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LED Lighting (350 mA). Is there any standard for # of LEDs is a string?

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deadlylover:
Which LEDs are you using? Were they the OSLON square on eBay binned below the BBL? (like this 3500k) Those are an excellent choice.

I've always wanted to try them but I have been a Nichia fan lately. (it helps that Cutter Electronics in Australia is kinda local to me, so I just use their strips for DIY projects)

A while back I upgraded my room/desk lighting using the Nichia Optisolis 757 series. Museum grade lighting because I'm a bit of a colour pencil hobbyist too.  :P

Benta:

--- Quote from: Zero999 on August 12, 2022, 05:29:34 pm ---Here's what I was talking about earlier. It requires just under 1V of headroom.

--- End quote ---
OK, so right now I have three resistors,* a BD437 and a TLV431. (*) Ok one is actually three to hit the value and spread power.
And now I need the same PLUS an LM358 (plus an additional dropper resistor for the reference). Not really a simplification to my mind.

Zero999:

--- Quote from: Benta on August 12, 2022, 07:58:04 pm ---
--- Quote from: Zero999 on August 12, 2022, 05:29:34 pm ---Here's what I was talking about earlier. It requires just under 1V of headroom.

--- End quote ---
OK, so right now I have three resistors,* a BD437 and a TLV431. (*) Ok one is actually three to hit the value and spread power.
And now I need the same PLUS an LM358 (plus an additional dropper resistor for the reference). Not really a simplification to my mind.

--- End quote ---
It wasn't supposed to be simpler, but more efficient. Now the transistor can be cheaper and doesn't even need a heatsink. A cheaper TL431 can also be used if the values of R2 & R2 are changed to 160k & 12k.

It depends on how many strings of LEDs you want per luminaire. If you want to use two or more strings, then my circuit requires fewer components. For another string all that's needed is an extra transistor and current sense resistor, then there's the LM324, if you need three or four strings.

Benta:

--- Quote from: Zero999 on August 12, 2022, 08:13:00 pm ---It wasn't supposed to be simpler, but more efficient. Now the transistor can be cheaper and doesn't even need a heatsink. A cheaper TL431 can also be used if the values of R2 & R2 are changed to 160k & 12k.

It depends on how many strings of LEDs you want per luminaire. If you want to use two or more strings, then my circuit requires fewer components. For another string all that's needed is an extra transistor and current sense resistor, then there's the LM324, if you need three or four strings.

--- End quote ---
In a perfect world, yes. But (just as an example) the OSLON voltage binning (K2...M2) spans 2.75...3.2 V. So the BC337 will either run nice and cool or be in flames, depending on LED bin availability.

Second, and I've said this before: the idea is to have the 4/5/6-LED strings running autonomously at 19 V for free placement.

Zero999:

--- Quote from: Benta on August 12, 2022, 09:37:52 pm ---
--- Quote from: Zero999 on August 12, 2022, 08:13:00 pm ---It wasn't supposed to be simpler, but more efficient. Now the transistor can be cheaper and doesn't even need a heatsink. A cheaper TL431 can also be used if the values of R2 & R2 are changed to 160k & 12k.

It depends on how many strings of LEDs you want per luminaire. If you want to use two or more strings, then my circuit requires fewer components. For another string all that's needed is an extra transistor and current sense resistor, then there's the LM324, if you need three or four strings.

--- End quote ---
In a perfect world, yes. But (just as an example) the OSLON voltage binning (K2...M2) spans 2.75...3.2 V. So the BC337 will either run nice and cool or be in flames, depending on LED bin availability.

Second, and I've said this before: the idea is to have the 4/5/6-LED strings running autonomously at 19 V for free placement.

--- End quote ---
You have many LEDs in series, so the variation in forward voltage drops will cancel each other out. You won't have six 2.75V LEDs, or 3.2V LEDs, but an even distribution of forward voltages, giving a total forward voltage of about 3V.

As I said before, you should get hold of the real components and measure the voltages at different currents. It's probably also a good idea to breadboard it before finalising the circuit.

I strongly recommend running the LEDs at less than their ratings. It doesn't reduce the brightness much, but greatly increases the efficiency and lifetime.

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