LED circuit basics, why LED chips leak? What is the point of LED lighting power?

The problem of LED leakage has been encountered by many people. Some are found during production testing, and some are found when customers use it. The timing of leakage is also different. Some are found after the LED package is completed; some are appearing after being placed in the warehouse for some time; some are appearing after aging for a while; some are after the customer is soldered; some are appearing after the customer has used it for a while. The specific cause of the leakage problem has been plaguing the engineers of the packaging factory.

In the introduction, the reasons for LED leakage caused by some people are listed. According to my years of experience in dealing with LED problems and the use of LEDs, I believe that at present, the main reason for the most likely LED leakage is as follows:

(1) The chip is contaminated (-most important, high-issue problem)

(2) Silver glue is too high

(3) Wire welding

(4) Stress

(5) Improper use

(6) The chip itself leaks

(7) Improper process, causing chip cracking

(8) Static electricity

(9) Other reasons

LED street light power supply is precisely the top priority of LED development. For the related design of LED technology, there are many kinds of solutions and unique design methods. Let's take a look at it one by one;

The characteristics of LED lighting materials determine that they are greatly affected by the environment. For example, if the temperature changes, the current of the LED will increase, and the voltage will increase, and the current of the LED will also increase. Long-term operation beyond the rated current will greatly shorten the life of the LED lamp. The LED constant current is to ensure that the operating current value does not change when environmental factors such as temperature and voltage change.

The constant current accuracy of some power sources on the market is poor, and the constant current scheme such as the popular recommended scheme on the market has an error of ±8% and the constant current error is too large. The general requirement is ±3%. According to the 3% design. The production power supply should be fine-tuned to achieve ±3% error.

The recommended operating voltage of general LED is 3.0-3.5V. After testing, most of the work is at 3.2V, so it is reasonable to calculate according to 3.2V. Total voltage of N lamp beads in series = 3.2* N

For example, the rated working current of LED is 350 mAh. Some factories use it at the beginning and design 350 mA. In fact, the working heat is very serious at this current. After many comparison tests, it is ideal to design 320 mA. . Minimize heat and turn more electrical energy into visible light.

In order to make the LED street lamp power supply work in the wide range of input voltage range AC85-265V, the LED series-parallel connection of the lamp board is very important. Try not to use a wide voltage, can be divided into AC220V, AC110V as much as possible to classify, in order to ensure power supply reliability. Since the current power supply is generally a non-isolated buck constant current power supply, when the required voltage is 110V, the output voltage should not exceed 70V, and the series number does not exceed 23 strings. The output voltage can reach 156V when the input voltage is 220V. That is to say, the number of series is not more than 45 strings. Do not use too many parallel connections, otherwise the operating current is too large and the power supply is hot. There is also a wide voltage scheme. APFC active power compensation is to first raise the voltage to 400V with L6561/7527, and then step down, which is equivalent to two switching power supplies. This program is only used under certain conditions.

Generally, the isolated power supply is made into 15W and placed in the LED street lamp power supply tube. The transformer is large in size and difficult to put in. Mainly depends on the specific structure of the space, the isolation can only be 15W, less than 15W, and the price is very expensive. Therefore, the cost performance of isolation is not high, generally non-isolated is more mainstream, the volume can be made smaller, the minimum can be as high as 8 mm, in fact, non-isolated security measures are done, there is no problem. Space can also be used to isolate power.

Some customers first design the light board, then find the power supply, and find that it is difficult to have a suitable power supply, or the current is too large, the voltage is too small (such as 7X1WI) 350mA, or V "20V"; or the current is too small, the voltage is too high (such as I "200mA or V" 25V), the result is severe heat, low efficiency, or insufficient input voltage range. In fact, choosing the best string parallel connection method, the voltage and current applied to each LED is the same, and the power supply effect can achieve the best performance. The best way is to communicate with the power supply manufacturer and tailor it. Or self-produced power.

The isolated input AC220V high-voltage electrolytic capacitor capacity is generally 1W=1UF, AC110V1W=2UF. There are three kinds of power supply PFCs on the market: one is a special circuit without PFC without power factor compensation, and its PF value is generally 0.65. The two are passive power factor compensation PFC circuits, that is, passive power factor compensation lamps, also called flow-by-current circuit boards, which are the most widely used and most reliable, and the PF value is generally around 0.92; It is made with active active 7527/6561 circuit, which is active power factor compensation, called AC220V in APFC circuit. AC110V can use electrolytic capacitor of the same capacity, choose 1W=1.5UF. The PF value can reach 0.99, but the cost of this solution is slightly less expensive than the second solution. So the second option is more used. For passive PFC circuits: also known as valley-filled PFC circuits, the DC operating voltage range is half of the peak value of the AC input voltage. If the input is 220V, the peak value is 220*1.414=312V, and the peak voltage is half of 156V. On the non-isolated basis, the output wave has no lower half wave.

Therefore, LED street light power bead series number is up to 45 strings or less. Therefore, in order to get a relatively large power factor, the number of series connection of the lamp bead should not be too small, otherwise the optimal working condition will not be achieved. The number of series connection on the isolated power supply is related to the number of turns of the auxiliary winding, which must be done. The power supply must meet the output power. The smaller the operating current of the electronic component in the rated voltage operating range, the longer the end of life and the shorter the life. LED street light power beads are sensitive to the amount of AC. The higher the AC volume, the worse the light comfort. Generally, electrolytic capacitors should be used to maintain the voltage, and the voltage of the output terminal should be reduced as much as possible. The capacity of the electrolytic capacitor at the bottom end should not be too small. The ratio of the capacity to the output current is 1UF "1.5MA or the LED will flash. The non-isolated input high-voltage electrolytic capacitor is selected in the same way as the isolated type, and the output capacitor is 1UF "6MA." Dimming LED power supply at the output of the electrolytic capacitor to meet 1UF "0.5MA.

This parameter is especially important for input power minus output power. The higher the value, the lower the efficiency. This means that a large part of the input power is converted into heat. If it is installed in the lamp, it will produce a very high temperature. Together with the heat generated by one of our LEDs, it will superimpose to produce a higher temperature. The life of all electronic components inside our power supply will decrease with increasing temperature. Therefore, efficiency is the most fundamental factor in determining the life of the power supply. The efficiency cannot be too low, otherwise the heat consumed on the power supply is too large. The non-isolated efficiency is higher than the isolation type, generally more than 80%, but the efficiency is related to the matching method of the lamp board.

The main factor of the heat dissipation scheme is that the LED street lamp power supply bead can be used for extended life under the hot condition, and the aluminum alloy is generally used, which is more convenient for heat dissipation. That is, the LED street lamp power supply bead is attached to the aluminum substrate, and the external heat dissipation area is maximized.   888888888888888888888888888888888888888888