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I'm working on a project that requires me to use 3V LEDs with a Lux rating of about 150 lm @ 300 mA. I'm working with my PCB vendor, and they recommended an LED with the specs I'm looking for.

However, I noticed that the simplified schematic in their datasheet shows two LEDs in parallel inside the semiconductor package. I understand that putting LEDs in parallel like this is bad practice due to varying Forward Voltage thresholds tolerance.

Is it OK to use these kinds of LEDs if they are within the same semiconductor package?

enter image description here

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    \$\begingroup\$ Please add the data sheet link. \$\endgroup\$ Commented Aug 14 at 18:28
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    \$\begingroup\$ Great question. As TonyM explains, its all about matching. Manufacturers will usually do extensive testing on various parameters and offer ‘binned’ devices - ones that fall into tight criteria eg brightness, color etc. ones that fall out of spec but are still perfectly operational get sold off at a cheaper price- these are probably what you get via random suppliers. Be sure your board assembler sources via legit channels if you require consistency. \$\endgroup\$ Commented Aug 15 at 3:36

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They will be selected for similar Vf. The temperature is also nearly matched, being on the same base. No problem.

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  • \$\begingroup\$ If they're from the same wafer, especially nearby dice on the same wafer, you might not even have to go through a selection process. \$\endgroup\$ Commented Aug 16 at 13:19
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    \$\begingroup\$ I'd be inclined to suspect they're plain loose die (well, not loose loose, as if in a bag, lol, but tray or something, say), and packaging is done separately from wafer dicing (I mean, rather than immediately following). Dice might be sorted for wavelength, luminance and voltage, as a standard process. This way it's also more feasible for a 3rd party to package parts like this. If white, the phosphor probably has to be applied after bonding and packaging, entailing another color quality and luminance sort, but binned blue dice would still help with that. \$\endgroup\$ Commented Aug 16 at 16:09
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When they are assembling the duals the dies will all be off the same wafer so well matched, compared to what you might buy with individual LEDs (though if they’re on tape they’ll probably be from the same wafer most of the time, but..)

Also there’s a resistive component to the I-V curve that doesn’t appear in the ideal diode equation that helps match the current in parallel LEDs when they are run close to maximum current. If one of those two LEDs is brighter at low current it probably doesn’t much matter because they are physically close to each other.

Finally they’re thermally coupled so one diode won’t get radically hotter than the other (thus reducing Vf and aggravating the problem).

So, it’s fine just follow the data sheet for this compound component- the manufacturer is guaranteeing the performance under the specified conditions.

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The LEDs will be matched by being on the same substrate. They are fine to use and the manufacturer has endorsed such operation.

On the oft-heard view that LEDs can never be put in parallel because of varying drops between the LEDs: that's patently not true. For a start, we're surrounded by goodness knows how many 100,000's of commercial LCDs with LED backlights, using two parallel strings of series LEDs with a single driver. I finished the backlight drivers electronics for yet another project using one recently. They will match their LEDs somewhat.

As another example, some years back I worked on an industrial cutting laser that used parallel banks of matched-but-separate series LEDs with 50 A running through it all. However, the optics designers required a completely even light source and got it from their parallel LED strings over the long life and temperature variances of the industrial machine.

It's become a bit of an electronics 'old wives tale' that parallel LEDs just can't produce even lighting. It comes up on sites like this every so often, with apparently little knowledge of the actual market. And typed on a phone or laptop with a screen using that very parallel LED backlighting.

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