Electronic – Why LED street lamp can parallel LED without damage

led

I working on DC LED street light driver using this LED street light look like picture bwelow.
enter image description here

I don't know much about this LED but it use about 30V to drive and I design CC drive for it.
The white LED usually got Vf about 3V. My lamp got 90 LEDs on it, so I assumed the schematic look like this (10 LED in series x9 in parallel). Why we can use LEDs in parallel in this situation?
I remembered we should not parallel the LEDs.

  1. Vf of LEDs can be difference.
  2. Temperature make VI curve changed.

Note: This schematic is just my assumption. If you has real schematic please share.

schematic

simulate this circuit – Schematic created using CircuitLab

Best Answer

Here's an excerpt from some Yuji LED datasheet:

enter image description here

So yes, if you order in quantity you can get LEDs with good Vf match. Wiring them in series strings means the Vf mismatches add and substract which increases the probability that total Vf will be closer to (number of LEDs x average Vf).

If they are mounted on an aluminium PCB which keeps them all at the same temperature, Vf under load will track pretty well. This means they can be arranged in series/parallel strings without resistors or other current sharing/limiting devices. This is very common in LED lights.

If the LEDs are not binned by Vf, and especially if they are at different temperatures, then it wouldn't be a good idea to parallel them.

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