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basic opamp grounding question

P

panfilero

Jan 1, 1970
0
Hello,

If I have an OpAmp (a 741 for example) and I want to use it as a
buffer, and will be sending it 2Vdc, and am powering it with a dual
power supply +/-10V.... do I have to tie the grounds of my input
signal to the grounds of my power supply signal? the 2V ground and
the +/-10V ground?

much thanks!
 
J

Jamie

Jan 1, 1970
0
panfilero said:
Hello,

If I have an OpAmp (a 741 for example) and I want to use it as a
buffer, and will be sending it 2Vdc, and am powering it with a dual
power supply +/-10V.... do I have to tie the grounds of my input
signal to the grounds of my power supply signal? the 2V ground and
the +/-10V ground?

much thanks!
Yes.
The only acception to the rule is if you had some form of isolation
device. In the case of the isolation, you only used the ground/common of
the input of the isolator device, it's output common does not come in
contact with the input common how ever, the output common still needs to
be connected with the circuits ground/common.

http://webpages.charter.net/jamie_5"
 
K

krw

Jan 1, 1970
0
Not directly, anyway. If the amplifier is set up as a differential
amplifier with unity gain. The output signal will be referenced to
the power supply grounds. In this configuration, the inputs ('+'
input, actually - the '-' input is along for the ride) must remain
within the common mode operating range of the Op-Amp though.

___ ___
+------|___|---+----|___|-+
| R | R |
| | |
/-\ | |\| |
( )2V +----+-\ |
\+/ Vin ___ | >--+------- +2V
+-----+|___|---+----| / out
R | |/|
|
.-.
| |R
| |
'-'
|
GND

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


Yes.
Nope.

The only acception to the rule is if you had some form of isolation
device. In the case of the isolation, you only used the ground/common of
the input of the isolator device, it's output common does not come in
contact with the input common how ever, the output common still needs to
be connected with the circuits ground/common.

http://webpages.charter.net/jamie_5"

As usual for Jamie, wrong. The resistors will be the "isolation"
devices (not to be confused with safety isolation).
 
W

whit3rd

Jan 1, 1970
0
Hello,

If I have an OpAmp (a 741 for example) and I want to use it as a
buffer, and will be sending it 2Vdc, and am powering it with a dual
power supply +/-10V.... do I have to tie the grounds of my input
signal to the grounds of my power supply signal?


Maybe. There has to be a return current path, of course, but
your ground connection, if long, can pick up hum.
A differential amplifier (amp + 4 resistors) configuration tolerates
grounding induced noise (like ground loops) well, and only
through a resistor does the power GND and signal GND
connect. Output signal is power-GND relative, and input
signal is signal-GND relative.

In noisy environments with long wires, simple signal/ground paired
wiring always gets in trouble, and transformers or differential
conversion is the usual solution.
 
J

Jamie

Jan 1, 1970
0
krw said:
Not directly, anyway. If the amplifier is set up as a differential
amplifier with unity gain. The output signal will be referenced to
the power supply grounds. In this configuration, the inputs ('+'
input, actually - the '-' input is along for the ride) must remain
within the common mode operating range of the Op-Amp though.

___ ___
+------|___|---+----|___|-+
| R | R |
| | |
/-\ | |\| |
( )2V +----+-\ |
\+/ Vin ___ | >--+------- +2V
+-----+|___|---+----| / out
R | |/|
|
.-.
| |R
| |
'-'
|
GND

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)






As usual for Jamie, wrong. The resistors will be the "isolation"
devices (not to be confused with safety isolation).
That is insane,,, glad you're not in my work group.

really, kind of cracks me up.


http://webpages.charter.net/jamie_5"
 
K

krw

Jan 1, 1970
0
OK, so you not only know everything,
Enough...

but you also know me?

to know that you're not only an idiot, but a jerk.
That my friend is a big error on your part.

Hardly. You advertise quite successfully.
Btw, aren't you the one that is being called
"Always wrong" ?

Wrong, again. You're just about as stupid as he, though. I'm the one
who gave him the (well deserved) "DimBulb" moniker, Junior.
Maybe I have you mixed up with another here but it seems to
fit at the moment.

Who haven't you mixed it up with? You let everyone know how stupid
you are.
And also, the original poster never commented on using differential
input for balanced pairs. So, go have your fun else where, you're
barking up the wrong tree.

He never indicated that he couldn't, either. Your *flat* assertion
that the grounds had to be the same is wrong. Perhaps you should take
DimBulb's "AlwaysWrong" name.

I'm barking up the wrong tree? I pin your ears to the wall, an *I* am
barking up the wrong tree? You are full of shit, but you've been told
that before.
 
J

Jamie

Jan 1, 1970
0
krw said:
What would be insane is *being* in your "work" group.




No, you've been there a long time.
OK, so you not only know everything, but you also know me?

That my friend is a big error on your part.

Btw, aren't you the one that is being called
"Always wrong" ?

Maybe I have you mixed up with another here but it seems to
fit at the moment.
And also, the original poster never commented on using differential
input for balanced pairs. So, go have your fun else where, you're
barking up the wrong tree.


http://webpages.charter.net/jamie_5"
 
E

Eeyore

Jan 1, 1970
0
panfilero said:
Hello,

If I have an OpAmp (a 741 for example) and I want to use it as a
buffer, and will be sending it 2Vdc, and am powering it with a dual
power supply +/-10V.... do I have to tie the grounds of my input
signal to the grounds of my power supply signal? the 2V ground and
the +/-10V ground?

You either need to do that or configure the op-amp as a differential
amplier ( in which case ensure the ground voltage of the source and the
signal remains within the common-mode voltage range of the diff
arrrangement ).

Graham
 
E

Eeyore

Jan 1, 1970
0
Jamie said:
That is insane,,, glad you're not in my work group.

You're the one who's insane. You're almost as bad as AlwaysWrong.

Graham
 

neon

Oct 21, 2006
1,325
Joined
Oct 21, 2006
Messages
1,325
A gnd is a reference point. The 741 to operate correctly both inputs must be satisfied. tie to ground yes but where becames the question obviously at the source of the signal not at the power gnd if large current flow then the IR drop can become a signal. Not only that but tie it through a ressistor what size? it should be the same total resistor that the other input sees.
 
J

Jamie

Jan 1, 1970
0
krw said:
to know that you're not only an idiot, but a jerk.




Hardly. You advertise quite successfully.




Wrong, again. You're just about as stupid as he, though. I'm the one
who gave him the (well deserved) "DimBulb" moniker, Junior.




Who haven't you mixed it up with? You let everyone know how stupid
you are.




He never indicated that he couldn't, either. Your *flat* assertion
that the grounds had to be the same is wrong. Perhaps you should take
DimBulb's "AlwaysWrong" name.

I'm barking up the wrong tree? I pin your ears to the wall, an *I* am
barking up the wrong tree? You are full of shit, but you've been told
that before.
Typical Ass whip.

Figures.



http://webpages.charter.net/jamie_5"
 
K

krw

Jan 1, 1970
0
Yes, he is my mentor. Glad you noticed!

Perhaps he's your mentor (it would figure), but there isn't any
possibility of you learning anything. You're batting zero so far and
the prognosis isn't good.
 
J

Jamie

Jan 1, 1970
0
krw said:
Perhaps he's your mentor (it would figure), but there isn't any
possibility of you learning anything. You're batting zero so far and
the prognosis isn't good.

If that is your prognoses, I'm not to worried about it. I really don't
give much credence to your commentary. You don't hold a candle to what
I'm accustom to on a daily routine.


http://webpages.charter.net/jamie_5"
 
K

krw

Jan 1, 1970
0
If that is your prognoses, I'm not to worried about it. I really don't
give much credence to your commentary. You don't hold a candle to what
I'm accustom to on a daily routine.

I understand. You're used to much worse from those who really know
you. You really are stupid.
 
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