At present, the LED fluorescent lamp market is very active. The manufacturers are mainly divided into three categories: one is the factory that originally made the LED chip , and the downstream is infiltrated into the downstream. There is not much knowledge about the circuit knowledge and the LED fluorescent lamp power supply; the second category is the original ordinary lighting. The factory, entering a new field, knows some about circuit knowledge; the three types are completely new factories. They used to do other products or new ventures, and they have some understanding of LED power supply , and some don’t understand. The LED fluorescent lamp power supply is the most important component of the LED fluorescent lamp. If the LED fluorescent lamp is not properly selected, the LED fluorescent lamp cannot perform its performance or even function normally. In the process of cooperation with customers, I found some misunderstandings, and here are some suggestions for customers to choose.
1. Why must constant current: The characteristics of LED semiconductors determine that they are greatly affected by the environment. For example, if the temperature changes, the current of the LED increases, and the voltage increases, and the current of the LED also increases. 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. LED fluorescent lamp power supply and light board matching: 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); The current is too small and the voltage is too high (such as I<40mA, V>180V), resulting in severe heat generation, 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.
3. LED working current: The rated working current of the general LED is 20 mA. Some factories use it at the beginning, and design 20 mA. In fact, the working heat at this current is very serious. After many comparison tests, it is designed into 17 mA is ideal. The total current of the N parallel connection = 17 * N;
4. LED working voltage: The recommended working 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. Total voltage of M lamp beads in series = 3.125* M
5. Series and Parallel Connection of LED Light Board and Wide Voltage: In order to make the LED fluorescent lamp work in the wide range of input voltage range 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 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 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. The relationship between series and parallel connection of LED and PFC power factor and wide voltage; currently there are three kinds of power supply PFC on the market: one is without PFC dedicated circuit, its PFC is generally around 0.65; one is with passive PFC circuit The PFC is generally around 0.92. It is also made of an active active 7527/6561 circuit. The PFC can reach 0.99, but the cost of this solution is twice that of the second solution. . 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. Constant current accuracy: The constant current accuracy of some power supplies on the market is too poor. Like the popular PT4107/HV9910/BP2808/SMD802 schemes on the market, the error reaches ±8% or ±10%, and the constant current error Too big. 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: If the general 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. 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. Dissipating heat will superimpose to produce higher temperatures. The life of all electronic components inside our power supply will decrease with the increase of temperature. Therefore, efficiency is the most fundamental factor determining the life of the power supply. The efficiency should not be too low, otherwise it will be consumed. The heat 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. Dimensions: Height is the main factor of limitation. Generally, the size of 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.
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