That is a problem about LED leakage that meet with many people. Some found in the production checking test, and other found by clients while their using. The timing of the occurrence of leakage is also different. For example, certain happened in the test after the LED packing is completed; certain happened appear after a period of aging; certain appear after the customer is soldered; some appear after the customer has used it for a period of time. The specific cause of the leakage problem had been plagued by the engineers of the packaging factory. What are the reasons that led to the LED leaking? According to some researches, the most possibility reasons causing the LED leakage as follow:
- The chip is contaminated (——The most important and high-incidence problem)
- Silver glue is too high
- Wire and offset welding
- Stress
- Improper use
- Leakage of the chip itself
- Improper process, causing chip cracking
- Static electricity
- Other reasons
Problems that need to be paid attention to when installing LED power supply:
The LED street lamp power supply is precisely the top priority of the current LED development. For the related design of LED technology, there are currently a variety of solutions and unique design techniques, let's take a look one by one:
1.The reasons of the LED street lamp power supply have a constant current
The characteristics of LED lighting materials determine that they are greatly affected by the environment. For example, as the temperature changes, the current of the LED will increase, and the increase of the voltage will increase the current of the LED. Long-term work beyond the rated current will greatly shorten the life of the LED lamp beads. The LED constant current is to ensure that its operating current value remains unchanged when environmental factors such as temperature and voltage change.
2.LED street lamp power supply constant current accuracy
Some power supplies on the market have poor constant current accuracy. For constant current solutions such as popular recommended solutions on the market, the error reaches ±8%, and the constant current error is too large. The general requirement is within ±3%. According to the 3% design plan. The production power must be fine-tuned to achieve ±3% error.
3.The working voltage of the LED street lamp power supply
Generally, the recommended working voltage of LEDs is 3.0-3.5V. After testing, most of them work at 3.2V, so the 3.2V calculation formula is more reasonable. The total voltage of N lamp beads in series = 3.2* N
4.The suitable working current of LED street lamp power supply
For example, the rated working current of the LED is 350 mA. Some factories use it up at the beginning. The design is 350 mA. In fact, it is very hot to work under this current. After many comparison tests, it is ideal to design it to 320 mA. . Minimize the amount of heat generated, so that more electrical energy becomes visible light energy.
5.The distance of series and parallel connection and wide voltage of LED street lamp power supply board
To make the LED street lamp power supply work in a wide range of input voltage range AC85-265V, the series and parallel mode of the LED light board is very important. Try not to use a wide voltage, which can be divided into AC220V and AC110V as much as possible, so as to ensure the reliability of the power supply. Since the current power supply is generally a non-isolated step-down constant current power supply, when the required voltage is 110V, the output voltage should not exceed 70V, and the number of series connections should not exceed 23 strings. When the input voltage is 220V, the output voltage can reach 156V. In other words, the number of series does not exceed 45 strings. Do not connect too many in parallel, otherwise the working current will be too large and the power supply will generate serious heat. There is also a wide voltage scheme. APFC active power compensation is to use L6561/7527 to raise the voltage to 400V first, and then step down, which is equivalent to two switching power supplies. This program is only used under certain conditions.
6.Isolated/non-isolated
Generally, if the isolated power supply is made into 15W and placed in the LED street lamp power tube, the transformer is very large and difficult to put in. The space structure depends mainly on the specific situation. Generally, the isolation can only be 15W, and it is rare to exceed 15W, and the price is very expensive. Therefore, isolation is not cost-effective. Generally, non-isolated products dominate the mainstream, and the volume can be made smaller, with a minimum height of 8 mm. In fact, non-isolated security measures are in place and there is no problem. Space permitting can also be used as an isolated power supply.
7. How can LED street lamp power supply match the lamp bead board?
Some customers design the light board first, and then look for the power supply. They find that it is difficult to have a suitable power supply. Either the current is too large and the voltage is too small (such as 7X1WI "350mA, or V "20V); or the current is too small and the voltage is too high (such as I "200mA or V" 25V), the result is serious heating, low efficiency, or insufficient input voltage range. In fact, choose the most excellent series-parallel connection method, the voltage and current applied to each LED are the same, but the power supply effect can exert the best performance. The best way is to communicate with the power supply manufacturer first and tailor it. Or produce your own power supply.
8. LED series and parallel connection and PFC power factor
Isolated input AC220V high-voltage side electrolytic capacitor capacity is generally input power 1W=1UF, AC110V1W=2UF. There are three cases of power supply PFC on the market at present: the first one is without PFC without special circuit for power factor compensation, and its PF value is general Around 0.65; The second type is passive power factor compensation PFC circuit, namely passive power factor compensation lamp, also called flow-by circuit board, which is currently the most widely used and the most reliable. The PF value is generally around 0.92; still used The third type is made with active active 7527/6561 circuit, which is active power factor compensation, which is called AC220V in APFC circuit, AC110V can use electrolytic capacitors of the same capacity, choose 1W=1.5UF. The PF value can reach 0.99, but the cost of this solution is twice as expensive as the second solution and the reliability is slightly worse. So the second scheme is used more. For passive PFC circuit: it is called valley-filled PFC circuit, and its DC working voltage range is half of the peak value of AC input voltage. If the input is 220V, its peak value is 220*1.414=312V, half of the peak voltage is 156V, and the output wave is the upper half wave without the lower half wave on the non-isolated basis.
Therefore, the number of LED street lamp power beads in series should be up to 45 strings. Therefore, in order to obtain a relatively large power factor, the number of lamp beads in series should not be too small, otherwise the best working condition will not be achieved. The number of series connected on the isolated power supply is related to the number of turns of the secondary winding, which must be done. The power of the power supply must meet the output power. The smaller the working current of the electronic components in the rated voltage working range is, the longer the heat is and the longer the service life is, otherwise the service life will be shorter. LED street lamp power beads are very sensitive to the amount of AC, the higher the amount of AC, the worse the light comfort. Generally, electrolytic capacitors are used to maintain the voltage, and reduce the amount of AC voltage at the output end as much as possible. The electrolytic capacitor capacity at the bottom voltage end should not be too small. The ratio of the capacity to the output current is 1UF<1.5MA, otherwise the LED will flicker. The non-isolated input end high voltage electrolytic capacitor selection is the same as the isolated type, and the output end capacitor selection is 1UF<6MA. The electrolytic capacitor at the output end of the dimming LED power supply must meet 1UF "0.5MA".
9. LED street lamp power supply efficiency
Input power minus output power value. This parameter is particularly important. The larger the value, the lower the efficiency, which means that a large part of the input power is converted into heat and emitted; if it is installed in the lamp, a high temperature will be generated. , Coupled with the heat emitted by a luminous efficiency ratio of our LED, will superimpose to produce a higher temperature. The life of all electronic parts inside our power supply will be shortened as the temperature rises. Therefore, efficiency is the most fundamental factor that determines the life of the power supply. The efficiency cannot be too low, otherwise the heat consumed on the power supply is too large. The efficiency of the non-isolated type is higher than that of the isolated type, generally above 80%. However, the efficiency is related to the matching connection method of the light board.
10. LED street light power supply heat dissipation
The main factor of the heat dissipation scheme is that the LED street lamp power beads can greatly extend the life when they are used under overheating conditions. Generally, aluminum alloy is used, which is easier to dissipate heat. That is, the LED street lamp power bead is attached to the aluminum substrate, and the external heat dissipation area is maximized.
