2
\$\begingroup\$

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.

\$\endgroup\$
6
  • 6
    \$\begingroup\$ Why would you need a table when you have the formula from the datasheet? \$\endgroup\$
    – W5VO
    Mar 30, 2012 at 17:40
  • 2
    \$\begingroup\$ When you Google 'lm317 calculator' you get tons of (kinda useless) calculation-forms. \$\endgroup\$
    – PetPaulsen
    Mar 30, 2012 at 18:28
  • \$\begingroup\$ I wanted something more than a "random" guess at what standard input would yield a standard output. \$\endgroup\$
    – Reid
    Mar 30, 2012 at 18:50
  • 3
    \$\begingroup\$ This is silly, just do the math! \$\endgroup\$
    – Olin Lathrop
    Mar 30, 2012 at 19:03
  • 3
    \$\begingroup\$ 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. \$\endgroup\$
    – Polynomial
    Mar 30, 2012 at 21:59

2 Answers 2

Reset to default
10
\$\begingroup\$

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
\$\endgroup\$
7
  • \$\begingroup\$ See meta.electronics.stackexchange.com/questions/2757/… \$\endgroup\$
    – PeterJ
    Dec 28, 2013 at 12:56
  • \$\begingroup\$ @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. \$\endgroup\$
    – flup
    Dec 28, 2013 at 13:02
  • \$\begingroup\$ 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. \$\endgroup\$
    – PeterJ
    Dec 28, 2013 at 13:10
  • \$\begingroup\$ @PeterJ Better like this? Thanks for your reply. \$\endgroup\$
    – flup
    Dec 28, 2013 at 13:24
  • \$\begingroup\$ Yes just got my upvote :) \$\endgroup\$
    – PeterJ
    Dec 28, 2013 at 13:26
3
\$\begingroup\$

This page shows such a table for R1 or 150 to 470 and R2 of 68 to 3300.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.