LM317 Load Regulation and Line Resistance

[MrFish]

Hi all, searched, but could not find an answer, so here goes:

The 317 datasheet (http://www.ti.com/lit/ds/symlink/lm117.pdf) has a section (bottom of page 10) on Load Regulation and the problem of line resistance caused, and/or exacerbated, by the distance of the current set resistor from the output pin of the regulator.

Load Regulation
The LM117 is capable of providing extremely good load regulation but a few precautions are needed to obtain
maximum performance. The current set resistor connected between the adjustment terminal and the output
terminal (usually 240Ω) should be tied directly to the output (case) of the regulator rather than near the load. This
eliminates line drops from appearing effectively in series with the reference and degrading regulation. For
example, a 15V regulator with 0.05Ω resistance between the regulator and load will have a load regulation due to
line resistance of 0.05Ω × IL
. If the set resistor is connected near the load the effective line resistance will be
0.05Ω (1 + R2/R1) or in this case, 11.5 times worse.

I believe that I get the idea, at least the general guideline to internalize when laying out a board (keep the current set resistor as close as possible to output terminal), and the formula for determining the resistance.  However, could anyone take a crack at unpacking that datasheet note a bit more? 

More precisely, let's say we're laying out a PCB of a pedal power supply like this:

12v regulator (317 in a TO-220 package with 240Ω and 2.2k) with the output(s) coming off the board [to DC jack(s) on the enclosure].

Is this datasheet note aimed at higher demand "commercial" applications?  What are the distances they're actually talking about?  (I might have missed it, but I didn't see an example of a length referent vis a vis this note, so I'm not sure how to implement its warning (other than, as I mentioned, just try to keep the resistor as close as possible to the output terminal).

Any guidance would be appreciated, perhaps a thread I missed?  Thanks!

[armdnrdy]

A "load" of examples available here:

https://www.google.com/search?q=LM317+power+supply+circuit+board&rlz=1T4GGHP_enUS450US450&source=lnms&tbm=isch&sa=X&ei=SQExU8KMIs7aoATr_oJA&ved=0CAgQ_AUoAQ&biw=1024&bih=662

[PRR]

This is to power pedals?

Don't put R1 a yard (meter) away from the chip. Don't use wet spaghetti as jumper-wire.

In any sane layout R1 will be within an inch of the chip, their "Rs" will be negligible, especially for pedal-loads, which are not (should not be) super-sensitive to teeny voltage variation.

Yes, that note covers their butt if you attempt HIGH current HIGh precision regulators. The '317 acts different from LM300-types so the precision designer needs to detail it different. But billions of working products pay no attention to that note without ill effect.

[MrFish]

haha,

Yeah, I kinda figured it was probably a note aimed at "commercial" or higher demand applications, especially since I'd never heard anyone talk about it before...

Thanks for the response, cheers!