Some factors to be aware of in the design of LED lamp power supply

At present, the LED fluorescent lamp lighting market is relatively active. The LED driver power supply manufacturers are mainly divided into three types: the first is to develop a factory that makes LED chips or LED lights, and the downstream is infiltrated; the second type is the factory that is used for general lighting. The third category is a completely new factory that used to be a power source or other product or a new venture.

LED fluorescent lamp power supply is a very important part of LED fluorescent lamp. If it is not properly selected, LED fluorescent lamp can not play its proper performance, and may even not be able to use normal lighting. Here are some small suggestions for LED fluorescent lighting power supply for your reference.

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

The characteristics of LED semiconductors are determined to be greatly affected by the environment. For example, if the temperature rises, the current of the LED will increase; when the voltage increases, the current of the LED will also increase. Long-term operation beyond the rated current will greatly shorten the service life of the LED. The LED constant current is to ensure that its operating current does not change when environmental factors such as temperature and voltage change.

2. How can 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.

In fact, choose the best string parallel connection method, the voltage and current applied to each LED are the same, and the power supply can achieve the best performance. The best way is to first 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 is 20 mA. Some factories use it at the beginning. The design is 20 mA. In fact, the working heat is very serious at this current. After several comparison tests, the design is 17-19 mA. Ideally, the recommended design is 18 mA.

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

The recommended operating voltage of general LED 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 the M lamp bead series is 3.125*M.

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

In order to make the LED fluorescent lamp work in a wide range of input voltage range (full voltage) AC85 ~ 265V, the LED series and parallel connection of the light 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 85-265V. In other words, the number of series is no more than 23 strings.

Do not use too many parallel connections, 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 first raise the voltage to 400V with L6561/7527, and then step down, which is equivalent to two switching power supplies, which is twice as expensive. 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 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.

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

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. The general requirement is ±3%.

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 LEDs, 17 mA and 17.5 mA have little effect.

8. Isolation / non-isolation

Generally, if the isolated power supply is made of 15W and placed in the LED tube, the transformer is large in size 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 power (output LED voltage * output current / input power). This parameter is especially 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 a light efficiency ratio of our LED. When the heat is dissipated, 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 a power supply. The efficiency cannot be too low, otherwise the heat consumed on the power supply is too large. Generally it can be more than 80%, but the efficiency is related to the matching method of the light board.

10.LED fluorescent lamp power supply size

Height is the main factor limiting, and the size required for T6 pipe/T8 is generally 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.

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