opamp rescaling..

Scott Gravenhorst chordman at flash.net
Sat Nov 13 10:14:51 CET 1999


I've done this using a "virtual ground"

I've used this sort of thing:


     * +5 volts
     |
     |
     |
     >
     >    +--------------+
  R  >    |              |
     >    |   |\         |
     |    |   | \        |
     |    |   |  \       |
     +----+---+ - \      |
     |        |    \     |
     |        |     >----+----------+
     |        |    /                |
     >    +---+ + /                 |
     >    |   |  /                  |
  R  >    |   | /                   |
     >    |   |/                    V
     |    |
     |    |                         Virtual Ground
     +----+
     |
     |
     |
     * 0 volts



Note that the virtual ground does not connect to the zero
volt side of the supply, it is a signal ground only.  I
am not sure how much current this tolerates, I've used it
in very low current applications.  I also do not know how
stable such a thing is.  Perhaps our EE members can
enlighten whether this is even a fair idea let alone a good
one.


"Rob" <cyborg_0 at iquest.net> wrote:
>Ok, heres the deal.. Im trying to rescale a 741 based opamp lfo.
>I want it to run off of +5v and 0v. Now, according to most things I have =
>read, it seems that all i really need to do is to reference the unused =
>input of the opamp to about middle voltage ie in this case, 2.5 volts. =
>This should work. Or should it?
>
>Rob

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