Full wave rectifier as Saw-to-Tri converter

[patchell]

    This is a full wave rectifier saw to triangle converter that I did a long
time ago.  (It is the full VCO schematic, but I am sure you can pick out the
full wave rectifier converter).  There were two pots, one to adjust triangle
symetry and one to adjust offset voltage.

http://www.silcom.com/~patchell/tcvco/tcvco.pdf

    -Jim

terry michaels wrote:

> Message text written by Martin Czech
> >I don't understand the circuit.
> What does happen with the first OPAMP if feed with a very
> slow saw ? No dc feedback, should go to rail.
> For negative input there is some feedback via diode,
> but again, what does happen if the cap is already charged?
>
> I don't want to say that this circuit doesn't work,
> but I fell that it is frequency dependend (low end).
>
> ???
>
> m.c.
> <
>
> Hi Martin:
>
> I have to guess the circuit isn't drawn correctly.  To fix it I think you
> need to do this:  reverse the polarity of the diode across the first
> op-amp, and connect a large value resistor from the inverting input of the
> first op-amp to the negative rail. Then the diode will always be forward
> biased.  That will exactly compensate the forward drop of the second diode
> connected between the op-amps.  The transition point for the rectifier will
> then be at the midpoint of the saw wave, zero volts, and is no longer
> temperature dependent.
>
> Terry Michaels

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