[sdiy] Negative content on half wave rectifier

[David G Dixon]

> for proper use of a capacitor the circuit of figure 4 is the 
> only one that works correctly.  In figure 6 the cap works on 
> the inverting input but not the non-inverting input. In Fig.4 
> the last opamp is actually just an inverting summer so the 
> cap works equally well on both polarities...
> 
> ymmv. I have used all these circuits and been burned if I 
> wanted to add a cap. You could always add a low-pass filter 
> (RC or otherwise) at the output of any of these.

In my use of the Figure 6 circuit, I've added the cap across the two diodes
(i.e., between the inverting input of the first opamp and the non-inverting
input of the second) and this seems to work well.  However, I agree with
Harry that caps on these circuits are a bit of a crap-shoot.