Full wave rectifier as Saw-to-Tri converter

[terry michaels]

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