[geeks] Voltage regulators don't!

[der Mouse]

Grrr.  Rant alert.

I was trying to build a 13.71.1 volt supply, and wanted it to be at
least vaguely regulated.

So I got out my 7805s, thinking to use the construction where ground on
the 7805 is connected to a voltage divider between the output and the
"real" ground.

And...I find that about 2/3 of them simply don't work.  After trouble
with the construction I mentioned, I started using them as simple 5V
regulators.  I was feeding them about 23V, coming from a transformer, a
bridge rectifier, and a serious filter cap (0.03 farad).  The "broken"
ones all produce a very nice 5V under no load, but when I give them a
1Kohm load (ie, all of about 5 milliamps of draw) the output voltage
plummets to under 4V.  150 ohms of load and it drops to about 1.02V.
(It's not supply problems, either.  Under the 150 ohm load, the input
supply sags - to some 18-19 V - but has only about 65mV of ripple; that
30000uF filter cap does its job well.)

Fortunately, there were about four that did work (output voltage
changes by maybe as much as 0.02V even under the 150 ohm load).  But
I'm still pretty annoyed, because most of the "broken" ones were brand
new from Digikey - and, I think, all of the new ones are broken.  (If
I'd kept careful track of which ones were new, I'd call up Digikey and
get upset about it, but I just dumped them into the drawer with the
others.)

There is some slight chance the problem is oxide on the leads, because
I was using alligator clip leads to connect to them.  I'll try
soldering wires onto one and see if that helps.  But still...grrr.

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