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Designing an efficient LED array (discuss.tchncs.de)

submitted 7 months ago by [email protected] to c/[email protected]

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LEDs will conduct more current when they get warmer and differences between individual LEDs mean you cannot easily put them in parallel. A constant current DC supply will be good enough for part of the LEDs but will overload some others. To normalize current a series resistor is used with each individual LED.

Now, those resistors waste a bit of power. Are they really necessary? If you put several LEDs in series the individual differences become negligible at some point and a constant current supply will suffice for several strips of series LEDs in parallel.

How many LEDs would this require? Another possibility would be to have the resistor in series with a strip of LEDs.

I got some LED strips off AliExpress that run on 12V and each individual LED has a resistor in series with it. I believe this to be quite wasteful and it would be better to have several LEDs in series with a current regulator instead. The LEDs will end up in an autonomous greenhouse where power efficiency is important.

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[–] [email protected] 6 points 7 months ago

You need to control the current going through the LED, either by wasting it as heat (resistor or linear controller) or via switching power supply mechanisms.

Non-intelligent LED strips (where the whole strip is the same color, as opposed to the intelligent kind where each LED can be a different color) are generally not using a resistor per LED because you can use a row of LEDs in series with a single resistor. Generally there's a marking to designate where you can cut such that they've got several LEDs per resistor because each LED is going to be somewhere in the 2-3V range, depending on color.

Strips are a design compromise built around convenience, of course. But there's a lot of engineering compromises here because the switching power supply is going to burn up some energy running things as well.

Manufacturers of finished LED products do make bright LEDs frequently by making a series-parallel array of LED chips on a single substrate such that they've pre-selected similar LEDs. But if you are building your own strips, you can use a constant-current switching supply to run a series of LEDs off of a relatively high voltage, somewhere in the 24v to 48v range, where you'd want to select for a relatively bright individual LED so you don't need to make a bunch of the constant-current switching power supplies.