OpAmp Gain trouble
Electronics Forum Index Electronics
Circuits, theory, electrons and discussions.
 
 FAQFAQ   MemberlistMemberlist     RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
 
Google
 
Web ElectronicsHelp.net
OpAmp Gain trouble

 
Post new topic   Reply to topic    Electronics Forum Index -> Basics
Author Message
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

Back to top
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.
Back to top
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

Back to top
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
Back to top
 
Post new topic   Reply to topic    Electronics Forum Index -> Basics All times are GMT
Page 1 of 1

 
 You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum



Home & Living New Topics
Powered by phpBB