[sdiy] Linear PSU options .. 7815/7915 vs LM317/LM337 vs 723 etc

[harrybissell]

karl dalen wrote:

> Besides the droop voltage of 78xx series is something people
> often oversees, and the droop caused by load or irregular
> loading can be devastating for a VCO regarding to tuning
> aspects, so way use a 78xx in a VCO if you can use the 317
> with way better performance at the same cost?

1)  This would be a classic case of a poorly designed VCO that
used the power supply voltage for a reference... not a precision
reference for a reference. If the engineer did not stabilize the
VCO against this kind of problem, they were either sloppy... or
the design did not warrant the extra effort (hey good enough is good
enough !)

2) With the majority of opamps, such a droop of supply would probably
not
even affect amplitude of the waveforms (unless you were running them
in clipping...) If you WERE clipping and needed accurate amplitude...
there
are better ways to do that also (or good enough was good enough)

3) In a commercial product... if you used a 317 / 337 with a trimmer...
the
customer might do more damamge with a small screwdriver than a 78xx,
warts
included :^P

4) Maybe you stock 78xx and don't need to use another part... higher
volumes 
and lower prices

5) If I want adjustable, I reach for 317 / 337... for fixed I go with
78xx.
I will even use the dirty trick of a diode in the ground pin to change
the
voltage if I need that  :^)

I just think the 78xx series gets too much badmouth... they are NOT that
bad.
No worse than (lets say) the 555 anyway...

I did get burned, badly... once with a 78xx... but that was a defective
manufacturer / lot problem. Not enough to make me predjudiced...

H^) harry