LED fluorescent lamp power solution selection

LED fluorescent lamps, as the most important lighting fixtures, will surely shine in the market with the popularity of LED lamps. LED fluorescent lamp driving power is a key factor affecting product life, and requires special attention from manufacturers.

There are three types of LED fluorescent lamp power supply manufacturers that will cause system defects in product quality: The first category is the development of LED chips or LED lights in the factory, the trend to the downstream penetration, the knowledge of LED power circuit and LED fluorescent lamp power knowledge is not much The second category is that the original factory is doing general lighting, and the knowledge of LED power circuit is not fully understood; the third category is the newly opened factory, which has limited understanding of LED power supply. Below I summarize some common problems found in practice and learning (including the network), welcome all colleagues to correct me.

1. Why should LED fluorescent lamp power supply be constant?

The semiconductor characteristics of LEDs are determined to be greatly affected by the environment. For example, temperature, LEDs are current-sensitive components. The increase in current of LEDs directly leads to an increase in heat generation. When the current exceeds the rated current for a long time, the LED chips will be in a high temperature for a long time. Shorten the life of the LED. The LED constant current power supply can ensure that the operating current does not change when the voltage and other factors change, thereby protecting the LED chip from high temperature damage. The so-called power supply is easy to destroy.

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

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 I>350mA, V<40V); or the current is too small, the voltage is too high (such as I< 40mA, V>180V), the result is severe heat, low efficiency, or insufficient input voltage range. Choosing a suitable string and parallel connection method, the voltage and current applied to each LED bead are the same, and the power supply can achieve the best performance. The best way is to communicate with the power supply manufacturer and tailor it.

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

Generally, the rated working current of LED lamp bead is 20 mA. Some factories use it at the beginning, and design 20 mA. In fact, the working heat is very serious at this current. After several comparison tests, it is designed to be 17-19 mA. It is ideal. The recommended design is 18 mAh, which guarantees that the life of the product is much higher than that of similar products, although the cost will increase by a few percentage points.

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

The recommended working voltage of the general LED lamp bead is 3.0-3.5V. After testing, most of the work is 3.125V, so it is reasonable to calculate according to 3.125V. The total voltage of M lamp beads in series = 3.125 × M

5. How wide is the series and parallel connection of the LED lamp board and the wide voltage?

Usually LED fluorescent lamps need to adapt to a wide range of input voltages such as AC85 ~ 265V, so the series and parallel connection of the LED lamp bead of the lamp board 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 to 265V. In other words, the number of series is no more than 23 strings. Do not use too many parallels, otherwise the operating current is too large 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 scheme, which is to use L6561/7527 to raise the voltage to 400V, and then step down, which is equivalent to two switching power supplies, which cost twice as much. This solution is not cost-effective and has no market.

6. What is the relationship between LED series and parallel and PFC power factor and wide voltage?

At present, there are three kinds of power supply PFCs on the market: one is without PFC dedicated circuit, and its PFC is generally around 0.65; the other is with passive PFC circuit, the light board is well prepared, and the PFC is generally around 0.92; One uses the active active 7527/6561 circuit, and the PFC can reach 0.99; the cost of the third scheme is twice as expensive as the second scheme, so there are more LED fluorescent lamps manufacturers choosing the second scheme. For passive PFC circuits: also known as valley-filled PFC circuits, the operating voltage range is half of the peak value of the AC input voltage. If the input is 180V, the peak value is 180×1.414=254V, half of the peak voltage is 127V, and the voltage drop of the buck is 30V. The maximum output is 90V, so the LED lamp bead series can be up to 28 strings. Therefore, in order to obtain a relatively large power factor, the number of series connection of the lamp bead should not be too much, otherwise, the requirement of low voltage cannot be achieved.

7, LED fluorescent lamp power supply constant current accuracy is the most appropriate?

Constant current error is generally required to be ± 3%. The constant current accuracy of some power supplies on the market is too poor. Like the popular constant current schemes such as the PT4107/HV9910/BP2808/SMD802 schemes on the market, the error reaches ±8% or ±10%, and the constant current error is too large. According to the error of 3%, 6 channels are connected in parallel, and the error of each channel is about ±0.5%. If it is 12-way parallel, the error of each channel is about ±0.25%, which is enough. The accuracy is too high and the cost will increase greatly. And for LED lamp beads, the difference between 17 mA and 17.5 mA is not too big.

8, isolated / non-isolated

Generally, if the isolated power supply is made of 15W and placed in the LED tube , the transformer is very large and difficult to put in. Especially for T6/T8 lamps, it is almost impossible, so 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.

9, LED fluorescent lamp power efficiency

Output efficiency = output LED voltage × output current / input power. This parameter is important because one of the big selling points of LED fluorescent lamps is energy saving. In addition, if the power supply efficiency is low, a large amount of heat will be emitted in the lamp tube, so that the temperature of the power supply after the temperature balance is increased, which will accelerate the failure of components in the power supply, shorten the service life of the component, and then affect the life of the power supply, and ultimately affect the life of the LED fluorescent lamp. In addition, the heat generated by the power supply will increase the temperature of the LED chip, which will cause the LED fluorescent lamp to have a light decay, which will eventually lead to a shortened life of the entire product. In summary, power efficiency is an important factor in determining the life of an LED fluorescent lamp. Generally, it is OK at 80% or more. In addition, the efficiency is also related to the matching method of the lamp panel.

10, LED fluorescent lamp power supply size

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

11. Ideas for extending the life of LED fluorescent lamps