[sdiy] Negative voltage references

David G Dixon dixon at mail.ubc.ca
Sun May 20 03:34:16 CEST 2012

I use 79L05 all the time for -5V regulation, particularly with linearized
2164 VCA circuits.  It works great.  Those will source up to 100 mA (but
they do get pretty warm at that current).  I only use bandgap references in
VCO circuits.  I've never used the big 7905s (the ones with the big hunk of
metal on the side) so I can't comment on those.  The 79L05 comes in a TO-92

What's it for, anyway?

> >> Ideally, anything you hang off it will need to be via an op amp 
> >> buffer.
> > 
> > That's really important.  One must take a close look at the current 
> > specs for whatever is used.  LM4040 is pretty low.  REF02 is better.
> > 
> > For me personally, the best practice is to buffer and invert any 
> > reference voltage with a dual opamp, and then you can use 
> any single 
> > positive reference and you don't have to worry about it.
> Ok, so the advantage of the "cheap regulator" over the 
> "expensive reference" would be that you don't need any 
> buffer, since a voltage regulator can provide as much current 
> as you're likely to need. After all, you could easily spec 
> the regulator for 1A or more. The disadvantage is that the 
> regulation isn't that good, especially if the load is low. 
> I've got a L7905CV on my breadboard which is supposed to be 
> producing -5V and is actually producing -6.8V. I expect it 
> would improve a great deal if I stuck an LED across it, but 
> it seems a bit crazy. I wanted to use a 79L05 but didn't have 
> one to hand, so used the "next nearest".
> Hence the original question about negative voltage references.

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