Learn about LED Power Supply

Currently, the LED fluorescent lamp market is very active, and the manufacturers are mainly divided into three categories: one is a factory that originally made LED chips, which penetrates downstream, knows little about the circuit knowledge and the power of LED fluorescent lamps; the second type is the original one that does general lighting. The factory enters a new field and learns about circuit knowledge. The third category is a completely new factory. They used to do other products or start a new business. They have some understanding of LED power supply, and some do not understand it. The LED fluorescent lamp power supply is the most important part of the LED fluorescent lamp. If it is not properly selected, the LED fluorescent lamp cannot exert its performance and even cannot be used normally.

1, why must constant flow:

The characteristics of LED semiconductors determine their environmental impact. For example, if the temperature changes, the current of the LED increases, the voltage increases, and the current of the LED also increases. Working over a long-term rated current will greatly reduce the lifetime of the LED. The constant current of the LED is to ensure that the operating current does not change when the environmental factors such as temperature and voltage change.

2, LED fluorescent lamp power and lamp board matching:

Some customers first design the lamp board and then look for the power supply and find that it is difficult to have a suitable power supply, either the current is too high, the voltage is too small (such as I> 350mA, V <40V); or the current is too small, the voltage is too high (such as I < 40mA, V>180V), the result is serious heat generation, low efficiency, or insufficient input voltage range. In fact, choosing the best series and parallel connection method, the voltage and current applied to each LED is the same, and the power supply's effect can exert the best performance. The best way is to first communicate with the power supply manufacturers, tailor-made.

3, LED operating current:

The general LED's rated operating current is 20 mA. Some factories use them at the beginning. The design is 20 mA. Actually, this current is very hot under the current operation. After many comparison tests, the design is 17 mA. It is ideal. . The total current of N-channel parallel connection = 17*N;

4, LED operating voltage:

The recommended working voltage of general LED is 3.0-3.5V. After testing, most of the work is in 3.125V, so the calculation formula of 3.125V is more reasonable. Total voltage of M lamps in series = 3.125*M

5. Series parallel connection and wide voltage of LED light board:

To make the LED fluorescent lamp work in a wide range of AC85-265V in the input voltage range, the LED series parallel connection of the lamp panel is very important. Since the current power supply is generally a non-isolated buck power supply, when a wide voltage is required, the output voltage should not exceed 72V, and the input voltage range can reach 85-265V. That is, the number of concatenations does not exceed 23 strings. The number of parallel connections should not be too much, otherwise the operating current is too high and the heat is severe. It is recommended to be 6 and /8 and /12. The total current does not exceed 240 mA. There is also a wide voltage solution, that is, using the L6561/7527 to raise the voltage to 400V, and then step down, the equivalent of two switching power supply, cost twice as expensive, this program is not cost-effective, there is no market.

6, LED series and parallel and PFC power factor and wide voltage relationship:

At present, there are three kinds of power PFC on the market: one is without PFC dedicated circuit, the PFC is generally about 0.65; one is with passive PFC circuit, the light board is well prepared, PFC is generally about 0.92; also With one type of active active 7527/6561 circuit, the PFC can reach 0.99, but the cost of this solution is twice as expensive as the second option. So the second option is more. For passive PFC circuits: also known as valley-filled PFC circuits, the operating voltage range is half of the AC input voltage peak. If the input is 180V, its peak value is 180*1.414=254V, half of the peak voltage is 127V, and then subtract the buck pressure difference 30V, its maximum output is 90V, so the number of LED lamp beads in series is up to 28 strings. Therefore, in order to obtain a relatively large power factor, the number of concatenations of the lamp beads should not be too large; otherwise, the requirement of low voltage cannot be achieved.

7, constant current accuracy:

Some of the power supplies on the market have poor accuracy of constant current, like the PT4107/HV9910/BP2808/SMD802 solutions that are popular in the market, such as constant current solutions, the error reaches ±8% or ±10%, and the constant current error is too large. The general requirement is ±3%. With an error of 3%, 6 channels are connected in parallel, and the error of each channel is about ±0.5%. If it is a 12-channel parallel connection, the error of each channel is about ±0.25%, which is sufficient. The accuracy is too high and the cost will increase greatly. And for LEDs, 17 mA and 17.5 mA have little effect.

8, isolated / non-isolated:

General isolated power supply such as made 15W, placed in the LED lamp, the transformer is very large, it is difficult to put in. Especially for T6/T8 lamps, it is almost impossible, so the isolation can only achieve 15W, rarely exceed 15W, and the price is very expensive. Therefore, the cost-effectiveness of isolation is not high. Generally, it is non-isolated and occupies more mainstream. The volume can be made smaller. The minimum can be up to 8 mm. In fact, non-isolated security measures are done well, and there is no problem.

9, power efficiency:

Output power (output LED's voltage*output current)/input power. This parameter is particularly important. If the efficiency is low, it 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, plus an efficiency ratio of our LED. Dissipating heat will superimpose and generate higher temperatures. The lifetime of all electronic components inside our power supply will be shortened with the increase of temperature. So efficiency is the most fundamental factor that determines the life of the power supply, and the efficiency cannot be too low, otherwise it will be consumed. The heat on the power supply is too high. Generally it is more than 80%. However, the efficiency is related to the matched connection of the light board.

10, size:

The height is the main factor of the restriction, and the size of the T6 tube/T8 is generally not too high ≤ 9 mm. T10 tube height ≤ 15 mm. The length can be longer and easier to dissipate heat.