When the led light is turned on, it only emits weak light and does not shine. Professional lighting electronic engineer tells you how to deal with it?

When the led light is turned on, it only emits weak light and does not shine. Professional lighting electronic engineer tells you how to deal with it? One case is that the LED driving power supply is damaged (suddenly damaged), and the leakage current of uA level flows through the LED lamp beads and only emits weak light. The solution is to repair the LED driving power supply or replace the LED driving power supply with the same or similar output voltage and current parameters; Another possibility is that the LED lamp has been used for a long time, which is caused by serious light decay, and it seems that there is only weak light, but this situation is gradual, not sudden, and the LED lamp still consumes the same power as the original. In this case, our maintenance direction is to replace the light source board and replace it with a new light source board with the same voltage and current parameters, which can almost restore or approach the original brightness (depending on the quality of the newly replaced light source board). We will tell you the causes and consequences of the two failures and the corresponding reliable solutions.

1. LED lamp current and brightness under normal conditions Under normal circumstances, according to the power of the LED light, the LED driving power supply will output a constant DC current, and the output voltage can be adjusted slightly within a certain range. At this time, we can see that the LED light is normal brightness. The current flowing through the LED lamp varies according to the power of the LED lamp and the number of strings and parallels. For example, the more common LED lamp is about 1.2 meters and 18W. When the number of strings and parallels of the LED lamp is 2 and 48 strings, then The current is about 120mA, and the voltage across the LED lamp bead is about 140V; if the LED lamp bead is 4 parallel and 24 strings, the current of about 18W at 1.2 meters changes by 240mA, and the voltage across the LED lamp bead is about 72V; in addition, common LEDs Bulbs, such as 5W, are usually made with 7 lamp beads of 9V/1W. The voltage across the LED lamp beads is about 63V, and the current flowing through is about 80mA. Of course, there are also high-power LED lights of several hundred watts, and the current flowing through them is several amperes. But the current flowing through the lamp beads, according to the current mainstream LED lamp beads in the market, for example, the 0.2W 3V 2835 lamp beads used for LED fluorescent lamps usually have a rated current of 60mA, and the LED lamp beads used for bulb lamps The current of 1W 9V 2835LED lamp beads is usually rated at 100mA, and the current of 1W 6V 3030 lamp beads usually used for high-power lamps is 150mA. The output voltage is determined by the number of lamp beads, and the output current is determined by the LED. The number of lamp beads in parallel is determined. Usually in engineering, in order to prolong the life of LED lamps, appropriate derating will be used.
2. One of the reasons why the led light only emits weak light when it is turned on: the LED drive power supply is damaged (1) When the quality of the electrolytic capacitor of the LED driving power supply is poor, the electrolyte is dry, the capacitance value is greatly reduced, the power supply of the LED constant current chip is seriously insufficient, and the LED constant current chip cannot enter the constant current working state, there will be two situations. , one situation is: the led light keeps flashing after it is turned on, and the other situation is that the led light mentioned in this article only emits weak light when it is turned on. In this case, we can try to replace the electrolytic capacitor, which is usually only applicable to When the electrolytic capacitor is directly connected after the rectifier bridge. As shown below:

The led light only emits weak light when it is turned on-LED drive power supply schematic diagram-front-end electrolytic capacitor schematic

(2) As shown in the picture above, if the LED constant current driver chip in the picture is selected in order to save money, the internal resistance of the chip is large, the allowable current is small, the margin is not enough, the heat is too high, and the LED driver chip is damaged. There will be a situation where the LED driver power supply is damaged.

(3) When the LED drive power supply does not enter the normal constant current working state, but the rectifier bridge stack of the front stage is still in the normal working state, at this time, a DC voltage of about 330V passes through the LED lamp beads and passes through the lamp board (light board). The insulation is not absolutely infinite, it is at the level of megohms. When high voltage is applied, there will be a microampere current flowing), forming a microampere small current, which flows through the LED lamp beads. , we can see in the dark that the led light only emits weak light when it is turned on. This small current of microampere also exists normally when it is working normally, but it exists at the same time as our normal working current. It's just that when the large current that works normally no longer exists, the weak light emitted by this tiny current can be seen in the dark.

3. The second reason why the led light is turned on and only emits weak light and does not light up: the LED lamp bead has serious light failure In this case, either replace the LED lamp board with the same voltage and current parameters, or directly replace the new LED lamp, otherwise the electricity is wasted. LED lamps have a lifespan, and LED lamp beads also have a lifespan. The light emission of LED lamp beads will continue to decay with the increase of use time, and become weaker and weaker until people can’t stand it and replace it. The light decay of LED is usually the same as Temperature is closely related, the higher the temperature, the faster the decay. The essence of LED light decay is: the silver-plated layer of the LED lamp bead will gradually oxidize with the penetration of oxygen and moisture, the plastic bracket of the LED lamp bead will gradually turn yellow, resulting in lower and lower reflectivity, and the surface glue of the LED lamp bead will penetrate through. The light rate will be lower and lower, and the LED lamp bead is in a high temperature environment, and these three changes will be exacerbated. Generally, every 10 degrees increase of the LED lamp bead means that the lifespan of the LED lamp bead is reduced by about 10,000 hours. The current LED lighting market and supply and demand relationship, low-price strategy, and low profits for manufacturers can only reduce the light efficiency of lamp beads, reduce heat dissipation aluminum materials, use cheaper chips and electrolytic capacitors, these are led lights only emit weak light when turned on. The main reason for the light. With the current technical level of the LED lighting industry, LED lights only emit weak light and do not light up when turned on. Normally, this situation should only occur after 5 years, 8-10 years or even longer. However, the current level of domestic LED lamps, limited by price and competition, is basically at the second-class level. Many LED lamps will be turned on after half a year, or even some 15 days, or about a month. .
4. When buying LED lamps, how to avoid buying LED lamps that quickly turn on LED lamps that only emit weak light and do not shine, and buy LED lamps of good quality. LEDs will appear after 5 years, or 8-10 years later What if the light is turned on and only dimly lit? Manufacturers are required to supply LED lamp beads with high luminous efficiency (such as finished products above 150Lm), low light decay, high temperature resistance, or a large power margin (such as 0.5W lamp beads used as 0.2W derating); good heat dissipation of lamps, such as Buy LED aluminum-plastic light tubes instead of LED glass light tubes. The bulbs also use aluminum shells instead of plastic shells. For high-power lamps, large-area heat sinks should be used to ensure that LED lamps work at low temperature; use long-life lamps. The LED drive power supply can usually require a five-year warranty. Such LED lamps will basically not have the situation that the LED light is turned on and only emits weak light and does not shine. Biwei Lighting is the supplier of high-efficiency, long-life LED lamps. Users who need bulk purchases are welcome to consult.