LED lamp driver power matching solution

Now let's take an 18" LED tube as an example to analyze the design ideas:

Let's take the most commonly used 3528 lamp beads as an example. When LED lamp tubes first came out, due to the large price gap, light strip manufacturers all used LED chips with high current consistency and high brightness. The current of this type of chip is generally: 20mA;

First, calculate the power of a lamp bead: 3528 A lamp bead consists of 1 chip, voltage: 3.2V; (parallel circuit: voltage remains unchanged, total current is added) If it is a good quality LED chip: the current of a single chip is 0.02A, then the power of a lamp bead is 0.02A×3=0.06W. However, in the actual design of the LED chip on the market: the current of a single chip is designed to be 0.018A (considering the margin), then the power of a lamp bead is 0.018A×3.2v=0.0576w.

Second, we must first consider whether the lamp is isolated or non-isolated. Power W = voltage V × current A, so we can first roughly estimate how many beads are needed: 18/0.0576=312.5, about 312 beads

Third, we assume that it is isolated, and the general voltage should be less than 36v, that is, 36/3=12 strings. Non-isolated ones are generally set to 24 strings. 312/12=26 parallel; 312/24=13 parallel. In this way, we can preliminarily determine two solutions: 12 strings and 26 parallel isolation and 24 strings and 13 non-isolated. Fourth, we can choose the driving solution based on this: First, for this kind of engineer, you can communicate directly with the driver factory, ask them to adjust the input power to 18w, and tell them your lamp bead string and parallel method. If you are facing sales, you can tell you that the current and voltage of the LED driver output are as follows: Isolated solution: voltage V=36vI=0.18*26=470MA Non-isolated solution: voltage V=72vI=0.18*13=235MA

Fifth, it is worth noting that the above is an ideal design, but in reality we often have to consider a lot when designing, such as cost. First of all, the number of our lamp beads is 312, and the power of the lamp board is already 18w, so the power of the lamp must be greater than 18w. So at this time, we have to consider the efficiency and pf value of the driver: if the power of the power supply is 18w, the pf value is 0.95 and the efficiency is 0.85, then we will design the pcb board according to the power supply.

The method is as follows: the power of the light board = 18*0.85 = 15.3w, the number of equal numbers = 15.3w/0.0576 = 265.6 is about 266, but considering 12 strings, we set the number of lamp beads to 264. This is another two solutions: 12 strings and 22 parallels and 24 strings and 11 parallels. Of course, it can also be 11 strings and 24 parallels and 22 strings and 12 parallels. As long as the isolated voltage is less than 36v, it will be fine. This is also a reverse design idea. Generally, the two are combined.

After completing the above LED power supply matching design work, you can design the power supply circuit board according to product requirements.