Can somebody take a peek at this circuit for me?

[Leon Heller]

"Michael Noone" <mnoone.uiuc.edu@127.0.0.1> wrote in message
news:Xns962120B4371BDmnooneuiucedu127001@216.196.97.136...

Paul Burke <paul@scazon.com> wrote in news:3aa449F675aq5U2@individual.net:

Michael Noone wrote:


Huh?

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.

Paul Burke

Well - it's a very foreign idea to me. So far in school (I'm a second year
EE) all I've been taught with FETs is how to use them as switches.

So this will work?

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

Leon
--
Leon Heller, G1HSM
http://www.geocities.com/leon_heller

 

[Michael Noone]

"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 suggest you learn to use a simulator rather than presenting
stuff that just cannot work. By using it to examine currents
and voltages for specific branches and nodes, you should be
able to discover elementary errors for yourself.

The idea is that VSS will be 400V - so the voltage divider will
divide the output by forty, thus providing negative feedback to the
op-amp.

The supply value belongs on your schematic.

I couldn't remember how to add suppy values in Eagle

There is no value on the shunt leg of your divider.
So, my prediction is it will divide by "unknown".

I marked the two voltage dividing resistors as having R and 39R ohms. I
wasn't sure what exact value to use for those - but I was thinking I'd
probabaly use resistors with values in the megaohms, so that they don't
have to dissipate too much power.

When you simulate your circuit, you will find that the
MOSFET is always on. I leave it to you to figure out
why. A "simulation" done with your mind would be
a good way to start. That is a skill you will need no
matter how good computer based simulation become.

I don't understand - say I apply a 0V signal to the input. Assuming the
mosfet is off already, vout will be ground, as the load is grounded (which
now I realize I failed to mention), and thus the voltage divider will
divide 0 by forty - and so both V+ and V- on the op-amp will be 0, and the
op-amp will be happy.

Unless there is a load, and it is connected to a more
positive level than the VSS supply, I would expect no
output like what you probably hope for.

The load would be connected to ground.

Another issue with your circuit, (and boost stages
added to op-amps generally), is that it may not
be stable. Depending on your load, your circuit
could easily oscillate (once you get the MOSFET
to not be always on).

I was most worried about stability. Now that I'm thinking about it - I
would think that this circuit will oscilate - say I give it a 5V input (to
v-). If the circuit worked like hoped eventually vout would be 200V, then
the voltage divider would divide 200 by 40, and V+ would be 5V to. Since
the op-amp amplifies the difference between V+ and V-, Vout from the op-amp
would be 0, and it would continue to oscilate back and forth like that.

Sure. Be sure to ignore the crap that gets thrown
around here. It reflects nothing upon you. You
may want to take basic questions like this to
alt.electronics.basics
where there is a little more tolerance.

That said, more care inspecting your schematics
before they leave your desk would be good.

Thanks,

-M. Noone

 

[Larry Brasfield]

"Michael Noone" <mnoone.uiuc.edu@127.0.0.1> wrote in message
news:Xns96217F7D8C823mnooneuiucedu127001@216.196.97.136...

"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in
news:YiZ%d.45$e%3.160@news.uswest.net:
"Michael Noone" <mnoone.uiuc.edu@127.0.0.1> wrote in message
news:Xns96217A2E8B647mnooneuiucedu127001@216.196.97.136...
....
OK then well now I'm just confused - how would you switch a very high
voltage signal with a mosfet with a low voltage input?

To do that in a DC coupled manner with a ground
referenced load and a ground referenced controller
normally requires at least 1 more transistor, itself
having similar HV withstand. The process of getting
a signal from one voltage range to another is often
called "translating". A common base amplifier could
do it for your application.

Could you reccomend a transistor that would be able to serve this
function? I've looked before for high voltage transistors and found very
little.

Go to www.onsemi.com and try again.

And don't call it "switch" when you mean to drive
the FET so that it has varying transconductance.

Well - actually I meant switch. Switching is the usage of mosfets that
I'm familiar with, using them to make a linear output is something I'm
not fully comfortable with just yet. I was asking in general, not about
the schematic that I posted.

In the context you used the word, it was inappropriate
and indicates, to people sharing the same language,
that you either misconceive the circuit or are not yet
familiar with what the word really means.

....

So - once a high volage transistor is used to drive the gate, what else
do I need to change to make the circuit work?

I would use this configuration:

VCC
+
.----)---.
| |
.-. .-.
| | | |
| | | |
'-' '-'
| |
| |
o-----||-+
| ||->
| ||-+
| |
| |
| o------.OUT
| | |
|| | | .-.
.-----||--. |/ | | |
| || | GND-| | | |
| | |> | '-'
___ | |\| | | | |
GND-|___|-o--|-\ | ___ | | GND
| >---o---|___|----o |
.--|+/ . |
| |/| | |
| GND-|<- |
| |
___ | ___ |
IN -|___|-o---------|___|-----------------'
(created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de)

You can set the resistors associated with the FET to
control loop gain while setting the emitter resistor
to limit the max gate drive. The response will tend
to be stable if you do not set the power amp stage
gain too high and make the integrator feedback
network pole in about the same place that the
power amp stage has its lowest frequency pole.
It inverts, so if your heart is set on the transfer
function you posted, you'll need to adjust.

I still think you need to

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

 

[John Fields]

On Tue, 22 Mar 2005 12:32:16 -0600, Michael Noone
<mnoone.uiuc.edu@127.0.0.1> wrote:

"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in
news:YiZ%d.45$e%3.160@news.uswest.net:

"Michael Noone" <mnoone.uiuc.edu@127.0.0.1> wrote in message
news:Xns96217A2E8B647mnooneuiucedu127001@216.196.97.136...
"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in
news:% TY%d.35$e%3.343@news.uswest.net:
...
Regarding circuit shown at:
https://netfiles.uiuc.edu/mnoone/www/Linearamplifierwithfet.jpg
[Why the FET dies resolved.]

OK then well now I'm just confused - how would you switch a very high
voltage signal with a mosfet with a low voltage input?

To do that in a DC coupled manner with a ground
referenced load and a ground referenced controller
normally requires at least 1 more transistor, itself
having similar HV withstand. The process of getting
a signal from one voltage range to another is often
called "translating". A common base amplifier could
do it for your application.

Could you reccomend a transistor that would be able to serve this
function? I've looked before for high voltage transistors and found very
little.

And don't call it "switch" when you mean to drive
the FET so that it has varying transconductance.

Well - actually I meant switch. Switching is the usage of mosfets that
I'm familiar with, using them to make a linear output is something I'm
not fully comfortable with just yet. I was asking in general, not about
the schematic that I posted.

I thought one of the
big ideas of fets was that you could take a small input voltage and
switch a large input voltage - but that seems to not be right?

That has not been contravened here.

Thanks,

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

So - once a high volage transistor is used to drive the gate, what else
do I need to change to make the circuit work? Best regards,

---

+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.

--
John Fields

 

[Larry Brasfield]

"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?

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

 

[Pooh Bear]

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.



Jeez ! Academics !


Graham

 

[Larry Brasfield]

Derf transform applied.

"Fred Bloggs" <nospam@nospam.com> wrote in
message news:42411186.9000502@nospam.com...

Larry Brasfield wrote:
....
You need to consider:

1. What range of output voltage (with respect to ground)
can the op-amp output cover given its connections?
2. Given the FET source connection, how does answer
to 1 affect the gate-to-source voltage applied to the FET?
3. What is the rated gate-to-source voltage of the FET?

When you have answers to those questions, you will have
the answer to "Why would it get killed?"

That's what you say but now, but your earlier post said that it would just be "always on"- so which is it?

This is fully explained in my post of 3:25 today,
where it is clear that the context is simulation.
In SPICE, components never get killed.

Here, the question on the table was "Why would
it get killed?", referring to the plain circuit.
In real circuits, components can die.

Is that really so hard to understand for one of
the greatest electronic intellects on Earth?

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

 

[John Fields]

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"
--
John Fields

 

[John Fields]

On Wed, 23 Mar 2005 15:04:48 -0800, "Larry Brasfield"
<donotspam_larry_brasfield@hotmail.com> wrote:

"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.

---
ISTR that in my earliest post claiming that the cap was there to keep
the circuit from oscillating, your retort was that I was wrong
because, no matter what value of capacitance was placed there, the
circuit would not oscillate. I believe there's adequate documentation
to prove that such was the case and, if you choose to dispute it, I'm
sure that Fred can provide the timeline if he chooses to. ISTM that
that's a lot of work though, and hardly worth the effort, since we all
know that YFOS.
---

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.

---
So what are you trying to say? That you knew my circuit was going to
oscillate before I did? OK, I don't have a problem with that, but
what I _would_ like you to explain is how you could claim that, early
on, my circuit was incapable of oscillating, regardless of the the
value of shunt C on the input of the opamp.
---

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.

---
And yet you refuse to proffer the analysis on the basis that the
circuit isn't worthy of analysis? Quite circular and self-serving,
I'd say.
---

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.

---
Yes, I'm sure they are. You're brought to task and must demur with
weighty excuses which are hard to carry.
---

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?

---
Not at all. The "If frogs had wings" thing was made with respect to
the idiotic suggestion that the circuit could _intentonally_ be used
as a VCO. On second thought, though, that 400V range might be able to
be used to provide a really wide range VCO. Might be worth looking
into...
---

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?

---
Writing a book?
---

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".

---
And yet, you chose to complain about those values not being there and
offered your circuit as a better solution, undressed as well.
---

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?

---
Experience
---

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.

---
it sounds to me like you're saying that you made an error but it
wasn't really your fault because...

Did you make an error or not? Yes or no.
---

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.

---
Hey, _you're_ the one saying that simulations are suspect because of
this and that, and I'm agreeing with you because it's convenient for
me to go along with you. If I'm wrong, prove it by showing that
simulations are always accurate and that you ran it right.
---

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.

---
You're a fucking idiot. If you've got a 400V source and it has to go
through a pass transistor into a load which is looking for 400V, how
do you propose to make the pass transistor lossless?

I should have known better than this, dammit, playing with another
fucking troll. Aaaarrghhhh!!!
---

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".

---
Fuck you and all of your bullshit rhetoric, loser, if you can't
understand the simple concept of headroom you need to start practicing
saying: "Do you want fries with that?"

--
John Fields

 

[Michael Noone]

John Larkin <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote in
news:8mf441lqe4rg6qo6tt5c5ubsrknkthed0n@4ax.com:

Hey, Michael, I posted it again. This uses the V+ and V- power supply
currents of the opamp to drive the led sides of high-voltage
optocouplers. I use a variant of this in a box I built for some guys
who make electron-microscope sorta things, where not much current is
needed. But 20 mA is probably pushing this too hard... the opto ctr's
are low, and the couplers could well fry from power dissipation.

But the general idea of using optocouplers as analog level shifters is
sorta handy to keep around. We did discuss cascoding lower-voltage
optos with depletion-mode mosfets.

Is the fluid one of those electro-rheological thingies?

John

Very interesting circuit! In reality current should be in the 1ma-5ma

range, do you think it could handle that? Or would it be possible to
somehow wire the couplers in parallel? Thanks,

-Michael

 

[Michael Noone]

John Fields <jfields@austininstruments.com> wrote in
news:43k341drdd6heiomm151a6cq159mvd1qnu@4ax.com:

Sure. I'd be happy too. Matter of fact, since it's just text I'll go
ahead and paste it in here:


Version 4
SHEET 1 1052 680
WIRE -192 240 -192 0
WIRE -192 432 -192 320
WIRE -192 496 -192 432
WIRE -16 0 -192 0
WIRE -16 16 -16 0
WIRE -16 112 -16 96
WIRE 48 0 -16 0
WIRE 128 112 -16 112
WIRE 128 112 128 48
WIRE 128 192 128 112
WIRE 128 432 -192 432
WIRE 128 432 128 288
WIRE 208 272 176 272
WIRE 320 272 288 272
WIRE 320 272 320 192
WIRE 352 272 320 272
WIRE 384 240 384 144
WIRE 384 432 128 432
WIRE 384 432 384 304
WIRE 416 192 320 192
WIRE 512 0 144 0
WIRE 512 32 512 0
WIRE 512 288 416 288
WIRE 512 288 512 112
WIRE 512 320 512 288
WIRE 512 432 384 432
WIRE 512 432 512 400
WIRE 560 192 480 192
WIRE 560 256 416 256
WIRE 560 256 560 192
WIRE 592 256 560 256
WIRE 880 256 672 256
WIRE 880 288 880 256
WIRE 880 432 512 432
WIRE 880 432 880 368
WIRE 992 144 384 144
WIRE 992 288 992 144
WIRE 992 432 880 432
WIRE 992 432 992 368
FLAG -192 496 0
SYMBOL voltage -192 224 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 300
SYMBOL res -32 0 R0
SYMATTR InstName R1
SYMATTR Value 1e6
SYMBOL res 304 256 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R2
SYMATTR Value 1000
SYMBOL Opamps\\UniversalOpamp 384 272 M0
SYMATTR InstName U1
SYMBOL res 496 16 R0
SYMATTR InstName R3
SYMATTR Value 1e6
SYMBOL res 496 304 R0
SYMATTR InstName R4
SYMATTR Value 34483
SYMBOL voltage 992 272 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 12
SYMBOL voltage 880 272 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 10
SYMBOL nmos 176 192 M0
SYMATTR InstName M1
SYMATTR Value IXFX90N30
SYMBOL nmos 48 48 R270
SYMATTR InstName M2
SYMATTR Value IXFX90N30
SYMBOL res 688 240 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 38 55 VTop 0
SYMATTR InstName R5
SYMATTR Value 10k
SYMBOL cap 480 176 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C1
SYMATTR Value .1e-6
TEXT -226 520 Left 0 !.tran 0 .1s 0s .1s

Hi again Mr. Fields - I'm afraid I'm not very sure how to interpret
this. I think this is input for spice? Could you reccomend a free
version of spice (for windows) that could interepret this? Thanks again,

-Michael Noone

 

[John Larkin]

On Fri, 25 Mar 2005 14:39:03 -0600, Michael Noone
<mnoone.uiuc.edu@127.0.0.1> wrote:

John Fields <jfields@austininstruments.com> wrote in
news:43k341drdd6heiomm151a6cq159mvd1qnu@4ax.com:
Sure. I'd be happy too. Matter of fact, since it's just text I'll go
ahead and paste it in here:


Version 4
SHEET 1 1052 680
WIRE -192 240 -192 0
WIRE -192 432 -192 320
WIRE -192 496 -192 432
WIRE -16 0 -192 0
WIRE -16 16 -16 0
WIRE -16 112 -16 96
WIRE 48 0 -16 0
WIRE 128 112 -16 112
WIRE 128 112 128 48
WIRE 128 192 128 112
WIRE 128 432 -192 432
WIRE 128 432 128 288
WIRE 208 272 176 272
WIRE 320 272 288 272
WIRE 320 272 320 192
WIRE 352 272 320 272
WIRE 384 240 384 144
WIRE 384 432 128 432
WIRE 384 432 384 304
WIRE 416 192 320 192
WIRE 512 0 144 0
WIRE 512 32 512 0
WIRE 512 288 416 288
WIRE 512 288 512 112
WIRE 512 320 512 288
WIRE 512 432 384 432
WIRE 512 432 512 400
WIRE 560 192 480 192
WIRE 560 256 416 256
WIRE 560 256 560 192
WIRE 592 256 560 256
WIRE 880 256 672 256
WIRE 880 288 880 256
WIRE 880 432 512 432
WIRE 880 432 880 368
WIRE 992 144 384 144
WIRE 992 288 992 144
WIRE 992 432 880 432
WIRE 992 432 992 368
FLAG -192 496 0
SYMBOL voltage -192 224 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 300
SYMBOL res -32 0 R0
SYMATTR InstName R1
SYMATTR Value 1e6
SYMBOL res 304 256 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R2
SYMATTR Value 1000
SYMBOL Opamps\\UniversalOpamp 384 272 M0
SYMATTR InstName U1
SYMBOL res 496 16 R0
SYMATTR InstName R3
SYMATTR Value 1e6
SYMBOL res 496 304 R0
SYMATTR InstName R4
SYMATTR Value 34483
SYMBOL voltage 992 272 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 12
SYMBOL voltage 880 272 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 10
SYMBOL nmos 176 192 M0
SYMATTR InstName M1
SYMATTR Value IXFX90N30
SYMBOL nmos 48 48 R270
SYMATTR InstName M2
SYMATTR Value IXFX90N30
SYMBOL res 688 240 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 38 55 VTop 0
SYMATTR InstName R5
SYMATTR Value 10k
SYMBOL cap 480 176 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C1
SYMATTR Value .1e-6
TEXT -226 520 Left 0 !.tran 0 .1s 0s .1s

Hi again Mr. Fields - I'm afraid I'm not very sure how to interpret
this. I think this is input for spice? Could you reccomend a free
version of spice (for windows) that could interepret this? Thanks again,

-Michael Noone

Michael,

Download the free SwitcherCad/LTSpice from Linear Technology.

Highlight and right-click copy the text from JFs post.

Open Notepad, paste, save as FRIDAY.ASC somewhere.

Open Switchercad and File/Open FRIDAY.ASC

You should see the schematic and be able to simulate it.

John

 

[John Larkin]

On Fri, 25 Mar 2005 14:35:34 -0600, Michael Noone
<mnoone.uiuc.edu@127.0.0.1> wrote:

John Larkin <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote in
news:8mf441lqe4rg6qo6tt5c5ubsrknkthed0n@4ax.com:

Hey, Michael, I posted it again. This uses the V+ and V- power supply
currents of the opamp to drive the led sides of high-voltage
optocouplers. I use a variant of this in a box I built for some guys
who make electron-microscope sorta things, where not much current is
needed. But 20 mA is probably pushing this too hard... the opto ctr's
are low, and the couplers could well fry from power dissipation.

But the general idea of using optocouplers as analog level shifters is
sorta handy to keep around. We did discuss cascoding lower-voltage
optos with depletion-mode mosfets.

Is the fluid one of those electro-rheological thingies?

John

Very interesting circuit! In reality current should be in the 1ma-5ma
range, do you think it could handle that? Or would it be possible to
somehow wire the couplers in parallel? Thanks,

Hmmm, yes. Wire the LEDs in series and the phototransistors in
parallel. Use more than +-5 for the opamp supplies to make up for the
LED voltage drop. Idle power dissipation could be an issue here.

Take a look at the datasheet for the optocoupler to see how hard it
could be safely pushed. I think they want a b-e resistor at high
voltages, too.

I bet there's a way to stack the phototransistors for more than 400
volts swing!

John

 

[Michael Noone]

John Fields <jfields@austininstruments.com> wrote in
news90941le00n0bbhdhds5fhr33fcrijqka9@4ax.com:

Go to

http://www.linear-tech.com/designtools/softwareRegistration.jsp

and download their free simulator, then cut and paste the text file I
posted in its entirety into some convenient directory, rename it with
a .asc suffix and open it with the simulator.

Great - that opened it up perfectly. But now, I must admit I'm still a bit
lost. Is V3 the input? What is the output? And might you be able to
reccomend a guide to how to simulate circuits with this program?

Thanks again for all your help and putting up with my questions,

-Michael Noone

 

[Robert Monsen]

Michael Noone wrote:

John Fields <jfields@austininstruments.com> wrote in
news90941le00n0bbhdhds5fhr33fcrijqka9@4ax.com:

Go to

http://www.linear-tech.com/designtools/softwareRegistration.jsp

and download their free simulator, then cut and paste the text file I
posted in its entirety into some convenient directory, rename it with
a .asc suffix and open it with the simulator.


Great - that opened it up perfectly. But now, I must admit I'm still a bit
lost. Is V3 the input? What is the output? And might you be able to
reccomend a guide to how to simulate circuits with this program?

Thanks again for all your help and putting up with my questions,

-Michael Noone

Yes, V3 is the control voltage. To simulate the circuit, you just click
on the little running man, or go to the simulate menu and select run.

You can set up the voltage source V3 to simulate going from 0 to 10 to
see what the circuit does. Right click on the '.tran' statement in the
schematic, and select DC Sweep. Type V3 in as the name of the source,
select linear sweep, from 0 to 10, increment 0.1. Then, click on the
running man again.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

 

[Michael Noone]

Robert Monsen <rcsurname@comcast.net> wrote in
news:3L2dnXJnPpNx9NvfRVn-sg@comcast.com:

Michael Noone wrote:
John Fields <jfields@austininstruments.com> wrote in
news90941le00n0bbhdhds5fhr33fcrijqka9@4ax.com:

Go to

http://www.linear-tech.com/designtools/softwareRegistration.jsp

and download their free simulator, then cut and paste the text file
I posted in its entirety into some convenient directory, rename it
with a .asc suffix and open it with the simulator.


Great - that opened it up perfectly. But now, I must admit I'm still
a bit lost. Is V3 the input? What is the output? And might you be
able to reccomend a guide to how to simulate circuits with this
program?

Thanks again for all your help and putting up with my questions,

-Michael Noone

Yes, V3 is the control voltage. To simulate the circuit, you just
click on the little running man, or go to the simulate menu and select
run.

You can set up the voltage source V3 to simulate going from 0 to 10 to
see what the circuit does. Right click on the '.tran' statement in the
schematic, and select DC Sweep. Type V3 in as the name of the source,
select linear sweep, from 0 to 10, increment 0.1. Then, click on the
running man again.

OK great - but now what is the output? Is the output node 6? (coming
from mosfet 2)

Thanks again,

-Michael

 

[John Fields]

On Sun, 27 Mar 2005 10:10:43 -0600, Michael Noone
<mnoone.uiuc.edu@127.0.0.1> wrote:

Robert Monsen <rcsurname@comcast.net> wrote in
news:3L2dnXJnPpNx9NvfRVn-sg@comcast.com:

Michael Noone wrote:
John Fields <jfields@austininstruments.com> wrote in
news90941le00n0bbhdhds5fhr33fcrijqka9@4ax.com:

Go to

http://www.linear-tech.com/designtools/softwareRegistration.jsp

and download their free simulator, then cut and paste the text file
I posted in its entirety into some convenient directory, rename it
with a .asc suffix and open it with the simulator.


Great - that opened it up perfectly. But now, I must admit I'm still
a bit lost. Is V3 the input? What is the output? And might you be
able to reccomend a guide to how to simulate circuits with this
program?

Thanks again for all your help and putting up with my questions,

-Michael Noone

Yes, V3 is the control voltage. To simulate the circuit, you just
click on the little running man, or go to the simulate menu and select
run.

You can set up the voltage source V3 to simulate going from 0 to 10 to
see what the circuit does. Right click on the '.tran' statement in the
schematic, and select DC Sweep. Type V3 in as the name of the source,
select linear sweep, from 0 to 10, increment 0.1. Then, click on the
running man again.


OK great - but now what is the output? Is the output node 6? (coming
from mosfet 2)

---
Yes.

--
John Fields

 

[Genome]

"Michael Noone" <mnoone.uiuc.edu@127.0.0.1> wrote in message
news:Xns9626677EE5083mnooneuiucedu127001@216.196.97.136...

OK great - but now what is the output? Is the output node 6? (coming
from mosfet 2)

Thanks again,

-Michael

If you look at the toolshed then you get the opportunity to stick a
label on things.

Then you get to pick it in your wish list.

In the same way that you deliberately fucked up your conceptions of
the piece of shit you generated earlier you will not care to notice
that the label can be set up to be an input or output or
bi-directional port.

http://www.uiuc.edu/index.html

You're giving Illinois a bad name

DNA

My e-mail address is valid.

 

[Larry Brasfield]

"Michael Noone" <mnoone.uiuc.edu@127.0.0.1> wrote in message
news:Xns96217A2E8B647mnooneuiucedu127001@216.196.97.136...

"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in news:%
TY%d.35$e%3.343@news.uswest.net:
....

Regarding circuit shown at:
https://netfiles.uiuc.edu/mnoone/www/Linearamplifierwithfet.jpg
[Why the FET dies resolved.]

OK then well now I'm just confused - how would you switch a very high
voltage signal with a mosfet with a low voltage input?

To do that in a DC coupled manner with a ground
referenced load and a ground referenced controller
normally requires at least 1 more transistor, itself
having similar HV withstand. The process of getting
a signal from one voltage range to another is often
called "translating". A common base amplifier could
do it for your application.

And don't call it "switch" when you mean to drive
the FET so that it has varying transconductance.

I thought one of the
big ideas of fets was that you could take a small input voltage and switch
a large input voltage - but that seems to not be right?

That has not been contravened here.

Thanks,

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

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

 

[John Woodgate]

I read in sci.electronics.design that Jim Thompson
<thegreatone@example.com> wrote (in
<7jn5411prqkhmp22bo07q4vo6h50pq4fo5@4ax.com&gt about 'Can somebody take a
peek at this circuit for me?', on Thu, 24 Mar 2005:

To do a PowerPoint-like presentation in Adobe Acrobat requires using
"fields", show destinations, scan and name pages; and takes this
_complex_ JavaScript....

gotoNamedDest("PageName")

;-)

Exactly! (;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk