Op Amp Clipping

[cswanson]

I am confused as to why I am receiving a clipped signal at Vtop 2.76 when I am supplying a voltage of +- 5v to the op amp CA3140E.

The signal is a 1Khz sine wave Vpp 800 mV. The circuit inputs the signal to a CA3140E (http://www.jameco.com/Jameco/Products/ProdDS/12204.pdf) with an inverting configuration. Rf is 47K Ohm and Re is 10K Ohm for an A=4.7*signal.  This output is sent to another CA3140E with Rf=Re=10K Ohm. However, I am applying a voltage from a V divider of R1=6.8K Ohm and R2=1K Ohm. I have the intention to raise the signal to vary above 0V for input to an ADC. Ideally the sine wave will vary between 0 and 5V.

The purpose of this is to 1) Learn about Op Amps and 2) create a circuit to record pH values for a pH sensor.

I am using this url as a guide, but I am having problems getting it to function which could be a limitation of my understanding or any other reason: https://www.sparkyswidgets.com/portfolio-item/ph-probe-interface/.

What I am confused about is the output signal from the second CA3140E is clipping at 2.76V and I believe the op amp should have enough headroom since it has a supply of +- 5V.

What am I overlooking?

ps.: I am providing the +-5V supply to the op amps using a 7660C charge pump configured as a supplier of negative voltage.

http://www.jameco.com/Jameco/Products/ProdDS/51174.pdf

[Simon]

Check that the output can go that close to the supply rails. Some opamps won't go closer than 3V to the power rails

[SeanB]

And the 3140 is one of them.It will go down to the negative rail with no load, but will only go to 3v below the positive rail. With a 5v supply that means the output will only swing from 0v to 2V max.

[cswanson]

Thanks!

Can you recommend a different op amp that may be able to deliver what I am looking for?

[Simon]

I am told LM358 as i too had the same problem last weekend.

[SeanB]

Look for rail to rail input and output opamps, probably those with a max supply of 6V are likely to be usable.

[cswanson]

Fantastic! Thanks