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Is there a place that I can get a hold of a table with common voltages by using standard resistors? (Sorry that this is poorly worded but I cant figure out how to say it better, so I will give an example)

For example, a website that has a table that says for 5 volts on a LM317 you can use the "standard" resistor values of x for R1 and y for R2; with x and y being common resistor values.

Reid
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    Why would you need a table when you have the formula from the datasheet? – W5VO Mar 30 '12 at 17:40
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    When you Google 'lm317 calculator' you get tons of (kinda useless) calculation-forms. – PetPaulsen Mar 30 '12 at 18:28
  • I wanted something more than a "random" guess at what standard input would yield a standard output. – Reid Mar 30 '12 at 18:50
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    This is silly, just do the math! – Olin Lathrop Mar 30 '12 at 19:03
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    Actually, this makes sense. It's easy to pick R1 at random, but finding a standard R2 that matches is a pain. Such a table saves a few minutes of randomly stabbing at combinations. In fact, the paged linked in the accepted answer was a huge time-saver when trying to work out multiple combinations for a range of voltages. – Polynomial Mar 30 '12 at 21:59
  • Why not pick a ridiculously small or large R1, if a pot is being used for R2? What are the pros/cons of very small/very large values for R1? – Michael Goldshteyn Jul 27 '15 at 16:28

2 Answers2

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This page lets you enter the desired voltage and then calculates optimal values for the resistors. You can choose the resistors' series. For instance, if you select the E12 series, it will find the best match with resistors from the E12 series. Obviously E96 series will give better matches.

enter image description here

Some examples, with E12 (10%) resistors:

  • 3.3V: 1k2 + 1k8 \$\rightarrow\$ 3% error
  • 5V: 270 Ω + 820 Ω \$\rightarrow\$ 2% error
  • 9V: 560 Ω + 3k3 \$\rightarrow\$ 2% error
  • 12V: 390 Ω + 3k3 \$\rightarrow\$ less than 1% error
  • 15V: 1k2 + 12k \$\rightarrow\$ 4% error
  • 24V: 560 Ω + 10k \$\rightarrow\$ less than 1% error

(the first resistor is R1)

For comparison, with E96 (1%) resistors, all of the following have less than 1% error:

  • 3.3V: 365 Ω + 590 Ω
  • 5V: 1k02 + 2k94
  • 9V: 71.5 Ω + 442 Ω
  • 12V: 392 Ω + 3k32
  • 15V: 590 Ω + 6k34
  • 24V: 1k24 + 21k5
zx485
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flup
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  • See http://meta.electronics.stackexchange.com/questions/2757/policy-on-answers-only-containing-a-link – PeterJ Dec 28 '13 at 12:56
  • @PeterJ I explain what it does. Many of those calculators have it backward: they take the resistor values as input, and give you a voltage. This one also gives you E-values. – flup Dec 28 '13 at 13:02
  • The problem is when "this page" goes dead it no longer becomes useful. I've removed my downvote but what would make it much more useful in the longer term is to maybe include a little table in your answer that shows some common values for say 3.3V, 5V, 9V, 12V etc so when/if that happens it's still useful. I've probably edited / flagged a hundred posts because of dead links so it's best to try and make them continue to be valuable even when the links no longer work. – PeterJ Dec 28 '13 at 13:10
  • @PeterJ Better like this? Thanks for your reply. – flup Dec 28 '13 at 13:24
  • Yes just got my upvote :) – PeterJ Dec 28 '13 at 13:26
  • @PeterJ: The other answer is also just a link. Happens all the time :( – Johan.A Dec 28 '13 at 14:33
  • @Johan.A, I agree, now flup's answer is much better it will stand the test of time and eventually the other will become obsolete and probably get deleted if the link dies. – PeterJ Dec 28 '13 at 14:58
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This page shows such a table for R1 or 150 to 470 and R2 of 68 to 3300.

Brian Carlton
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