Differential Amplifier Does Not Work As Anticipated

For an application like that you need an op amp with wider common mode area and output swing that includes both rails. This is not the case for 741 and as such is more suited for dual supply. Now if positive output gets high enough for your needs as you say (and I doubt, if your + power supply is under about 12-13V), you can make a shortcut, just feed 741 with about -5 volts relative to ground on minus rail (Vee). This way, you will need just one extra power supply. S.M.

Your first line statement shows some misunderstanding of op amp basics, or it's just a brain fart, that I would also understand, cause I do it all the time. The op amp amplifies the voltage difference between + and - input by the specified amplification factor, (that is adjustable using negative feedback), period. 21.67 volts appear nowhere in the circuit. Anyway you don't care about individual input voltages, until you get out of input CMR area, and about output voltages until you go near the rails. An ideal op amp would work on OP original design just fine, hence the simulation "results". It's the real world limitations like swing and CMR that give the problem. S.M.

That's an odd part you have there for C2. Is that two capacitors with one common lead, a chassis feed through connector for the differential input voltage or what?

That is an X to Y cap or sometimes called an X and Y cap.

Essentially, it is two matched capacitors in a single package joined together at one end with that joined lead to ground. The other two ends go to pins 2 and 3.

They are used for input RFI suppression.

As SM has said, op amps won't drive all the way to the rails (especially bipolar like 741). CMOS opamps do better but still won't be linear all the way to the rails.

Maybe what you need is an instrumentation amplifier (2 inputs, 2 outputs). I think you can adjust the resistors to give you the offset and gain you need...

Just for clarification, "and it output from 2.25V to 2.75V", instead, should be ""and it output from 1.75V to 3.25V".

Looking at the low resolution images CR4 allows here I cannot say for certain what your function your circuit is supposed to perform but it is not a differential amplifier circuit. Then again your desired function description doesn't sound like a differential gain circuit is desired. There is no common mode voltage or signal mentioned applied to two terminals with amplification of the difference between these two terminals. It sounds more like you desire a gain with offset capability. Your circuit kind of looks like a gain with offset but without knowing the chip used and supply voltages available I cannot help much here.

Could you simply feed the op amp output into an open collector buffer and supply that and your load with whatever voltage you want, even from a separate power supply if that is warranted?

You will need a few minor changes to the circuitry, changing the value of the resistor across the input/output of the Lm741 (can't read the R number on your picture) would alter the gain of the circuit to whatever you require up to about 10X.

Instead go for inverting amplifier and sum the reference 1.75 volt created thr resistance divider across 6.2 v or 9 v Zener reg and the signal input thr suitable series resistances 10 to 100k value at 741 inverting input. Ground the non inverting input thr resistance of same value used for summation. Calculate resistance value for 6 times amplification and use a potentiometer in series to set the output to 10 volt for 3.4 v input. Parallel this resistance and pot combination by 0.1 mfd disc capacitor. Hope this solution solves all your problems. Refer to 741 or 301 application notes on line.

Use an ICL7660 for the negative supply, and I've had excellent linearity results with an ICL7650 chopper stabilized op amp when sensing an arc voltage that ranges between 6-16v to a 10v input (.62gain) 100meg isolation, where the open circuit power supply voltage is as high as 80v, with a 30kv high frequency arc transfer pulse. The 7650 has fast recovery from swamping. For linearity the 2 pairs of matched resistors that set the gain should be as closely matched as possible, I usually hand sort them using a wheatstone bridge.

Can U give a better resolution picture of the circuit?

I would like to do a circuit analysis for the exercise.

Be sure to include the complete circuit including the power supply to the 741.

(By the way, with a 741, depending on output load, you can only get within about 2 or 3 volts of the power supply rails.) If I see your circuit correctly, you have the voltage supply of the 741 on the voltage divider from the power supply for "10V". since the 741 can handle easily a +-12 volt supply, put the power directly across your regulated supply and with a capacitor in parallel very near the 741 to filter high frequency (10 to 100nF should be OK). You really should have a +- supply for the OA.

I would suggest using a scope to look at your signals, you may have a high frequency oscillation that trumps everything.

ref:

http://www.datasheetcatalog.com/datasheets_pdf/L/M/7/4/LM741.shtml

look at sh.3 "Output Voltage Swing"