Voltage regulator

[neo]

What happens if the adjust pin gets positive voltage? lm338k

[Andy Watson]

Positive ?

With respect to what ?

[Cliff Matthews]

PLS name part number in question...

[neo]

lm338k i think i might have fried it testing it, test circuit below, positive with respect to ground. I would like to note this is to-3 package so me acidently confusing pin 1 and 2 is nowhere near as dumb as it sounds

[Cliff Matthews]

Drawing's a bit up-side-down, but this layout for current limiting. Did you see any smoke?
It will try to maintain 1.25v across R1 and if R1 was a low enough value, you may have fried that pot.

[neo]

no smoke but it is hermetically sealed steel after all, and that should be a voltage regulating circuit ive used it before r1 was a hundred ohms

[Cliff Matthews]

Hook it up as a standard regulator to a 12v low current wall-wart and see what you get.
Also Google "lm338k fakes", since lots of these are fakes from China. 

[neo]

mine are old made in america ones, or were perhaps i broke them. How do you suggest hooking it up i took that straight from the datasheet http://www.st.com/content/ccc/resource/technical/document/datasheet/group1/07/c7/47/cb/15/f7/4b/ec/CD00000548/files/CD00000548.pdf/jcr:content/translations/en.CD00000548.pdf

[Cliff Matthews]

It's a PITA to break those.. in my local, these are $10 each. Keep it simple, 12vdc in, R1=240, R2=1K and you should get ~6v out.

[neo]

well i feel like an idiot but im going to say it anyway as a message for the new players reading this, NOTHING is infallible if it works when you test it 5 times but doesnt in circuit test it in circuit, the voltage regulator wasnt working because the second current was applied the resistor, previously infallible, failed i changed that pot for a different one and the problem is instantly solved. Though in all fairness i started this thread for ideas as much as i did out of annoyance (when i posted i had just finished two hours of being teased by that pot)