What kind of OP-AMP circuit is this?

[drkidd22]

Hello,

I'm trying to figure out what kind of op-amp circuit this is. the input voltage to the op amp is 24VDC. I know it's a non inverting amplifier, but I'm a little confused of how to calculate the gain and output for a given input voltage. I've never seen one like this. Any help will be appreciated.

 

[ronsimpson]

In your gain calculations, short out R45 1k. It will help your head.
The 1k on the (+) input also does not effect the gain.
The output resistor, 15K, has no effect as long as there is no load.

 

[drkidd22]

Thanks, makes sense shorting the 1k.
What is the purpose of the 1k resistor? I tried looking online but can't find a reference.

 

[ronsimpson]

Several reasons:

The 1k on the + input could be there to limit the input current. If the input is more than the supply voltage there will be input current.

To reduce "input offset voltage"; we want the impedance on the + and - inputs to be the same. The two 1k resistors do not exactly do that function, that might be what the other wanted to do.

 

[fernando_g]

Perhaps they had a surplus of 1k resistors.......

Now seriously, it is most likely the first reason that Ron provided: namely to protect the opamp's inputs.

 

[audioguru]

Normally, the circuit does not use and does not need the 1k resistors at the inputs of the opamp.

 

[Winterstone]

An input voltage of 24V DC and a gain of approx. G=36 ? Looks not to good for my opinion.

 

[dr pepper]

Looking 'out' from the inputs of the opamp you see approx 1k resistnace from either input, reducing the 'offset', this offset is a dc voltage that appears on the o/p pin.
If you were making a circuit that accurately amplified a dc signal from a sensor you would go to these lengths, for ac and general purpose stuff this wouldnt be required.

 

[audioguru]

Looking 'out' from the inputs of the opamp you see approx 1k resistnace from either input, reducing the 'offset', this offset is a dc voltage that appears on the o/p pin.
If you were making a circuit that accurately amplified a dc signal from a sensor you would go to these lengths, for ac and general purpose stuff this wouldnt be required.

No.
The input bias current of the OPA2234 opamp shown is so low that the 1k resistors on the inputs do almost nothing.

 

[dr pepper]

You might be right mr guru, No. isnt exactly polite though is it.

 

[audioguru]

You might be right mr guru, No. isnt exactly polite though is it.

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