Analyze several types of problems often occurring in LED fluorescent lamp power supply
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 The manufacturers are mainly divided into three categories: one is the factory that originally made the LED chip, and the downstream is infiltrated into the downstream.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 enters a new field and knows a little about the circuit; the third is a new factory, which knows a little about the LED power supply. LED fluorescent lamp power is the most important component of LED fluorescent lamp. If it is not properly selected, LED fluorescent lamp can not only perform its performance, or even use it normally. LED fluorescent lamp power supply and lamp 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); 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 effect can achieve the best performance. Therefore, the best way is to communicate with the power supply manufacturer first. Tailored. LED operating current General LEDs have a rated operating current of 20 mA, and some plants use the largest at the beginning, with a design of 20 mA. In fact, the working heat at this current is very serious. After many comparison tests, it is ideal to design 17 mA. LED operating voltage The recommended operating voltage for general LEDs is 3.0-3.5V. After testing, most of the work is at 3.125V, so it is reasonable to calculate according to 3.125V. LED lamp board series and parallel with wide voltage In order for the LED fluorescent lamp to operate over a wide range of input voltages (AC85-265V), the LED string parallel connection of the panel is 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 series number does not exceed 23 strings, and the number of parallel connections Do not be too much, otherwise the working current is too large and the heat is severe. It is recommended to be 6 and 8, 8 and 12, and the total current is not more than 240 mA. LED series-parallel connection with 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 is done 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. 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. Constant current accuracy The constant current accuracy of the power supply on the market is too poor. The constant current schemes such as PT4107, HV9910, BP2808, and SMD802 are popular in the market, and the error is ±8% or ±10%. The constant current error is too large, and it is generally required to be ±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. 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. 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, and the length can be long and it is easier to dissipate heat.
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