[sdiy] Mind blown -- TL074 saturated outputs different
David G Dixon
dixon at mail.ubc.ca
Wed Nov 28 09:50:28 CET 2018
Thanks, René. I think I will add an output resistor and a couple of zeners
to set the output voltages of the comparators to certain values, as in the
"precision schmitt trigger" of the link you provided. I need to rely on a
fixed output voltage to generate the specific positive and negative
threshold voltages for the comparator logic, and I can achieve this with the
Tomorrow morning I'll get this damned thing finished. Someone in Iceland is
waiting patiently, but I think I'll have to lay out and make a new board.
Oh well, that's why we build prototypes in the first place.
Oh, and in case anyone is wondering, I am actually losing a little money on
this one (plus, it's taking many hours of my time which I am providing for
> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On
> Behalf Of René Schmitz
> Sent: Tuesday, November 27, 2018 11:44 PM
> To: synth-diy at synth-diy.org
> Subject: Re: [sdiy] Mind blown -- TL074 saturated outputs different
> Hi David and all,
> On 28.11.2018 08:06, David G Dixon wrote:
> > I thought that opamps of a certain flavour would always saturate a
> > certain fixed voltage away from the rail voltage, because this was
> > determined by internal diode drops, which are basically
> fixed. Was (am) I smoking crack?
> Even the diode drops varies with loading.
> > Does everybody else know about this and I'm just finding out about
> > after 10 solid years of electronics? Or am I just experiencing
> > particularly bad luck with my ICs?
> I would say it is generally avoided to rely on the saturation
> voltage to be a specific value.
> That is why people will use schemes like this if you need any
> Maybe use a rail-to-rail output opamp instead. (Even these
> will a small bit away from the rail.)
> synth at schmitzbits.de
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