This technical article introduces six factors to consider when designing LED fluorescent lamp power supply.

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

LED semiconductor features determine that it will be greatly influenced by the environment, such as temperature and the current will increase; with the increase of the voltage, the LED current will increase as well. If having been working more than rated current job for a long time, the service life of the LED can greatly shorten. And the LED constant current is to ensure the working current constant in the environmental factors such as temperature and voltage changes.

2. How can the LED fluorescent lamp power supply be matched with lamp panel?

Some customers design lamp panel first, then find the power supply which is difficult to find, either the current is too big but the voltage is too small (such as I > 350 ma, V < 40 V); or the current is too small, voltage is too high (such as I < 40 ma, V > 180 V). The results are serious fever, low efficiency, or the input voltage range is not enough. In fact, choose one of the most excellent ways of connection and voltage current added on each LED is the same, where the effect of the power supply can play the best performance. The best way is to communicate with power supply manufacturer and then tailor the most suitable one.

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

Generally the rated working current of the LED is 20 milliampere, and some factories use them all from the start to design 20 milliampere. In fact this electrical work will result in serious heating, through the contrast test for many times, the ideal one is designed to 17~19 milliampere and the recommended design is 18 milliampere.

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

LED recommended working voltage is 3.0-3.5V, and after the test, most of them work in 3.125V, so the 3.125V-type is quite reasonable. The total voltage of M LEDs=3.125*M.

5. How wide should the serial-parallel and voltage of LED be?

To make the LED fluorescent lamp work in a wide range of input voltage (full voltage) AC85~265v, the LED lamp board series parallel way is very important. Because the power supply is not commonly isolated buck type power supply, the output voltage should not be over 72V, and the input voltage range can reach 85~265v. Parallel number should not be too much; otherwise the working current is too large, with serious heating phenomenon. The total current should not be more than 240 milliampere as well. Another solution is using L6561/7527 to push the voltage to 400V, and then step down, the equivalent of two switching power supply, cost is twice as expensive, which has no market.

6. What are the relation among LED serial-parallel, PFC power factor and wide voltage?

Currently on the market power PFC has three conditions: one is without special PFC circuit, the general PFC is around 0.65; one kind is with passive PFC circuit, with light board horse well prepared, PFC general at around 0.92; and with a is made of active 7527/6561 circuit, PFC can reach 0.99, but the cost of this solution more expensive than the second scheme. So the second solution is more adapted. For passive PFC circuit, which is also called valley type PFC circuit, the working voltage range is half the peak of the input voltage. If input is 180V, the peak is 180*1.414=254V, half the peak voltage is 127V, subtracting the step-down type differential pressure 30V, its maximum output is 90V, so the LED lamp bead series number is up to 28 series. To get bigger of the power factor, therefore, lamp bead series number cannot be too much; otherwise, it cannot reach the requirements of low voltage.