Can somebody take a peek at this circuit for me?

[John Larkin]

On Wed, 23 Mar 2005 10:46:39 +0100, "Fred Bartoli"
<fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote:

"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> a écrit dans le message
de news:4240D84B.150509C3@hotmail.com...

Leon Heller wrote:

Why not simulate it? If it simulates OK you can actually build it and
see
what happens.

Simulation regrettably doesn't simulate the fire caused by kilowatts of
dissipation in the feedback Rs !


This could be a nice add-on to EWB

One of the simulators had a little animated flame that popped up over
parts that were way over their rated dissipation. Can't remember which
one.

But in my most humble opinion, EWB is way-overpriced crud. I bought it
with the guaranteed lifetime upgrade, so they changed the name to
Multisim to weasel out. Their transmission-line model was screwed,
too.

John

 

[John Larkin]

On Tue, 22 Mar 2005 21:36:25 -0800, "Larry Brasfield"
<donotspam_larry_brasfield@hotmail.com> wrote:

Let's review the sequence of events here:
0. JF posts a schematic.
1. LB posts "cannot oscillate ... Study it carefully".
2. LB spots an error in said post and cancels it.
3. LB posts, 13 minutes after 1, about loop gain and dominant poles.
4. JF replies to something by quoting the cancelled post, 2 hours
and 32 minutes after post 3, (the correction) was posted.
5. LB replies, informing JF that post 1 cancelled, post 3 is up,
and claiming confidence that JF designed an oscillator.
6. JF replies, 1 hour and 13 minutes later, noting that posts 1 and 5
are inconsistent, suggests post 5 should be called "backpedaling".

Larry, let it go. It's only a newsgroup.

John

 

[John Larkin]

On Wed, 23 Mar 2005 02:53:28 +0000, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:

Paul Burke wrote:

I think that Mr. Genome is suggesting that the circuit is trivial: if
you don't KNOW whether it will work or not, you should get one of the
electronic department's technicians to look at it for you and swap wages
with him. I think he might be rather afraid that you are one of the
teaching staff of some academic institution.

Reminds me of the year almost completely wasted I spent at the supposedly
prestigious University College London.

I realised the course was junk so went on to do other things. One memorable
comment from one of the friends I made on the sourse was " we've passed the
end of year exams but still don't know what a transistor does ".

Somewhat ironically, I already did understand before I even left school.

They did try to teach me how to analyse stresses in bridges though. (
because it's an *engineering* degree you're apparently supposed to know this
mechanical stuff ! in case you need to design transmission towers I was told
as an excuse ). They failed on account of the droning twat teaching what's
possibly the most boring subject in the world sending me to sleep regularly.

Yeah, most of that mechanical stuff was stupefyingly dull. Worse, I
had 8AM classes, and the instructor kept throwing erasers at me
whenever I fell asleep.

Thermo was good, except that it was too theoretical. Some serious,
practical things about heat flow and stuff would have been much better
for EEs.

John

 

[Jim Thompson]

On Wed, 23 Mar 2005 08:14:58 -0800, John Larkin
<jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote:

On Tue, 22 Mar 2005 21:36:25 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:


Let's review the sequence of events here:
0. JF posts a schematic.
1. LB posts "cannot oscillate ... Study it carefully".
2. LB spots an error in said post and cancels it.
3. LB posts, 13 minutes after 1, about loop gain and dominant poles.
4. JF replies to something by quoting the cancelled post, 2 hours
and 32 minutes after post 3, (the correction) was posted.
5. LB replies, informing JF that post 1 cancelled, post 3 is up,
and claiming confidence that JF designed an oscillator.
6. JF replies, 1 hour and 13 minutes later, noting that posts 1 and 5
are inconsistent, suggests post 5 should be called "backpedaling".


Larry, let it go. It's only a newsgroup.

John

Search on: "Larry Brasfield" ex-employee Microsoft ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Jim Thompson]

On Wed, 23 Mar 2005 08:19:30 -0800, John Larkin
<jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote:

On Wed, 23 Mar 2005 02:53:28 +0000, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:


Paul Burke wrote:

I think that Mr. Genome is suggesting that the circuit is trivial: if
you don't KNOW whether it will work or not, you should get one of the
electronic department's technicians to look at it for you and swap wages
with him. I think he might be rather afraid that you are one of the
teaching staff of some academic institution.

Reminds me of the year almost completely wasted I spent at the supposedly
prestigious University College London.

I realised the course was junk so went on to do other things. One memorable
comment from one of the friends I made on the sourse was " we've passed the
end of year exams but still don't know what a transistor does ".

Somewhat ironically, I already did understand before I even left school.

They did try to teach me how to analyse stresses in bridges though. (
because it's an *engineering* degree you're apparently supposed to know this
mechanical stuff ! in case you need to design transmission towers I was told
as an excuse ). They failed on account of the droning twat teaching what's
possibly the most boring subject in the world sending me to sleep regularly.




Yeah, most of that mechanical stuff was stupefyingly dull. Worse, I
had 8AM classes, and the instructor kept throwing erasers at me
whenever I fell asleep.

Thermo was good, except that it was too theoretical. Some serious,
practical things about heat flow and stuff would have been much better
for EEs.

John

At MIT, the EE Honors majors had to take non-major electives in
classes as if they were majoring them... clear as mud I know ;-)

But I had to take mechanical engineering courses that weren't watered
down to make them into electives. Likewise math and physics.

I found most of them very enjoyable and instructive.

Except for atomic physics :-(

Any MIT lurkers from my era will recognize the phrase, "Pless is a
Plick" ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Charles Edmondson]

Pooh Bear wrote:

Leon Heller wrote:


Why not simulate it? If it simulates OK you can actually build it and see
what happens.


Simulation regrettably doesn't simulate the fire caused by kilowatts of
dissipation in the feedback Rs !


Graham

Unless, of course, you have PSpice Advanced Analysis, with its Smoke

feature turned on...

 

[Jim Thompson]

On Wed, 23 Mar 2005 08:42:01 -0800, Charles Edmondson
<edmondson@ieee.org> wrote:

Pooh Bear wrote:
Leon Heller wrote:


Why not simulate it? If it simulates OK you can actually build it and see
what happens.


Simulation regrettably doesn't simulate the fire caused by kilowatts of
dissipation in the feedback Rs !


Graham

Unless, of course, you have PSpice Advanced Analysis, with its Smoke
feature turned on...

Or create your own SOA (hot electron) checkers for fine-feature-size
CMOS ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Michael Noone]

John Larkin <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote in
news:mop1411hd4a9jdgbm8oomk0vldiqrd2ph2@4ax.com:

On Tue, 22 Mar 2005 11:54:38 -0600, Michael Noone
mnoone.uiuc.edu@127.0.0.1> wrote:

"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in
news:8HS%d.1$e%3.253@news.uswest.net:


You should learn to say what a circuit has to do in
terms of performance, preferably quantifiable. I
could say your circuit will "work", because you
have not really specified what that means.

Well - right now I just want to see if it even sort of works - but
eventually I want a circuit that can amplify a 0-10V signal to 0-400
with response time of about 1ms and with accuracy to the nearest volt
on the output.


I did post my little HV amplifier circuit to a.b.s.e. a while back. It
uses an opamp driving a pair of high-voltage optocouplers, with the
phototransistor sides as the output totem pole across the 400 volt
supply. This eliminated all sorts of level shifting problems... lets
light do it! It should be about good for 1 mA drive from 400 volt
rails.

What are you going to drive?

John

Hi John - it will be driving some sort of fluid load. I've been told
that it should be able to sync 0-20ma though this fluid. I looked
through ABSE and didn't find your circuit. My NG server has about 30 day
retention - so it should still be there... Do you have any idea what the
filename or topic name was? Thanks,

-Michael

 

[Michael Noone]

John Larkin <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote in
news:0j5341l1vjnqllstunbn4e4893rftq1p09@4ax.com:

Yeah, most of that mechanical stuff was stupefyingly dull. Worse, I
had 8AM classes, and the instructor kept throwing erasers at me
whenever I fell asleep.

Thermo was good, except that it was too theoretical. Some serious,
practical things about heat flow and stuff would have been much better
for EEs.

John

One of my chem TAs always threw erasers at me. Twas probabaly for the best
though - otherwise I would have slept through that entire class.

-Michael

 

[Michael Noone]

Fred Bloggs <nospam@nospam.com> wrote in news:42418791.4020408
@nospam.com:

John Fields wrote:
On Tue, 22 Mar 2005 10:17:27 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:



You're welcome. I've set followups to sci.electronics.basics
because this kind of discussion is more topical there.


---
Goddam, but you're a pompous little chickenshit fuck, aren't you?
Who
the hell died and left you as the arbiter of what should go where?


Looking at SEB, the sorry-assed fake and windbag still has not
responded
to the OPs criticism of his pathetic excuse for a "solution" circuit
without a single component specified. Given Brasfield's ignorance, it
may require hundreds of hours of mindless simulation of anything he
dares to specify- it should also be clear by now that the fake doesn't
have much of a knowledge base when it comes to components- if that
isn't
a giveaway that he's 100% mouth with absolutely no action I don't know
what is. But he seems to be impressing members of the pompous,
pseudo-sophisticated, windbag clique of self-appointed authorities on
SED. Isn't that telling....And the fraud is most likely suckering the
juvenile punk OPs with that totally fake Socratic style- it is fake
because Socrates used it to actually steer the dialogue to a
pre-determined goal, whereas Brasfield uses it to go nowhere, just a
lot
of dodging, pompous pseudo-intellectual language, used to conflate the
issues and make himself look smart to the lesser educated people.
Quite
telling that zero and reject is so desperate for esteem that he stoops
to that level of abuse.

I'm not sure about this - but I'm getting this nagging suspicion that

you aren't in love with Mr. Brassfield. Correct me if I'm wrong though.
Regards,

-Michael

 

[Larry Brasfield]

"John Fields" <jfields@austininstruments.com> wrote in message
news:8n7341pqags1l6l9htraduvcua0509euh9@4ax.com...

On Tue, 22 Mar 2005 12:50:32 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:

"John Fields" <jfields@austininstruments.com> wrote in message
news:emr041dnld7pmj6v7emf5bdsvng962tqgv@4ax.com...
+400V>--+-----+---D S---+----------+-------->>--+
| | G | | |
| | | [ZENER] | |
[R1] [R2] | |K | |
| | +-----+ | |
| | | | |
| +-----+ | |
| | | |
+-------------------+ Vin [R2] |
| | | | | |
| D /-|--+ | [RL]
|K G---< | | |
[REF] S \+|-------+-----+ |
| | | | | |
| | | [R3] [C1] |
| | | | | |
GND>----+-----------+-------+--------+-----+-->>--+


Use a little high-voltage FET to drive the big FET's gate. They're
cheap and it doesn't take much (damn near nothing) to drive them. Use
a micropower opamp and you can get its supply voltage from a resistor
and a low-current shunt reference tied to the 400V rail (or even just
a resistive divider) The Zener is to make sure the big MOSFET's gate
voltage never goes higher than it's supposed to, WRT to the source,
R2 R3 is the 40:1 divider, and C1 is to keep the thing from
oscillating.

What do you think the maximum output will be and
how does that compare with the "requirement"?

Would you increase C1 until it formed the dominant
pole in that loop?

Where do think that would be, considering where the
the previously dominant pole is (likely to be)?

How much loop gain variation would you expect to
see as the operating point changes?

---
For the answer to all of your questions, if you've taken the trouble
to download LTC's excellent simulator, run bitethedust.asc which you
can find at abse under the subject: "Bite the dust, asshole"

Quite a few points in one sentence, so I will answer them
in order, with a number to deliniate them.

1. Using simulation is not the right place to answer those
questions, especially when considering a set of topologies.
The simulator can be used to confirm (or refute) one's
understanding of a circuit, but it shares many of the pitfalls
of prototypes. It is a way of seeing how a specific
collection of components, with a specific set of parameters
and values, will behave. (And keep in mind, those parts
may correspond to no real part if the models are faulty.)
Saying "My circuit is good!" because you see something
you wanted to see out of a simulation is folly.

2. I have used LTSpice for a few years for quick
and dirty work.

3. I did acquire your strangely named sim file. It
is a vigorous oscillator. If you took the output
from the op-amp with suitable limiting, you could
use it as a crude VCO.

4. Name-calling is the recourse of those who find
it difficult to formulate a rational argument.

Here are some short answers to my questions,
evident from a very brief analysis (of your posted
circuit which had no values or part types) and
confirmed by watching your oscillator with SPICE
(with the quoted questions copied from above):

What do you think the maximum output will be and
how does that compare with the "requirement"?

The requirement was 0 V to +400 V out. The
above schematic necessarily produces less than
that, subtracting at least a PMOS gate threshold.

The simulation does much lower due to part selection
apparently limited to the LTSpice standard library.

Would you increase C1 until it formed the dominant
pole in that loop?

That is the only way to make the circuit stable, but
the response becomes so slow that simulating it is
a challenge. (a challenge I had no patience for)

Where do think that would be, considering where the
the previously dominant pole is (likely to be)?

Way closer to 0 than the 3 to 30 Hz typical location
of the op-amp. "Way" has magnitude similar to the
circuit's excessively high low frequency loop gain.

How much loop gain variation would you expect to
see as the operating point changes?

The circuit in question, for the output range required,
(or limiting same to the deliverable output range),
has an extremely wide range of loop gain because
the common source FET current goes from very
near 0 to values many times higher. This greatly
complicates the task of designing the loop for
stability. In the simulation, this fact, (together with
the fact that it was not designed for stability), is
the reason the circuit acts like a VCO.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Michael Noone]

Winfield Hill <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote in
news:d1s0fj02dv5@drn.newsguy.com:

Michael Noone wrote...

Hi - can somebody tell me if this circuit would work, or if it would
come even close to working?
https://netfiles.uiuc.edu/mnoone/www/Linearamplifierwithfet.jpg
The circuit is supposed to amplify a 0-10V signal to 0-400V.

Sorry, Michael, your circuit is not even close. First, you have
no load on the drain of the FET, unless you consider your feedback
resistor to be a load. Second, where do you apply the 400V supply,
to the Vss pin? Does Vss = -400V (normally Vss is taken to mean more
negative voltages (i.e. "sources of N-channel FETs) and Vdd is taken
to mean more positive voltages (drains)? No, the BSS92 is a p-type
FET, so Vss must be +400V. Oops, Third, the FET will blow its brains
out when you turn on the 400V because 1) you exceeded the +/-20V Vgs
rating, and 2) you exceeded the 240V Vds rating. Fourth, after
solving the drain-connection problem, and the excess voltage
problems, you'll find the feedback network is unstable, because it
has too much loop gain, and too much phase shift. Fifth, you'll
learn FET capacitances and load capacitances (e.g. a connecting coax
cable) are a big issue, so you'll need an active way to both pull up
and pull down the output. In general, Sixth, with MOSFETs, you'll
also need a way to isolate the opamp from driving the high gate
capacitance of typical high-voltage power MOSFETs. Even the BSS92,
which is not a true high-voltage power MOSFET, has nearly 200pF of
gate capacitance at low voltages (see the Siemens datasheet page 7).

Oops - I always get vss, vdd, vcc, etc. confused. I meant +400V by it
though. Also - the fet choice was almost entirely random - I just chose
it because it was the proper type.

Thanks for your note about driving FETs - I hadn't realized that was an
issue.

Seventh, Spice is NOT a good way to evaluate this type of circuit,
in part because once you find a good 500V FET, and if you investigate
sufficiently, you'll find that the power MOSFET spice models are very
poor for low-current-density linear operation. They're designed for
analyzing switching performance. And most are rather poor at that.

Spice tis not a worry - being that I haven't a clue how to use it

Spice is also not a good way to study such circuits because you'll
learn very little, compared to studying MOSFET linear operation, and
applying simple analytical circuit-operation calculations. I suggest
you get a copy of our book, The Art of Electronics, and read chapter
3. In it you'll also find an example of a high-voltage FET amp that
works.

I looked through chapter three and didn't see it. Or are you speaking of
the piezo driver circuit?

Thanks for your help,

-Michael J. Noone

 

[Michael Noone]

John Fields <jfields@austininstruments.com> wrote in
news:g0k24158d9glfoqdgf0o5jcmglinvdmevj@4ax.com:

On Wed, 23 Mar 2005 01:17:04 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:


The prophesy was: John's circuit "will oscillate".

---
And it did. Big deal. It's now fixed, and I can only surmise that
since you didn't have your big gums flapping something to the effect
of: "...and here's a fix that even Fields should have known about,
blah, blah, blah..."

If you can get your sorry ass over to abse and download the file you
might learn something, even though you'd never admit it.

Goodbye for now.

Hi Mr. Fields - could you post what the corrected version of your circuit
is? Thanks so much for your help,

-Michael J. Noone

 

[Larry Brasfield]

"John Fields" <jfields@austininstruments.com> wrote in message
news:v8n2419cmg5f10kqrpancqspv0aiaib3en@4ax.com...

On Wed, 23 Mar 2005 05:29:37 -0600, John Fields
jfields@austininstruments.com> wrote:
On Wed, 23 Mar 2005 01:17:04 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:

The prophesy was: John's circuit "will oscillate".
---
And it did. Big deal.

Actually, I think it is a big deal.

If you posted it knowing it to be an oscillator, it proved
nothing with respect to my points and was a disservice
if intended for the OP.

If you posted it without recognizing the oscillation for what
it is, then, at the very least, you have exhibited a level of
competence that disqualifies you from holding yourself out
as one of my technical betters. Perhaps that will cease.

It's now fixed, and I can only surmise that
since you didn't have your big gums flapping something to the effect
of: "...and here's a fix that even Fields should have known about,
blah, blah, blah..." , that you didn't know how to fix it.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Added_________________/

(Looks like that pretense is not going to cease. Sigh.)

That is the purest speculation. Why in the world should I
try to fix a misconceived circuit? As far as I am concerned,
your topology is/was deeply flawed. To "fix" it, I would
simply replace it with the topology I posted earlier. As I
discovered in just a few minutes this morning, my circuit
can be given values that are easily determined by a simple
analysis and works right away with a decent response that
is stable over the active output range.

If you can get your sorry ass over to abse and download the file you
might learn something, even though you'd never admit it.

I am thankful that you are not familiar with my ass.

Before I even think of downloading that file, I would
want to know that it was not an oscillator. Given your
distinctions so carefully made yesterday between its
"ripple" and "oscillation", and the fact that you have not
owned up to being terribly mistaken, I am extremely
skeptical that any technical education awaits me at
your hands. The mere suggestion is laughable in this
context and proves you to be entirely shameless.

Maybe to regain some credibility, you should reveal
what kind of thinking led you to believe that your
amplifier could have visible AC output without any
AC input and not be considered an oscillator.

....
--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Fred Bartoli]

"John Larkin" <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> a écrit dans
le message de news:i5534191hh6jfqsbcgshl7s6knedtivek9@4ax.com...

On Wed, 23 Mar 2005 10:46:39 +0100, "Fred Bartoli"
fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote:


"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> a écrit dans le
message
de news:4240D84B.150509C3@hotmail.com...

Leon Heller wrote:

Why not simulate it? If it simulates OK you can actually build it and
see
what happens.

Simulation regrettably doesn't simulate the fire caused by kilowatts of
dissipation in the feedback Rs !


This could be a nice add-on to EWB

One of the simulators had a little animated flame that popped up over
parts that were way over their rated dissipation. Can't remember which
one.

Wow, that would make a nice simulator for m$ to buy, and improve, with lots
of animated components. Just think of how useful it will be if you could
place trimmers here and there, then tweak your circuits using a mouse driven
screw driver.
And what an exciting experience when, tweaking your circuit, you suddently
hear a nice prrshhhhh...pfff...pop, all that real time synthesized in Dolby
5.1, with a nice animated stereo view of a flame you can look at with a m$
LCD glasses.

But in my most humble opinion, EWB is way-overpriced crud. I bought it
with the guaranteed lifetime upgrade, so they changed the name to
Multisim to weasel out. Their transmission-line model was screwed,
too.

Yup. I've once had it installed on my PC for about 2 hours when I was hired
by a firm that bought it before I came in.
A real piece of trashware.
I mentioned it because, IIRC, it's the one that had those useless built-in
bench instruments, animated Leds, seven segments led displays and an whole
bunch of the same kind crappy 'features'.

I wonder what it is now they've changed it's name.


--
Thanks,
Fred.

 

[Larry Brasfield]

"Michael Noone" <mnoone.uiuc.edu@127.0.0.1> wrote in message
news:Xns96228794074C3mnooneuiucedu127001@216.196.97.136...

John Fields <jfields@austininstruments.com> wrote in
news:g0k24158d9glfoqdgf0o5jcmglinvdmevj@4ax.com:

On Wed, 23 Mar 2005 01:17:04 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:

The prophesy was: John's circuit "will oscillate".
---
And it did. Big deal. It's now fixed, and I can only surmise

Surmise is worth very little in these matters.
....

If you can get your sorry ass over to abse and download the file you
might learn something, even though you'd never admit it.

Ok, I got my happy ass over there and got John's
latest version, still named in his scat venting manner.

There are deep electronical lessons to be learned
from it that one could conceivably miss while sitting
thru several quarters of frequency domain analysis
and control theory classes. For the benefit of the
NG, I will humbly try to elaborate them:

1. It is possible to close a feedback loop with an
op-amp integrator, then, by turning its gain
down far enough, get the loop to be stable.

2. Excess phase problems induced by the insertion
of a useless resistor between a FET gate and its
original input can be mitigated to some extent by
adding a zero into the integrator response at a
completely different frequency than the needless
pole created by the useless resistor.

3. When no effort has been made to stabilize the
gain of stages within the feedback loop, it remains
possible to stabilize the loop by turning integrator
gain down far enough, provided one is willing to
accept less predictable response.

I humbly admit to having learned these lessons at
various times in the past, one of them from John.

Hi Mr. Fields - could you post what the corrected version of your circuit
is? Thanks so much for your help,

Since Mr. Fields appears busy, I will answer:

If you are willing to adapt his circuit to your
needs, it is what he posted yesterday except
with these mods:

1. Break the setpoint input and reconnect
with a 10K resistor.

2. Add a 100nF cap between the op-amp
output and its inverting input.

3. Add a 1000 Ohm resistor between the
op-amp output and the gate. (Do not try
to calculate the optimum value if you want
the resistor there.)

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Fred Bartoli]

"Fred Bartoli"
<fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> a écrit dans
le message de news:4241d798$0$2778$626a14ce@news.free.fr...

I wonder what it is now they've changed it's name.

Oops.

I apostrophe (French verb for 'heckle') myself before the apostrophe cop do.

"I wonder what it is now they've changed its name."


--
Thanks,
Fred.

 

[Larry Brasfield]

"John Fields" <jfields@austininstruments.com> wrote in message
news:1om341dqi2m5qvm99tv6bilfhtkjl1joad@4ax.com...

On Wed, 23 Mar 2005 10:50:22 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:

"John Fields" <jfields@austininstruments.com> wrote in message
news:8n7341pqags1l6l9htraduvcua0509euh9@4ax.com...
On Tue, 22 Mar 2005 12:50:32 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:
....
Would you increase C1 until it formed the dominant
pole in that loop?

Where do think that would be, considering where the
the previously dominant pole is (likely to be)?

How much loop gain variation would you expect to
see as the operating point changes?

---
For the answer to all of your questions, if you've taken the trouble
to download LTC's excellent simulator, run bitethedust.asc which you
can find at abse under the subject: "Bite the dust, asshole"


Quite a few points in one sentence, so I will answer them
in order, with a number to deliniate them.

1. Using simulation is not the right place to answer those
questions, especially when considering a set of topologies.
The simulator can be used to confirm (or refute) one's
understanding of a circuit, but it shares many of the pitfalls
of prototypes. It is a way of seeing how a specific
collection of components, with a specific set of parameters
and values, will behave. (And keep in mind, those parts
may correspond to no real part if the models are faulty.)
Saying "My circuit is good!" because you see something
you wanted to see out of a simulation is folly.

---
If, for some reason, you feel compelled to perform an in-depth, hand
analysis of the circuit, then by all means do it and report back to
me with what you find.

There is no point in doing such work for that circuit.

Also, if you think that simulation isn't the
way to go, then I suggest you fly your reasons by some of the folks
who make a living doing simulation and see how far you get. I'm sure
Jim Thompson, for one, will see the error of his ways and join you on
the bench with a good ol' Weller soldering gun and a roll of 30-70
solder in hand just champing at the bit to go to work on your newest
project. And, you put down simulation while in nearly the same breath
stating that you found that my circuit oscillated _during_ simulation,
LOL!!! That, AFTER you declared, pre-simulation, that there was NO
WAY my circuit would oscillate regardless of the value of capacitance
on the opamp input. Amusing how you just can't seem to keep your foot
out of your mouth...

Your "LOL" is based on a false premise, one which you
surely knew to be false many hours ago.

As you have seen, my best prediction, the one not from a
post I already told you I had canceled and replaced, was
that your circuit "will oscillate". I predicted this with high
confidence hours before I looked at your circuit with
component values plugged in. You already know this.

Ironically, I detected the oscillation of your circuit before
you did, (unless you are a trickster), writing:
Where did the output ripple come from? I can
see no source for it in your schematic other
than an oscillation. I'm about 95% confidant
that it will oscillate until C1 becomes huge.
The only question is where the limiting occurs.
I had no need to simulate it to see that.

Your point taking is quite premature and deceptive.

Your comedy about prefering soldering over simulation
is a fantasy not supported by my words. As I stated,
both suffer from certain pitfalls that make them a poor
substitute for analysis.

2. I have used LTSpice for a few years for quick
and dirty work.
---
So what did you think my circuit was? Something _not_ quick and
dirty? You're a joke.

I use another simulator for other types of work.
My comment was not about your circuit.
Your proclamations are wearisome.

3. I did acquire your strangely named sim file. It
is a vigorous oscillator. If you took the output
from the op-amp with suitable limiting, you could
use it as a crude VCO.
---
"If frogs had wings" again?
See above, LOL!

Do you deny that the oscillation frequency is a
strong function of operating point?

4. Name-calling is the recourse of those who find
it difficult to formulate a rational argument.
---
True or not, _you_ still remain an asshole.

Believe me, I appreciate your opinion, more than you
can possibly imagine. Having fun?

Here are some short answers to my questions,
evident from a very brief analysis (of your posted
circuit which had no values or part types)

---
I showed no values or part types because it was my intent to present a
topology for consideration, not a fully fleshed out, tested and
guaranteed circuit. To someone skilled in the art that would have
been readily apparent.

That was readily apparent to me. In fact, it would
take a moron to believe an analog circuit without
component values could be "tested and guaranteed".

So, how would you predict the correlation between
"skilled in the art" and ability to spot oscillation at a
high enough level to not hide within resolution limits?

You, however, even mistook the pass transistor
for PMOS even though the drain terminal "D" was clearly shown as being
connected to the high-voltage supply positive.

I will admit to this foolishness: My initial look at the circuit
was thrown off by its similarity to the OP's and its apparent
objective to reach the same output level. I thought, given its
clear inability to do that, that you had simply gotten the
transistor reversed. I soon saw that error and cancelled my
post based upon it.

confirmed by watching your oscillator with SPICE
(with the quoted questions copied from above):
---
Perhaps, because of the vagaries of simulation, it was an artifact?

Are you trying to suggest that your oscillator was a victim
of "vagaries of simulation"? That really takes the cake.

What do you think the maximum output will be and
how does that compare with the "requirement"?

The requirement was 0 V to +400 V out. The
above schematic necessarily produces less than
that, subtracting at least a PMOS gate threshold.
---
Trivial to fix; merely increase the source voltage as required for the
headroom needed.

Or use a more efficient configuration with much
less supply sensitivity. Not too hard, either.

NMOS. Old habits die hard, huh?

Take a point. More will hurt your credibility.

The simulation does much lower due to part selection
apparently limited to the LTSpice standard library.

Would you increase C1 until it formed the dominant
pole in that loop?

That is the only way to make the circuit stable, but
the response becomes so slow that simulating it is
a challenge. (a challenge I had no patience for)
---
The _only_ way? Methinks your naivete is showing. You apparently
haven't seen the circuit modification performed after Mr. Genome so
kindly critiqued my circuit. Check it out and run the simulation.
It's on abse under "Bite the dust, asshole", just like last time.

Your new circuit is a wonder addressed in a later post.
You have every right to take some pride in it. But it is
not "the circuit". Let's not forget the context. The OP
is given a specific configuration without values, and told
how to stabilize it by changing one. That is "the circuit".

However, I will admit to a slight overstatement. Another
way to stabilize it would be to replace the little triangle
with something having a much different gain characteristic
than op-amps being sold today. Take another point.

In the future, you may not accurately construe my use of
the phrase "X circuit" as meaning "any circuit with more
or less similar performance or desired performance".

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Pooh Bear]

John Woodgate wrote:

I read in sci.electronics.design that Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote (in
4240DA27.186F8457@hotmail.com&gt about 'Can somebody take a peek at this
circuit for me?', on Wed, 23 Mar 2005:

Reminds me of the year almost completely wasted I spent at the
supposedly prestigious University College London.

When was this? It sounds quite like my experience at another UL college.
The only good one for electronics was Imperial, but I didn't know that
at the time.

1972-1973.

I actually had an offer from Imperial but wasn't aware that UCL was duff.
UCL seemed like a more interesting college to go to.

Graham

 

[John Larkin]

On Wed, 23 Mar 2005 21:54:43 +0100, "Fred Bartoli"
<fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote:

"John Larkin" <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> a écrit dans
le message de news:i5534191hh6jfqsbcgshl7s6knedtivek9@4ax.com...
On Wed, 23 Mar 2005 10:46:39 +0100, "Fred Bartoli"
fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote:


"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> a écrit dans le
message
de news:4240D84B.150509C3@hotmail.com...

Leon Heller wrote:

Why not simulate it? If it simulates OK you can actually build it and
see
what happens.

Simulation regrettably doesn't simulate the fire caused by kilowatts of
dissipation in the feedback Rs !


This could be a nice add-on to EWB

One of the simulators had a little animated flame that popped up over
parts that were way over their rated dissipation. Can't remember which
one.


Wow, that would make a nice simulator for m$ to buy, and improve, with lots
of animated components. Just think of how useful it will be if you could
place trimmers here and there, then tweak your circuits using a mouse driven
screw driver.

Seriously (are we allowed to be serious?) I'd love to have a simulator
that let me connect sliders to parts values so I could change values
and see the transient or frequency response change in real time, like
a real-life breadboard/scope does. I figure I'd need 100x or sometimes
1000x the CPU power that I have now to make that realistic.

Better yet, a 2-D slider that lets me explore pairs of variables.

And what an exciting experience when, tweaking your circuit, you suddently
hear a nice prrshhhhh...pfff...pop, all that real time synthesized in Dolby
5.1, with a nice animated stereo view of a flame you can look at with a m$
LCD glasses.

And automatic PowerPoint presentation generation for Jim.

John