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Summing non inverting op amp.
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daveatfernie
electronics forum beginner


Joined: 02 May 2006
Posts: 5

PostPosted: Tue Jun 27, 2006 8:42 am    Post subject: Summing non inverting op amp. Reply with quote

Hi,
I've a voltage change 3-4 Volts which I need to change into a 0 to 4
Volt signal.
I have used an inverting op-amp with a virtual ground to give a
cracking result but unfortunately the voltage is going the wrong way
(decreasing instead of increasing.

I have changed to circuit over to be a non inverting amplifier but I'm
worried about the virtual ground. I've been told that summing in a non
inverting op amp can be difficult.
I took the series resistors out of the circuit from my virtual ground
(created from a pot) and from the voltage that I'm amplifying. I have
a 560K feedback and 220K to ground giving me a gain of around 3.5.

Will I have problems with the virtual ground being amplified to or any
other problems?

Many thanks in advance.

David
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daveatfernie
electronics forum beginner


Joined: 02 May 2006
Posts: 5

PostPosted: Tue Jun 27, 2006 9:05 am    Post subject: Re: Summing non inverting op amp. Reply with quote

If I was to conect my ground resistor to my virtual ground would this
be a better circuit. I'm now worried that my offset voltage from the
virtual ground will also be amplified by the op amp.

Cheers again

David
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jasen
electronics forum Guru Wannabe


Joined: 18 Jun 2006
Posts: 204

PostPosted: Wed Jun 28, 2006 8:49 am    Post subject: Re: Summing non inverting op amp. Reply with quote

On 2006-06-27, daveatfernie <Daveatfernie@gmail.com> wrote:
Quote:
Hi,
I've a voltage change 3-4 Volts which I need to change into a 0 to 4
Volt signal.
I have used an inverting op-amp with a virtual ground to give a
cracking result but unfortunately the voltage is going the wrong way
(decreasing instead of increasing.

I have changed to circuit over to be a non inverting amplifier but I'm
worried about the virtual ground. I've been told that summing in a non
inverting op amp can be difficult.

do you need a virual earth or summing amp?

Quote:
I took the series resistors out of the circuit from my virtual ground
(created from a pot) and from the voltage that I'm amplifying. I have
a 560K feedback and 220K to ground giving me a gain of around 3.5.

Will I have problems with the virtual ground being amplified to or any
other problems?

huh?

Your description of the problem seems to call for something like this.

|\
in------------|+`\
| >---+------>
.--|-,/ |
| |/ |
| |
4V--[110K]-+---[330K]-+


Bye.
Jasen
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