[sdiy] 7915 regulators

[Jaco Sloof NewbieSynthBuilder]

--- Seb Francis <seb at is-uk.com> wrote:
> Jay Schwichtenberg wrote:
> 
> > In my experience the pin outs are the same for the same type. But
> the pin
> > outs are different between the 78XX/79XX. Check that out.
> 
> Yep, and more annoyingly the metal tab is not connected to ground
> on the 79XX, so you have to insulate-mount to share the same
> heatsink with 78XX.
> 
> > Yes put a small
> > load on them for testing. Some will work others won't without a
> load. Also
> > with 30 volts in put a big heat sink on it or a small (in
> resistance, not
> > current) power resistor in series to dissipate some of the power
> going into
> > the regulator.
> 
> The transformer is rated 20VAC 1Amp, so I'm assuming the voltage
> across the smoothing cap will drop under load.  There's a 15VAC tap
> on the transformer, but I figured this might be too low under full
> load.  In any case, this is only a bench power supply for powering
> my breadboard, etc.. so the duty cycle should be quite low.
> 
> >
> > I read a lot on 78XX/79XX regulators and gave up using them on
> anything that
> > is remotely serious. There was an article on power supplies for
> audiophiles
> > in Audio Amateur by Walt Jung and Jan Didden (sp?) that made me
> give up on
> > them. Basically it said the 78/79 were junk, LM317/LM337 were
> better and
> > LT1086/LT1175 were tolerable in audio. They were looking at
> ripple rejection
> > and noise. Each set was about -10 db quieter than the others.
> Anymore I use
> > LM317/LM337 for misc things and the Linear Tech parts for audio.
> 
> I tend to agree with you (going by what I have read).  In my
> modular PSU I'm using LM723s with power transistors to get the
> current.  I did try measuring the noise amplitude of the 7815 vs
> LM723 with a digital scope, and actually it seemed pretty similar
> .. but I think it was right on the edge of the scope's resolution
> at that voltage offset.  My cheap+easy 3 rail bench-PSU based on
> 7XXX seems ok though .. now that I know I have to put a bit of load
> across the 79XX to get the right voltage.
> 
> Cheers,
> Seb
> 
> 

I must agree too, i had a lot of trouble getting 78/9xx regulators to
work, so i gave them up all together, some listmembers might remember
my tediously irritating questions about them...

No i just use 317 337 design, works like a charm... and yes, these
also need a "linearising"-resistance on the output... mine was the
leds with a 2K resistor. 

Greets, Jaco Sloof
http://synthsite.8m.com
(i promise to make some updates this week)

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