On Thu, 14 Jul 2016 18:47:03 -0000 (UTC), Cursitor Doom
wrote:
On Thu, 14 Jul 2016 10:35:32 -0700, Jeff Liebermann wrote:
Maybe you blew up the
LM317?
Don't see how that's possible, Jeff, since it's still happy to supply
passive loads that are much heavier, and at a rock solid stable output
voltage.
I can't argue with that, except that several people and the data sheet
have mentioned that the LM317T doesn't like light loads and has a
minimum load current specification. Since this is your problem, not
mine, I can only offer suggestions and things to try. Since your
regulator doesn't like a light load, kindly put a load resistor across
the 12V line and see if the situation improves. (Hint: When
troubleshooting, I like to do easy things first. A resistor is easy).
Incidentally, it is possible to damage an IC to the point where it
still functions, but no in the manner commonly expected. I've done
this numerous times with RF power transistors, where there are a bunch
of transistor in parallel inside the packages. The LM317T probably
doesn't have this exact problem, but might not appreciate having some
holes blown in the IC's insulating layers. It's not easy to test for
this, so just replace the LM317T with one that has a good chance of
working.
I'm also wondering if there's something odd about your construction
methods. I've seen 3 terminal regulators work well on a PCB
breadboard with good grounding, and then go nuts when laid out on a
PCB, where the ground follows a long and twisted path to the
regulator. A big electrolytic on the output helps, but only if the
leads and traces are fairly short. If you built your regulator on one
of those solderless breadboard abominations,
https://www.google.com/search?q=solderless+breadboard&tbm=isch
then I suggest you find a piece of PCB material and build it better.
Then give the solderless breadboard to your worst enemy.
As for the 555, it allegedly draws very little current, but it doesn't
hurt to check. Insert a 1 ohm resistor in the PS line and measure the
drain with a differential input scope (i.e. using 2 scope probes).
Look for giant current spikes and high freq oscillations, that don't
belong.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558