Re: gEDA-user: Dropping a few volts

[Randall Nortman <geda-lists@xxxxxxxxxxxxxxx>]

On Fri, Oct 12, 2007 at 09:46:16AM -0400, John Luciani wrote:
> There may be a TL431 application circuit that could be work. Check out
> the TL431 datasheet from TI.

Well, I think you've fixed my problem, but it doesn't involve the
TL431.  But the datasheet inspired me -- I see them using it to
control a 7805 three-terminal regulator, which is an interesting idea.
(Figure 20 in TI's version of the datasheet at
http://www.ti.com/lit/gpn/tl431).  The TL432 effectively raises the
ground reference of the 7805 to Vout-5V.  This would work in my
application, as the 7805 would only see Vin-Vout+5V instead of the
full 42V, and so it would be operating within its limits.  But this
basic circuit layout looks suspiciously to me like a basic
three-terminal adjustable regulator, using GND in place of the ADJ
terminal and the TL431 to provide the reference for that terminal.

So why not use a standard-issue three-terminal adjustable regulator
circuit?  Those things don't care what Vin is, only Vin-Vout.

Duh!

Thanks for the help, even if you didn't realize what answer you were
really giving.  ;)

-- 
Randall


_______________________________________________
geda-user mailing list
geda-user@xxxxxxxxxxxxxx
http://www.seul.org/cgi-bin/mailman/listinfo/geda-user