SV: Re: SV: [sdiy] More MOSFET saw VCOs

[harrybissell]

since we are plating with reset circuits...

I'm using an NPN to reset a sawtooth core... the opamp with
capacitor feedback type.

In my case... I allow it to ramp up to an unknown voltage. It
clips at 7V.  I'd expect that to go higher...

Am I seeing base-emitter breakdown, in your humble opinions ?
That would be about the right voltage for that to happen. OTOH
the emitter is at the summing junction (so that is ground) and the
collector at the output (which is positive) so where is this happening ?

H^) harry  (you did not expect work to stop for holidays ???)

karl dalen wrote:

> --- Ian Fritz <ijfritz at earthlink.net> skrev:
>
> > At 06:22 PM 12/22/05, karl dalen wrote:
> > >There is a parameter that says "gate capacitance changes
> > >with frequency"!
> > >
> > >Do you se any differences regarding this parameter?
> >
> > Hmmm ... interesting question.  Anyone know the answer?  :-)
> >
> > There are other odd effects, too, like change in on resistance with
> > voltage.
>
> Yes, but thats a well known one!
>
>  I suppose the gate capacitance mostly comes into play during the
> > discharge phase, which shouldn't depend on the VCO frequency.  But if there
> > is some feedthrough during the ramp ...
>
> Most likely if it was a power mos,
> the decay curve is very exponential.
>
> I think the variation of Vgs is a problem, wheter this
> is diffrenet between devices or the same for one entire batch
> im not to shure but temp and voltage will do change it!
>
> > The waveform isn't perfect and changes a bit with frequency.  So maybe
> > these effects come into play.  To first order, though, tracking is very
> > good and that's the main thing.
>
> I had also quite good tracking but the overshot/ringing
> at start of retrace caused tri wave be a bit messy at higher
> frequencies! Could be filtered by small pf cap ofcourse!
>
> Well, Ian was it 1,5 years ago or not??
>
> REg
> KD