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The Key To The Design Of LED Fluorescent Light Power Supply

At present, the LED fluorescent lamp lighting market is relatively active. LED drive power supply manufacturers are mainly divided into three types: the first type is the factory that develops LED chips or LED lamps, and penetrates downstream; the second type is the factory that originally made Traditional LED high bays light ; The third category is completely newly opened factories, they used to do power supply or other products or new ventures.

The LED fluorescent lamp power supply is a very important part of the LED fluorescent lamp. If it is not selected properly, the LED fluorescent lamp will not be able to perform as it should, and it may even not be able to be used for normal lighting. Below I have made some small suggestions on LED fluorescent lighting for your reference.

1. Why must the LED fluorescent lamp power supply be constant current?

The characteristics of LED semiconductors determine that they are greatly affected by the environment. For example, as the temperature rises, the current of the LED will increase; as the voltage increases, the current of the LED will also increase. Long-term operation exceeding the rated current will greatly shorten the service life of the LED. The LED constant current is to ensure that its operating current remains unchanged when environmental factors such as temperature and voltage change.

2. How can the LED fluorescent lamp power supply match the light panel?

Some customers design the 250W Per Modular High Power LED Floodlights board first, and then find the power supply, and find it difficult to have a suitable power supply, either the current is too large and the voltage is too small (such as I>350mA, V<40V); or the current is too small and the voltage is too high (such as I< 40mA, V>180V), the result is serious heating, low efficiency, or insufficient input voltage range. In fact, if you choose the best series-parallel connection, the voltage and current applied to each LED will be the same, but the effect of the power supply will be the best. The best way is to communicate with the power supply manufacturer first and make a tailor-made one.

3. What is the most suitable working current of the LED fluorescent lamp power supply?

Generally, the rated working current of LED is 20 milliampere, some factories use it up at the beginning, and design 20 milliampere, in fact, the work heat is very serious under this current, after many comparison tests, it is more reasonable to design it as 17-19 milliampere Ideally, the recommended design is 18mA.

4. What is the working voltage of the LED fluorescent lamp power supply?

Generally, the recommended working voltage of LED is 3.0-3.5V. After testing, most of them work at 3.125V, so the calculation formula of 3.125V is more reasonable. The total voltage of M lamp beads in series = 3.125*M

5. How wide is the series-parallel connection and wide voltage of LED light panels?

To make the LED fluorescent lamp work in a relatively wide input voltage range (full voltage) AC85-265V, the series-parallel connection of LEDs on the lamp board is very important. Since the current power supply is generally a non-isolated step-down 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 to say, the number of series connection does not exceed 23 strings. The number of parallel connections should not be too large, otherwise the operating current will be too large and the heat will be severe. It is recommended to use 6 parallels/8 parallels/12 parallels. The total current should not exceed 240mA as well. There is also a wide-voltage solution, which is to use L6561/7527 to raise the voltage to 400V first, and then step down the voltage. It is equivalent to two switching power supplies, and the cost is twice as expensive. This solution is not cost-effective and has no market.

6. What is the relationship between series and parallel connection of LEDs, PFC power factor and wide voltage?

At present, there are three kinds of power supply PFC in the market: one is without PFC special circuit, and its PFC is generally around 0.65; the other is with passive PFC circuit, the lamp board is well prepared, and its PFC is generally around 0.92 One is made with an active active 7527/6561 circuit, and the PFC can reach 0.99, but the cost of this solution is twice as expensive as the second one. So the second option is more common. For passive PFC circuit: also known as valley-filling PFC circuit, its operating voltage range is half of the peak value of the AC input voltage. If the input is 180V, its peak value is 180*1.414=254V, half of the peak voltage is 127V, and then minus the step-down voltage difference of 30V, the maximum output is 90V, so the maximum number of LED lamp beads in series is 28 strings. Therefore, in order to obtain a relatively large power factor, the number of series connection of lamp beads should not be too many, otherwise, the requirement of low voltage will not be met.

7. What is the most suitable constant current accuracy for LED fluorescent lamp power supply?

The constant current accuracy of some power supplies on the market is too poor, such as the popular PT4107/HV9910/BP2808/SMD802 solutions on the market, the error reaches ±8% or ±10%, and the constant current error is too large. The general requirement is within ±3%. According to the 3% error, if 6 channels are connected in parallel, the error of each channel is about ±0.5%. If 12 channels are connected in parallel, the error of each channel is about ±0.25%. This accuracy is enough. If the accuracy is too high, the cost will be greatly increased. And for LEDs, 17 mA and 17.5 mA have little effect.

8. Isolation/non-isolation

If the general isolated power supply is made into 15W and placed in the LED lamp tube, the transformer is very bulky and it is difficult to put it in. Especially for T6/T8 lamps, it is almost impossible, so the isolated ones can only achieve 15W, and the ones exceeding 15W are rare, and the price is very expensive. Therefore, the price-performance ratio of isolation is not high. Generally, non-isolation is the mainstream, and the volume can be made smaller, and the minimum height can be 8mm. In fact, there is no problem if non-isolation safety measures are taken well.

9. LED fluorescent lamp power efficiency

Output power (output LED 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 and emitted; if it is installed in the lamp tube, it will generate a very high temperature. Dissipating heat will superimpose to generate 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 should not be too low, otherwise the heat consumed on the power supply will be too large. Generally, more than 80% is enough, but the efficiency is related to the matching connection method of the light board.

10. LED fluorescent lamp power supply size

Height is the main factor of limitation, generally used for T6 tube/T8 size requires that the height should not be too high ≤ 9mm. The height of the T10 tube is ≤15 mm. The length can be longer, which is easier to dissipate heat.

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