrees Celsius. Therefore, the LED lamp must pay attention to the heat dissipation of the LED light source itself, when possible. Try to increase the heat dissipation area of the LED light source itself, and reduce the operating temperature of the LED itself as much as possible. If conditions permit, it is best to separate the power supply part from the light source part. It is not advisable to blindly pursue a small size and ignore the working temperature of the lamp and the power supply. On the surface, the appearance is small and exquisite, but the life span is shorter and the light decay is increased. It is a typical "small loss due to small loss".
