[sdiy] TZ triangle core

[Ian Fritz]

At 11:43 AM 3/9/2011, Harry Bissell wrote:
>I'm still playing with the simulation. It works correctly (sort of) but 
>for some reason my polarity  switchers tend to bounce right out of the 
>real world. The last crash was sitting at about 80MV on a transition.

Hmmm ... better dust off the patent filer.  :-)

As you can see by following the signal around the loop, it does have a 
stable state sitting against one of the rails.  I've added a switch across 
the integrating cap and an RC network to short it out for a sec after power on.

For a while I was having trouble with the comparator not switching with 
very slow signals.  Using a faster opamp with a smidge of hysteresis seems 
to have fixed that.

For very low speed operation it is crucial to have offset and symmetry 
trimmers in place.  But of course, there is always trouble at some point, 
just as with any VCO.  I've managed to get about a 500:1 frequency range 
with fixed Iabc and variable linear FM.  Probably I could do better with 
better parts and better matching/trimming for the switchers.  They need to 
be very accurate for low freq operation.

Since this is just a simple ancillary circuit for my TW chaos generator, 
none of this is too critical, since you never sit near zero frequency for a 
long time.

I don't know why your switchers are blowing up.  Is this working in 
isolation, or in the loop?

Ian