[sdiy] Vco I did today...

[Ian Fritz]

At 07:02 PM 1/16/2003, patchell wrote:

>     Yes, but the 2n4391 is a bit on the pricey side...

$0.155 at Newark (SOT package).

>still, I will have to
>endevor to do some tests to see if I can measure any difference between the
>two.  On a casual basis, I have not noticed any performance differences 
>between
>the J111 and the 2n4391 (I have both parts, so I can use both in the exact 
>same
>circuit, keeping the number of variable changes to a minimum).  I am also 
>going
>to see if I can come up with a good way to measure the channel leakage.  I am
>curious if there is a real difference, or if the spec was looser so that more
>parts could potentially pass test...(nothing like depending on typical
>performance to make your life exciting...eh?).

Good points.

I also noticed in the Fairchild table that the capacitances aren't 
specified. Seems odd.

   Ian





>Ian Fritz wrote:
>
> > If you look at the comparison chart given by Farichild, you will see that
> > 25 different parts come from that one process (No. 51).  Most are not all
> > that suitable for the sawtooth VCO application.  I think the best devices
> > are the 2N4391, 2N4859, 2N4091 (all from process 51) and the2N5432 (process
> > 58). To me, the J111 has too much leakage and too little pass current.  A
> > couple of weeks ago I looked around and found that three manufacturers are
> > still producing the 2N4391, which is my choice for the best unit.
> >
> >    Ian
> >
> > At 12:00 PM 1/16/2003, Tim Ressel wrote:
> > >Jim,
> > >
> > >I don't think the J111 and 2N4391 are the same. J111
> > >shows 1nA Idoff, 2N4391 is 0.1nA.
> > >
> > >You're right, Rdson and Idoff tend to be exclusive.
> > >But it makes sense; the combination can be thought of
> > >as the dynamic range of the FET. The question I have
> > >is: which is more important, Rdson or Idoff?
> > >
> > >--tr
> > >
> > >--- patchell <patchell at silcom.com> wrote:
> > > >     I have had no problems with them.  The J111 is
> > > > equiv (well, actually
> > > > the same die as) the 2n4391 which has also been used
> > > > a lot.
>
>--
>  -Jim
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