Op Amp Calculations

[Terry Given]

Rich Grise wrote...



PIMP?

Pee In My Pants....

Cheers
Terry

 

[Terry Given]

Jim Thompson wrote:


Fred Bartoli wrote:


"Terry Given" <[email protected]> a écrit dans le message de


Fred Bloggs wrote:


Terry Given wrote:


What about the typo? the 2nd transistor shorts out the +5V supply....

shouldnt there be something to limit current though? +5V...Vce...Vbe
with nary a resistor in sight. ultimately the base current could be as
high as the opamp output current (assuming negligible contribution from
the summing junction)....

[snip]


Not quite, essentially all the incremental base drive voltage is
developed across hie of the first transistor. Your reasoning is wrong
and your estimate is high.

"hie"... what BS! Fred must be of the "Kevin School" of transistor
operation ;-)



And it STILL will go up in flames during power-up. Sheeesh! Such
DESIGN ;-)

[snip]

...Jim Thompson

Hi Jim,

can you please elaborate on why? I presume because of the 2nd transistor....

Cheers
Terry


No limit on IB of 1st transistor except output capability of OpAmp

IC of 1st transistor IS limited somewhat by FB resistors, but
substantial IB is introduced into 2nd transistor

Absolutely nothing to limit IC of 2nd transistor except current
crowding

My best guess is that all three transistors will flame or be seriously
damaged when Murphy chooses ;-)

(And the bandwidth will be nothing like claimed.)

What was the original intent (OP)? I didn't get in on this thread at
the beginning.

...Jim Thompson

This is not rocket science- we already said that the second transistor C
should be tied to the CE collector. If you're worried by the OA dumping
excessive current into the base then put a 560 in series with its output.

That's still insufficient. Good engineering practice would limit base
drive from the OpAmp AND also the collector current of the 2nd
transistor.

...Jim Thompson

Thanks Jim, thats pretty much what I figured. Its like driving, really.
any fool can drive on a straight, flat road with no traffic and good
visibility. Going round a corner sideways in the pouring rain, with a
logging truck coming towards you, sorts the men from the boys.

Cheers
Terry

 

[Jim Thompson]

[snip]

That's still insufficient. Good engineering practice would limit base
drive from the OpAmp AND also the collector current of the 2nd
transistor.

...Jim Thompson

Thanks Jim, thats pretty much what I figured. Its like driving, really.
any fool can drive on a straight, flat road with no traffic and good
visibility. Going round a corner sideways in the pouring rain, with a
logging truck coming towards you, sorts the men from the boys.

Cheers
Terry

I did that once on snow. Nothing like sliding sideways, down a hill
yet, and dodging traffic, to put some "age" on you ;-)

...Jim Thompson

 

[Rich Grise]

[snip]

That's still insufficient. Good engineering practice would limit base
drive from the OpAmp AND also the collector current of the 2nd
transistor.

...Jim Thompson

Thanks Jim, thats pretty much what I figured. Its like driving, really.
any fool can drive on a straight, flat road with no traffic and good
visibility. Going round a corner sideways in the pouring rain, with a
logging truck coming towards you, sorts the men from the boys.

Cheers
Terry

I did that once on snow. Nothing like sliding sideways, down a hill
yet, and dodging traffic, to put some "age" on you ;-)

Ever tried fishtailing on the freeway at 55MPH on black ice? That's
kind of a rush too. ;-)

Cheers!
Rich

 

[Jim Thompson]

Jim Thompson wrote:
[snip]

That's still insufficient. Good engineering practice would limit base
drive from the OpAmp AND also the collector current of the 2nd
transistor.

...Jim Thompson

Thanks Jim, thats pretty much what I figured. Its like driving, really.
any fool can drive on a straight, flat road with no traffic and good
visibility. Going round a corner sideways in the pouring rain, with a
logging truck coming towards you, sorts the men from the boys.

Cheers
Terry

I did that once on snow. Nothing like sliding sideways, down a hill
yet, and dodging traffic, to put some "age" on you ;-)

Ever tried fishtailing on the freeway at 55MPH on black ice? That's
kind of a rush too. ;-)

Cheers!
Rich

I drove the Pennsylvania Turnpike from west-end-to-east-end one time
with an eery feeling of never quite touching the ground ;-)

...Jim Thompson

 

[Winfield Hill]

Terry Given wrote...

Pee In My Pants....

Aawwaarrkk!!

 

[Winfield Hill]

Jim Thompson wrote...

I drove the Pennsylvania Turnpike from west-end-to-east-end one
time with an eery feeling of never quite touching the ground ;-)

When one drives all the way across the country at one go,
one gets that feeling at various points.

 

[Keith Williams]

Jim Thompson wrote:
[snip]

That's still insufficient. Good engineering practice would limit base
drive from the OpAmp AND also the collector current of the 2nd
transistor.

...Jim Thompson

Thanks Jim, thats pretty much what I figured. Its like driving, really.
any fool can drive on a straight, flat road with no traffic and good
visibility. Going round a corner sideways in the pouring rain, with a
logging truck coming towards you, sorts the men from the boys.

Cheers
Terry

I did that once on snow. Nothing like sliding sideways, down a hill
yet, and dodging traffic, to put some "age" on you ;-)

Ever tried fishtailing on the freeway at 55MPH on black ice? That's
kind of a rush too. ;-)

Cheers!
Rich

I drove the Pennsylvania Turnpike from west-end-to-east-end one time
with an eery feeling of never quite touching the ground ;-)

I drove I80 W->E across PA on about an inch of ice one time. It was raining
and freezing so fast that I had to put the defroster on high enough that I had
to open the windows so my hair wouldn't catch fire. ;-) We finally broke free
of the storm around Stroudsburg after 10 hours of white-knuckle driving. We
only had about three hours driving time to get home but the wife said, no
(*she* was too tired)! We stayed the night in a hotel, only to fight the storm
again the next day. :-(

 

[Jim Thompson]

On Thu, 06 Oct 2005 13:08:07 -0700, Jim Thompson wrote:

Jim Thompson wrote:
[snip]

That's still insufficient. Good engineering practice would limit base
drive from the OpAmp AND also the collector current of the 2nd
transistor.

...Jim Thompson

Thanks Jim, thats pretty much what I figured. Its like driving, really.
any fool can drive on a straight, flat road with no traffic and good
visibility. Going round a corner sideways in the pouring rain, with a
logging truck coming towards you, sorts the men from the boys.

Cheers
Terry

I did that once on snow. Nothing like sliding sideways, down a hill
yet, and dodging traffic, to put some "age" on you ;-)

Ever tried fishtailing on the freeway at 55MPH on black ice? That's
kind of a rush too. ;-)

Cheers!
Rich

I drove the Pennsylvania Turnpike from west-end-to-east-end one time
with an eery feeling of never quite touching the ground ;-)

I drove I80 W->E across PA on about an inch of ice one time. It was raining
and freezing so fast that I had to put the defroster on high enough that I had
to open the windows so my hair wouldn't catch fire. ;-) We finally broke free
of the storm around Stroudsburg after 10 hours of white-knuckle driving. We
only had about three hours driving time to get home but the wife said, no
(*she* was too tired)! We stayed the night in a hotel, only to fight the storm
again the next day. :-(

Well, if we're going to play "Can you top that" ;-)

Drove across Oklahoma one winter in so much cold rain that I had to
defrost using the air conditioning :-(

...Jim Thompson

 

[Keith Williams]

On Thu, 06 Oct 2005 13:08:07 -0700, Jim Thompson wrote:

Jim Thompson wrote:
[snip]

That's still insufficient. Good engineering practice would limit base
drive from the OpAmp AND also the collector current of the 2nd
transistor.

...Jim Thompson

Thanks Jim, thats pretty much what I figured. Its like driving, really.
any fool can drive on a straight, flat road with no traffic and good
visibility. Going round a corner sideways in the pouring rain, with a
logging truck coming towards you, sorts the men from the boys.

Cheers
Terry

I did that once on snow. Nothing like sliding sideways, down a hill
yet, and dodging traffic, to put some "age" on you ;-)

Ever tried fishtailing on the freeway at 55MPH on black ice? That's
kind of a rush too. ;-)

Cheers!
Rich


I drove the Pennsylvania Turnpike from west-end-to-east-end one time
with an eery feeling of never quite touching the ground ;-)

I drove I80 W->E across PA on about an inch of ice one time. It was raining
and freezing so fast that I had to put the defroster on high enough that I had
to open the windows so my hair wouldn't catch fire. ;-) We finally broke free
of the storm around Stroudsburg after 10 hours of white-knuckle driving. We
only had about three hours driving time to get home but the wife said, no
(*she* was too tired)! We stayed the night in a hotel, only to fight the storm
again the next day. :-(

Well, if we're going to play "Can you top that" ;-)

Oh, yeah!

Drove across Oklahoma one winter in so much cold rain that I had to
defrost using the air conditioning :-(

You had an Oklahoma?! Wait...

(The AC in my truck is on whenever the defroster is on)

 

[Jim Thompson]

On Thu, 06 Oct 2005 13:08:07 -0700, Jim Thompson wrote:

Jim Thompson wrote:
[snip]

That's still insufficient. Good engineering practice would limit base
drive from the OpAmp AND also the collector current of the 2nd
transistor.

...Jim Thompson

Thanks Jim, thats pretty much what I figured. Its like driving, really.
any fool can drive on a straight, flat road with no traffic and good
visibility. Going round a corner sideways in the pouring rain, with a
logging truck coming towards you, sorts the men from the boys.

Cheers
Terry

I did that once on snow. Nothing like sliding sideways, down a hill
yet, and dodging traffic, to put some "age" on you ;-)

Ever tried fishtailing on the freeway at 55MPH on black ice? That's
kind of a rush too. ;-)

Cheers!
Rich


I drove the Pennsylvania Turnpike from west-end-to-east-end one time
with an eery feeling of never quite touching the ground ;-)

I drove I80 W->E across PA on about an inch of ice one time. It was raining
and freezing so fast that I had to put the defroster on high enough that I had
to open the windows so my hair wouldn't catch fire. ;-) We finally broke free
of the storm around Stroudsburg after 10 hours of white-knuckle driving. We
only had about three hours driving time to get home but the wife said, no
(*she* was too tired)! We stayed the night in a hotel, only to fight the storm
again the next day. :-(

Well, if we're going to play "Can you top that" ;-)

Oh, yeah!

Drove across Oklahoma one winter in so much cold rain that I had to
defrost using the air conditioning :-(

You had an Oklahoma?! Wait...

(The AC in my truck is on whenever the defroster is on)

Newer vehicles have that feature... this was in 1964, when A/C was
still pretty much "add-on".

...Jim Thompson

 

[keith]

On Thu, 06 Oct 2005 13:08:07 -0700, Jim Thompson wrote:

Jim Thompson wrote:
[snip]

That's still insufficient. Good engineering practice would limit base
drive from the OpAmp AND also the collector current of the 2nd
transistor.

...Jim Thompson

Thanks Jim, thats pretty much what I figured. Its like driving, really.
any fool can drive on a straight, flat road with no traffic and good
visibility. Going round a corner sideways in the pouring rain, with a
logging truck coming towards you, sorts the men from the boys.

Cheers
Terry

I did that once on snow. Nothing like sliding sideways, down a hill
yet, and dodging traffic, to put some "age" on you ;-)

Ever tried fishtailing on the freeway at 55MPH on black ice? That's
kind of a rush too. ;-)

Cheers!
Rich


I drove the Pennsylvania Turnpike from west-end-to-east-end one time
with an eery feeling of never quite touching the ground ;-)

I drove I80 W->E across PA on about an inch of ice one time. It was raining
and freezing so fast that I had to put the defroster on high enough that I had
to open the windows so my hair wouldn't catch fire. ;-) We finally broke free
of the storm around Stroudsburg after 10 hours of white-knuckle driving. We
only had about three hours driving time to get home but the wife said, no
(*she* was too tired)! We stayed the night in a hotel, only to fight the storm
again the next day. :-(

Well, if we're going to play "Can you top that" ;-)

Oh, yeah!

Drove across Oklahoma one winter in so much cold rain that I had to
defrost using the air conditioning :-(

You had an Oklahoma?! Wait...

(The AC in my truck is on whenever the defroster is on)

Newer vehicles have that feature...

You misspelled "feechur". Forcing one to run the compressor when
using the defroster is nutz!

this was in 1964, when A/C was still pretty much "add-on".

Had AC been invented? ;-) I learned to drive on a '64 Ford Custom (in
'68), no AC, no auto, no power (brake or steering). I bought a similar
car in '78. A (then) new Ford Granada ESS (also no AC, auto, or power);
great car! No one would believe there was ever an ESS with a stick. ;-)

 

[Jim Thompson]

On Fri, 07 Oct 2005 12:51:14 -0700, Jim Thompson wrote:
[snip]

this was in 1964, when A/C was still pretty much "add-on".

Had AC been invented? ;-) I learned to drive on a '64 Ford Custom (in
'68), no AC, no auto, no power (brake or steering). I bought a similar
car in '78. A (then) new Ford Granada ESS (also no AC, auto, or power);
great car! No one would believe there was ever an ESS with a stick. ;-)

I learned to drive in a '56 Mercury station wagon, in '56 ;-) The
power steering failed as I was trying to pass "parallel" parking. I
managed to get it in the space anyway ;-)

...Jim Thompson

 

[Rich Grise]

Jim Thompson wrote...

When one drives all the way across the country at one go,
one gets that feeling at various points.

I think the weirdest driving experience I've ever had was the summer
between 11th and 12th grades. I had a "summer job": part time
busboy/dishwasher. The commute was about 10 miles, on Highway 12, which
has since been replaced by I-94. (Wayzata to St. Louis Park, MN.) Anyway,
it was a really really boring drive. I had heard about "highway hypnosis",
and all that safety stuff they try to indoctrinate kids with. Anyway, One
time, I got off work, jumped in the car, headed down the highway, and the
next thing I noticed, I was already home. And this was before I drank,
smoked, or smoked! (but I was 16, so could have been a victim of
testosterone poisoning. ;-) )

(the point was, there was about 10 minutes of commute time that I
completely spaced out on and didn't even remember driving. If I'd
crashed, it would have been my fault. I guess that's when I decided,
"In the car, be on Red Alert at all times!")

Cheers!
Rich

 

[Rich Grise]

On Thu, 06 Oct 2005 13:08:07 -0700, Jim Thompson wrote:

Jim Thompson wrote:
[snip]

That's still insufficient. Good engineering practice would limit base
drive from the OpAmp AND also the collector current of the 2nd
transistor.

...Jim Thompson

Thanks Jim, thats pretty much what I figured. Its like driving, really.
any fool can drive on a straight, flat road with no traffic and good
visibility. Going round a corner sideways in the pouring rain, with a
logging truck coming towards you, sorts the men from the boys.

Cheers
Terry

I did that once on snow. Nothing like sliding sideways, down a hill
yet, and dodging traffic, to put some "age" on you ;-)

Ever tried fishtailing on the freeway at 55MPH on black ice? That's
kind of a rush too. ;-)

Cheers!
Rich


I drove the Pennsylvania Turnpike from west-end-to-east-end one time
with an eery feeling of never quite touching the ground ;-)

I drove I80 W->E across PA on about an inch of ice one time. It was raining
and freezing so fast that I had to put the defroster on high enough that I had
to open the windows so my hair wouldn't catch fire. ;-) We finally broke free
of the storm around Stroudsburg after 10 hours of white-knuckle driving. We
only had about three hours driving time to get home but the wife said, no
(*she* was too tired)! We stayed the night in a hotel, only to fight the storm
again the next day. :-(

Well, if we're going to play "Can you top that" ;-)

Drove across Oklahoma one winter in so much cold rain that I had to
defrost using the air conditioning :-(

...Jim Thompson

Oklahoma, hm? OK, one time driving from So. Cal. to Minnesota, while
passing through the OK/TX panhandle, there was a dust storm. Visibility
was about 100 feet. On the right side of the highway, I spotted a cinder-
block building with "COLD BEER" painted on the side in 8' high letters.
So I stopped. I mentioned "Gee, I've been snowed in before, but this
is the first time I've ever been dusted in" or some such clever thing.
The bartender said, "Welcome to fuckin' Oklahoma."

Sometimes, being snowed in isn't all that bad of a deal. ;-)

Or, if you like cold, there was the time my thermostat got stuck (in MN)
and snow was coming out the vents, until the radiator hose popped.

Cheers!
Rich

 

[keith]

On Fri, 07 Oct 2005 12:51:14 -0700, Jim Thompson wrote:
[snip]

this was in 1964, when A/C was still pretty much "add-on".

Had AC been invented? ;-) I learned to drive on a '64 Ford Custom (in
'68), no AC, no auto, no power (brake or steering). I bought a similar
car in '78. A (then) new Ford Granada ESS (also no AC, auto, or power);
great car! No one would believe there was ever an ESS with a stick. ;-)

I learned to drive in a '56 Mercury station wagon, in '56 ;-) The
power steering failed as I was trying to pass "parallel" parking. I
managed to get it in the space anyway ;-)

The examiner was so impressed that I could drive the '64 tank that he let
me parallel park where there were no cars. Even then I shifted into
the wrong gear (missed reverse - into second), but I don't think he
noticed and I didn't make the correction. ;-) He took a couple of points
off for crossing the center line on a turnabout (impossible to do
otherwise with that car, on that street/driveway), where others were
failed the same mistake.

My son had it "easy" though. He took his test in my '93 Eagle Vision TSi
(power everything, 300HP - don't stick the foot in the gas . During the
road test the #1 plug wire decided to open[*]. The examiner asked if
there was something wrong (a mechanical failure was an automatic fail).
The kid said that he didn't notice anything and continued on.

[*]That car threw the #1 wire once a year. They were a PITA to replace
with garages charging up to three hours labor. I got it down to 45min.
The last time it happened I figured out why. The specs printed on the
engine called for a spark gap of .062". The shop manual called for .035".

 

[Winfield Hill]

keith wrote...

The specs printed on the engine called for a spark gap
of .062". The shop manual called for .035".

Split the difference?

 

[Jim Thompson]

On Fri, 07 Oct 2005 18:43:09 -0700, Jim Thompson wrote:
[snip]

I learned to drive in a '56 Mercury station wagon, in '56 ;-) The
power steering failed as I was trying to pass "parallel" parking. I
managed to get it in the space anyway ;-)

[snip]

[*]That car threw the #1 wire once a year. They were a PITA to replace
with garages charging up to three hours labor. I got it down to 45min.
The last time it happened I figured out why. The specs printed on the
engine called for a spark gap of .062". The shop manual called for .035".

..062" Gack! I don't think my feeler gauges even go that high ;-)

...Jim Thompson

 

[RST Engineering \(jw\)]

Use a piece of old PCB material?

Jim

 

[DaveM]

Use a piece of old PCB material?

Jim

I use drill bits as feeler gauges when I don't have the proper gauge handy
(which is often). I have a set of metric, inch, numbered and letter bits;
with those bits, I can gauge just about any size imaginable. And I
sometimes actually use the bits to make holes... make them do double duty
{;>) The solid end of the bits are very close tolerance too.. probably
closer than many feeler gauge sets.

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!