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Why do electronic components have such odd values? (2021)

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Re: Why do electronic components have such odd values? (2021)

#111

Post by [deleted] »

SamBam wrote: post #110
throw0101d wrote: post #34

This part is the thing that made me understand the numbering series: > […] Continuing this trend, rounding as needed, and we end up with the series 10, 15, 22, 33, 47, and 68. Components built to the E6 standard have a 20% relative error tolerance, and if we look at the values again we’ll see a trend. Starting with 10 again and adding 20% error we end up with 12. Moving to 15 and subtracting 20% we get… wait for it……

I still don't really get the overlapping tolerances, though, because each resistor is not a range, it's a single value that's somewhere in that tolerance. He says about the cables: > Each size of cable had a max/min rating that just overlapped it’s neighbor above and below, so every required value was covered by one or more cable. So that means if you needed a "size 12" cable you could pick a size 10 OR a size 15, an…

[deleted]

Re: Why do electronic components have such odd values? (2021)

#112

Post by SAI_Peregrinus »

SamBam wrote: post #110
throw0101d wrote: post #34

This part is the thing that made me understand the numbering series: > […] Continuing this trend, rounding as needed, and we end up with the series 10, 15, 22, 33, 47, and 68. Components built to the E6 standard have a 20% relative error tolerance, and if we look at the values again we’ll see a trend. Starting with 10 again and adding 20% error we end up with 12. Moving to 15 and subtracting 20% we get… wait for it……

I still don't really get the overlapping tolerances, though, because each resistor is not a range, it's a single value that's somewhere in that tolerance. He says about the cables: > Each size of cable had a max/min rating that just overlapped it’s neighbor above and below, so every required value was covered by one or more cable. So that means if you needed a "size 12" cable you could pick a size 10 OR a size 15, an…

Each resistor in the design is a range. The designer picks the tolerance to use, some resistors will be fine with a 10% tolerance, others only with a 2% or 1% tolerance.

Also each resistor is a range, not a single value, since each resistor changes value with temperature & other environmental factors (though temperature is the biggest). That variation is (for normal resistors) less than the tolerance range.

Re: Why do electronic components have such odd values? (2021)

#113

Post by mastax »

LeifCarrotson wrote: post #90
bsder wrote: post #88

Earlier quoted context omitted.

Mostly, no. Nobody except for expensive precision resistor companies are actually measuring resistors more than statistically. The resistors are manufactured so that they are "guaranteed by manufacturing" such that the outliers are 1%, 5%, 10%, etc. And they do statistical checks on batches, but not really looking for the 10% outlier (which is stupendously rare and very difficult to catch) but looking for slight drif…

Is this how LEDs are binned as well, or are they powering each node on the wafer before packaging? They're orders of magnitude more expensive than resistors, so I figure they might... There are all kinds of crazy parameter variations in optoelectronics. I understand that resistors are really close to nominal because the manufacturer's ability to tune the process controls are so much better than the standard 5% and 10…

I saw a video from the WS2812 factory and from what I remember all of the LEDs were tested individually on the die before assembly. I don’t know if that’s typical but those are pretty cheap for what they are.

Re: Why do electronic components have such odd values? (2021)

#114

Post by SAI_Peregrinus »

rchowe wrote: post #78
xw390112 wrote: post #66

Earlier quoted context omitted.

In 2024, if your resistor vendor has even 5% tolerance, you need to find another vendor.

Thin-film resistor design engineer here! It's dependent on value and geometry -- if you order a 0.5 ohm resistor the meters on our trimming lasers only go down to 20 mΩ and you're getting a 5% part at best.

And that's why the really precise resistors are so damn expensive. E.g. VPG makes a 10k 1/5W 0.001% tolerance ±0.2ppm/°C, but they're $116 each with a minimum order quantity of 25 on DigiKey (so $2900 minimum purchase). They've got a really expensive meter for their trimming setup!

Re: Why do electronic components have such odd values? (2021)

#115

Post by KennyBlanken »

alright2565 wrote: post #98
rchowe wrote: post #78

Earlier quoted context omitted.

Thin-film resistor design engineer here! It's dependent on value and geometry -- if you order a 0.5 ohm resistor the meters on our trimming lasers only go down to 20 mΩ and you're getting a 5% part at best.

What about shunt resistors? I can pretty easily get a 1% 5mΩ resistor, but they don't look to me like they are constructed in the same way as a generic resistor.

They're made in a bunch of ways but the general principle is "the stuff inside is much lower resistance than what's normally used."

Re: Why do electronic components have such odd values? (2021)

#116

Post by klodolph »

Brian_K_White wrote: post #100
joemi wrote: post #57

Earlier quoted context omitted.

How do the tolerances combine when you're using two resistors? I'm pretty sure they'd add together if in series (so two 5%'s become 10%), but I'm having trouble easily intuiting what happens if in parallel. Do they combine in the same way that resistances combine when in parallel? edit: Actually, I'm not so sure anymore that the tolerances would add up in series... I should probably just look this stuff up, since I'm…

Values (for resistors) add in series and sort of divide-average in parallel. In either case though, the tolerance divides. The combined tolerance becomes more accurate the more resistors there are in total, whether parallel or serial. The highs and lows, and the chances of high or low, cancel each other out and you get a final actual value that is closer to the nominal statistical center of the bell curve the more in…

> or less, I bet the actual equation is more complicated

https://en.wikipedia.org/wiki/Central_limit_theorem

I’m a bit tired otherwise I’d write something more rigorous. There are different ways the central limit theorem is expressed and proved here—there are more powerful ways to state it that require more complicated proofs, and there are simpler versions that are simple to prove.

A simple version will suffice here. Treat the resistors as iid variables with finite variance σ². When you average them, the variance of the average is σ²/n. More or less… this means that if your resistors are ±10%, and you have 16 of them, you get something with (fuzzy math) ±10%/√16 = ±2.5%.

There’s a lot of unstated assumptions in what I just wrote. But you’ll see the “grows proportional to √n” a lot in stats.

Re: Why do electronic components have such odd values? (2021)

#117

Post by klodolph »

londons_explore wrote: post #84
klodolph wrote: post #44

Earlier quoted context omitted.

Yes—although E96 is cheap, I’m still very fond of E12. You get to keep less stock. I’ll even use two resistors rather than use something outside E12, most of the time. Maybe it’s habit? Hell, I don’t even think all of E12 is necessary. I’ll stick to E6 most of the time.

Being a mostly-digital electronics guy, I think 0.1, 1, 10, 100, 1k, 10k, 100k, 1M and 10M is a perfectly fine series for pretty much any usecase. Sense resistor? 0.1 ohm. Resistor for an LED: 100 ohm Pull up resistor: 10k Bias resistor for some mosfet gate: 10M Voltage divider to measure the battery voltage with an ADC: two 100k resistors. It's super rare I need anything else. I hate fiddling about with switching th…

I do mostly analog and being off by a factor of 2 or 3 is gonna ruin your day.

Re: Why do electronic components have such odd values? (2021)

#118

Post by pavon »

joemi wrote: post #57
klodolph wrote: post #44

Earlier quoted context omitted.

Yes—although E96 is cheap, I’m still very fond of E12. You get to keep less stock. I’ll even use two resistors rather than use something outside E12, most of the time. Maybe it’s habit? Hell, I don’t even think all of E12 is necessary. I’ll stick to E6 most of the time.

How do the tolerances combine when you're using two resistors? I'm pretty sure they'd add together if in series (so two 5%'s become 10%), but I'm having trouble easily intuiting what happens if in parallel. Do they combine in the same way that resistances combine when in parallel? edit: Actually, I'm not so sure anymore that the tolerances would add up in series... I should probably just look this stuff up, since I'm…

If the resistor values are distributed as a Gaussian where the tolerance is some confidence interval, then the total resistance of resisters in series would be distributed as the sum of those Gaussians whose tolerance would be the root-sum-square of the individual tolerances: sqrt(tol1^2 + tol2^2 + ... tolN^2), or if all the tolerances are the same then sqrt(N)*tol.

Re: Why do electronic components have such odd values? (2021)

#119

Post by eternityforest »

nick238 wrote: post #59
eternityforest wrote: post #43

Earlier quoted context omitted.

I'd say if you need more than E3, you either know a lot of not much, unless you're into analog. I've done stuff that needs high precision resistors, but usually the specific value isn't that important, just that it's a known repeatable value.

If I want a voltage divider, it's a lot easier to just use some 1% resistors and forward-calculate the expected output (rather than doing a calibration) if you're happy with 1-2% error from the resistors and your ADC or the like. Adding software and testing hardware to do a full on calibration is a lot of work. But yeah, for digital signals, oft times 1k or 100k make no difference.

I definitely agree that 1% or better resistors are easier than calibration, but that doesn't mean you need values outside of E3 most of the time.

I might want want an accurate 1/10 divider or something, but a 1/12 divider would probably be fine too, as long as it's consistent. If it doesn't vary between devices, it's just a line of code to change.

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