OpAmp Gain trouble
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OpAmp Gain trouble

 
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bunny
Guest
Posted: Thu Dec 01, 2005 3:47 pm    Post subject: OpAmp Gain trouble Reply with quote
I am using the below schematic for a OpAmp TLC272CP. According to the
formula of G = (R1/R2) the gain on this circuit should only be a matter
of 11. however as you can see below it's closer to 15/16. I'm
wondering what could cause this anomoly. I have put the circuit
below(sorry for the Ascii) and what i put into the + of the opamp and
what i got as output.

Thanks



base=2.0mv
output=33.4mV


+9V +9V
| (+). |
100k pot<------|\|
| (-)| \_____.__R3____Meter__.
| .-| / | |
| | |/| | |
| | | | |
| .------R2-' |
| | | |
| R1 | |
| | | |
Gnd Gnd Gnd Gnd

R1 = 1k
R2 = 10k
R3 = 10k

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Andrew Holme
Guest
Posted: Thu Dec 01, 2005 5:07 pm    Post subject: Re: OpAmp Gain trouble Reply with quote
bunny wrote:
Quote:
I am using the below schematic for a OpAmp TLC272CP. According to the
formula of G = (R1/R2) the gain on this circuit should only be a matter
of 11. however as you can see below it's closer to 15/16. I'm
wondering what could cause this anomoly. I have put the circuit
below(sorry for the Ascii) and what i put into the + of the opamp and
what i got as output.

Thanks



base=2.0mv
output=33.4mV


+9V +9V
| (+). |
100k pot<------|\|
| (-)| \_____.__R3____Meter__.
| .-| / | |
| | |/| | |
| | | | |
| .------R2-' |
| | | |
| R1 | |
| | | |
Gnd Gnd Gnd Gnd

R1 = 1k
R2 = 10k
R3 = 10k

G = (R1+R2)/R1 = 11

According to the datasheet, that op-amp has a 1mV typical input offset
voltage.

Try a larger input voltage e.g. 20mV or 200mV.
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Pooh Bear
Guest
Posted: Thu Dec 01, 2005 5:16 pm    Post subject: Re: OpAmp Gain trouble Reply with quote
bunny wrote:

Quote:
I am using the below schematic for a OpAmp TLC272CP. According to the
formula of G = (R1/R2) the gain on this circuit should only be a matter
of 11. however as you can see below it's closer to 15/16. I'm
wondering what could cause this anomoly. I have put the circuit
below(sorry for the Ascii) and what i put into the + of the opamp and
what i got as output.

answered in s.e.d.

Such questions should be cross-posted to avoid stupid duplication and waste
of time.

Graham

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Bob Monsen
Guest
Posted: Fri Dec 02, 2005 9:25 am    Post subject: Re: OpAmp Gain trouble Reply with quote
On Thu, 01 Dec 2005 09:47:31 +0000, bunny wrote:

Quote:
I am using the below schematic for a OpAmp TLC272CP. According to the
formula of G = (R1/R2) the gain on this circuit should only be a matter
of 11. however as you can see below it's closer to 15/16. I'm
wondering what could cause this anomoly. I have put the circuit
below(sorry for the Ascii) and what i put into the + of the opamp and
what i got as output.

Thanks



base=2.0mv
output=33.4mV


+9V +9V
| (+). |
100k pot<------|\|
| (-)| \_____.__R3____Meter__.
| .-| / | |
| | |/| | |
| | | | |
| .------R2-' |
| | | |
| R1 | |
| | | |
Gnd Gnd Gnd Gnd

R1 = 1k
R2 = 10k
R3 = 10k

Get rid of R3.

Also, try making a few measurements, and plotting the output vs input for
input = .5, .4, .3, .2, .1... That might give you a clue as to what is
happening.

---
Regards,
Bob Monsen

Music is the pleasure the human soul experiences from counting without
being aware that it is counting.
- Gottfried Leibniz
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