[sdiy] Critique my gate output buffer?
Roman Sowa
modular at go2.pl
Mon Dec 9 15:08:48 CET 2024
Yes it can be made faster.
You can add a resistor across base-emiter of the PNP transistor. 100k
should do the trick, 47k even better. You might also lower the load at
output. I suggested 30k, make it 10k, but then again it may be too much
load if you OR 10 ot those outputs together. Which means the circuit
should become faster with more outputs ORed
Roman
W dniu 2024-12-08 o 17:22, Paul Glass-Steel pisze:
> Roman,
>
> I got sidetracked for a bit with holiday guests etc., but I revisited
> this and I believe all the issues I was having were due to my poor
> implementation of a single-transistor version. Your version as
> originally posted seems fine with being shorted to any rail, wire-ORs
> beautifully, and sags very little under even unrealistically demanding
> loads. The only downside I've found so far (as I'm fine with the parts
> count/cost) is that it seems to max out around 12 or 13 KHz (I hope to
> re-measure tomorrow). If there's a way to increase the speed, that
> would be great; if not, that may just be the compromise for offering the
> wire-OR functionality.
>
> Thanks,
> -Paul
>
> On Thu, Nov 28, 2024 at 4:31 AM Roman Sowa <modular at go2.pl
> <mailto:modular at go2.pl>> wrote:
>
> Yes, there is a good way to limit the current, now that I know you use
> 7805 especially for this. Just insert a resistor before 7805. If it's
> powered from +12, then 200 ohm resistor from +12 to 7805 input will
> provide about 30-40mA current limit.
>
> BTW, shorting the output to either GND or -12V should not make any
> difference in dissipated heat for 5V regulator. If that happens,
> probably your base resistor is too low. It's the output transistor that
> should take the heat on itself in this circuit.
> You didn't even mention accidental short to +12V. Your poor 78L05 would
> not approve.
>
> PNP was used there to make gate output go very closely to 5V rail and
> also to provide good ORing capability. You could use NPN working as
> follower too, but then you loose 0.7V and walk on a thin ice having
> outputs in off state with 5V reversed voltage (from other ORed outputs)
> on the emiter.
>
> Roman
>
> W dniu 2024-11-26 o 20:34, Paul Glass-Steel pisze:
> > Roman,
> >
> > Thanks for this - I breadboarded it this morning and it does work
> well.
> > I did note that, though the circuit itself doesn't mind being
> shorted to
> > ground or even to the -12V rail, that doing so does heat up the
> 78L05 I
> > was using. Is there a good way to limit the current in
> fault conditions,
> > without compromising the voltage under load too much? Also, I'd be
> > interested in the technical reasons behind using PNP here, though
> the
> > inverted logic isn't a problem for me.
> >
> > Thanks again,
> > -Paul
> >
> > On Tue, Nov 26, 2024 at 4:29 AM Roman Sowa <modular at go2.pl
> <mailto:modular at go2.pl>
> > <mailto:modular at go2.pl <mailto:modular at go2.pl>>> wrote:
> >
> > I can understand that you want the gate stay at constant
> level even
> > with
> > 30 such outputs OR-ed, hence the 1k inside feedback loop. But
> if you
> > don't need well defined current limit as in this case, why
> not just use
> > PNP transistor? Short circuit current will be limited then by
> base
> > current times beta. Just enough not to blow the transistor up in
> > case of
> > actual shorting outout to GND
> >
> > See the attachment
> >
> > And if your circuit offers reversed gate output somewhere
> anyway, then
> > you can even omit T2.
> > I know opamps may be cheaper now than transistors, but let's not
> > overkill things.
> >
> > Roman
> >
> > W dniu 2024-11-25 o 17:42, Chris McDowell via Synth-diy pisze:
> > > K one more.
> > >
> > > What happens here is the more outputs you OR together in this
> > way, the
> > > lower that 22k looks and the more voltage develops across
> your 1k
> > > resistor, which basically wont ever really matter. I still
> think
> > > tempting your op amp to overshoot or whatever funky thing it
> > wants to do
> > > with your diode and cable capacitance is unnecessary given
> that a
> > 220R
> > > resistor in series with the diode would handle it. or put the
> > parallel R
> > > and C from output to minus input like you know you're
> supposed to :P
> > >
> > > in my personal system, everything has some manner of 100k to
> > ground on
> > > the inputs and I would leave the 22k out entirely. I guess
> what I
> > would
> > > /actually/ do is build an explicit OR module.
> > >
> > > Cheers,
> > > Chris
> > >
> > >> On Nov 25, 2024, at 11:20 AM, Chris McDowell
> > <declareupdate at gmail.com <mailto:declareupdate at gmail.com>
> <mailto:declareupdate at gmail.com <mailto:declareupdate at gmail.com>>>
> > >> wrote:
> > >>
> > >> This is like swapping your output resistor with a diode,
> which
> > means
> > >> your capacitive load is only, yknow, capacitively loading
> when the
> > >> diode is conducting. I don't think there is a lot of value in
> > putting
> > >> the output resistor in the feedback loop for gate
> outputs, as we'd
> > >> usually do that to increase DC accuracy at the receiving
> > equipment. I
> > >> would move your output resistor out of the feedback loop
> to take
> > >> stability out of the conversation. You then have
> something pretty
> > >> normal that will OR with similar outputs, up to some
> limit where
> > all
> > >> your 100ks (and whatever all the various input
> resistances) in
> > >> parallel are too low a resistance to get your gates across.
> > that's a
> > >> lot, though.
> > >>
> > >> Cheers,
> > >> Chris
> > >>
> > >>> On Nov 24, 2024, at 12:42 PM, Paul Glass-Steel via Synth-diy
> > >>> <synth-diy at synth-diy.org
> <mailto:synth-diy at synth-diy.org> <mailto:synth-diy at synth-diy.org
> <mailto:synth-diy at synth-diy.org>>> wrote:
> > >>>
> > >>>
> > >>> I'm hoping to improve on the typical transistor
> emitter-follower,
> > >>> wire-OR capable gate output buffer that many of my modules
> > >>> have inherited from CGS and NLC. I've come up with this:
> > >>> https://tinyurl.com/259pt83t
> <https://tinyurl.com/259pt83t> <https://tinyurl.com/259pt83t
> <https://tinyurl.com/259pt83t>>
> > <https://tinyurl.com/259pt83t <https://tinyurl.com/259pt83t>
> <https://tinyurl.com/259pt83t <https://tinyurl.com/259pt83t>>> - it
> > >>> seems happy on my bench, the voltage is stable under a
> lot of
> > fan-out
> > >>> to multiple inputs and it seems ok with long cables /
> capacitive
> > >>> loads. But I thought I'd check here to see if I'm missing
> > something.
> > >>>
> > >>> Thanks,
> > >>> -Paul
> > >>>
> > >>>
> > >>> ________________________________________________________
> > >>> This is the Synth-diy mailing list
> > >>> Submit email to: Synth-diy at synth-diy.org
> <mailto:Synth-diy at synth-diy.org>
> > <mailto:Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>>
> > >>> View archive at:
> https://synth-diy.org/pipermail/synth-diy/
> <https://synth-diy.org/pipermail/synth-diy/>
> > <https://synth-diy.org/pipermail/synth-diy/
> <https://synth-diy.org/pipermail/synth-diy/>>
> > >>> Check your settings at:
> > https://synth-diy.org/mailman/listinfo/synth-diy
> <https://synth-diy.org/mailman/listinfo/synth-diy>
> > <https://synth-diy.org/mailman/listinfo/synth-diy
> <https://synth-diy.org/mailman/listinfo/synth-diy>>
> > >>> Selling or trading? Use marketplace at synth-diy.org
> <mailto:marketplace at synth-diy.org>
> > <mailto:marketplace at synth-diy.org
> <mailto:marketplace at synth-diy.org>>
> > >
> > > ________________________________________________________
> > > This is the Synth-diy mailing list
> > > Submit email to: Synth-diy at synth-diy.org
> <mailto:Synth-diy at synth-diy.org>
> > <mailto:Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>>
> > > View archive at:
> https://synth-diy.org/pipermail/synth-diy/
> <https://synth-diy.org/pipermail/synth-diy/>
> > <https://synth-diy.org/pipermail/synth-diy/
> <https://synth-diy.org/pipermail/synth-diy/>>
> > > Check your settings at:
> > https://synth-diy.org/mailman/listinfo/synth-diy
> <https://synth-diy.org/mailman/listinfo/synth-diy>
> > <https://synth-diy.org/mailman/listinfo/synth-diy
> <https://synth-diy.org/mailman/listinfo/synth-diy>>
> > > Selling or trading? Use marketplace at synth-diy.org
> <mailto:marketplace at synth-diy.org>
> > <mailto:marketplace at synth-diy.org
> <mailto:marketplace at synth-diy.org>>
> >
>
More information about the Synth-diy
mailing list