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| LED Lighting (350 mA). Is there any standard for # of LEDs is a string? |
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| Zero999:
--- Quote from: Benta on August 13, 2022, 07:00:22 pm --- --- Quote from: Zero999 on August 13, 2022, 09:31:13 am ---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. --- End quote --- I have an engineering rule that I always stick to: never do a basic design based on probabilities, typical values or wishful thinking. You can always downgrade afterwards based on experience. And thinking that a reel of parts exhibit a nice Gaussian distribution is wishful thinking. You never know if a really big customer has asked the manufacturer to select parts with a certain. VF. This happens much more often than you think (don't ask me how I know, I've been in the semiconductor industry for 40+ years). The rest is sold on the open market, but the Gaussian distribution is gone, although all parts confirm to specs. --- End quote --- That's exactly why I keep saying do some actual measurements, before finalising the design. |
| Benta:
And why I'm saying do worst-case/best-case or minimum/maximum spec analysis first. Measurements will not cure the "wishful thinking" part. Calculations will. |
| nctnico:
--- Quote from: Benta on August 13, 2022, 07:04:22 pm --- --- Quote from: nctnico on August 13, 2022, 06:30:59 pm --- --- Quote from: T3sl4co1l on August 13, 2022, 03:56:54 pm ---I don't mind running at ratings, personally; as long as they're good parts, that's what really matters. That, and thermal management. --- End quote --- Thermal management is easy to underestimate. Even 60mW LEDs need like 4x4mm pads in order to have sufficient heatsinking in real life applications. --- End quote --- Very true, but in this case quite easy: total PD is 19 x 0.35 A = 6.65 W. Not insurmountable. The idea is to mount the lights/LEDs/regulator on an aluminium baseplate anyway. Shape TBD. --- End quote --- To be sure: I'm writing about 60 milli-Watt = 0.06W! |
| Benta:
--- Quote from: nctnico on August 13, 2022, 08:45:14 pm ---To be sure: I'm writing about 60 milli-Watt = 0.06W! --- End quote --- I understand fully what you're writing. But I've designed 150 W Class-AB amps and 20 W Class-A amps. Thermal management of 6.7 W is easy. You keep on harping on this. Why? A standard 0.3 W resistor won't even get a little warm at 0.06 W. |
| Zero999:
--- Quote from: Benta on August 13, 2022, 07:20:07 pm ---And why I'm saying do worst-case/best-case or minimum/maximum spec analysis first. Measurements will not cure the "wishful thinking" part. Calculations will. --- End quote --- Calculations putting the worst case into everything will often result in over-engineering, which might be acceptable in safety critical applications, but otherwise counterproductive. |
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