On Thu, 14 Jul 2016 15:50:43 -0400, Phil Hobbs wrote:

On 07/14/2016 01:12 PM, Cursitor Doom wrote:
On Thu, 14 Jul 2016 11:53:30 -0400, Phil Hobbs wrote:

Too small an output cap, or too low an ESR? Three terminal regulators
can oscillate. Try hanging 100 uF aluminum electro on the output and
see if it starts behaving better.

The datasheet says output caps are "optional" although I do always use
'em. The one I'd fitted was 1nF which seemed a bit small, so I subbed
it for a 100n but it's made no difference. 100uF seems HUGE! I might
try it,
though.


100nF is guaranteed to make a 317 oscillate. Microfarads, me lad,
microfarads.

I'll certainly give it a try first thing tomorrow, Phil. But I'm not
optimistic given this confident pronouncement which I quote from the
datasheet:

"Typically, no capacitors are needed unless the device
is situated more than 6 inches from the input filter
capacitors, in which case an input bypass is needed.
An optional output capacitor can be added to improve
transient response. The adjustment terminal can be
bypassed to achieve very high ripple rejection ratios
that are difficult to achieve with standard 3-terminal
regulators."

So the manufacturers don't seem to think it's of any great importance at
all. BTW, on the input side, the filter capacitor is less than one inch
from the the reg's Vin terminal.