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# Help needed for opamp offsetting!

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#### picstudent

##### New Member
Hello

My input signal is 3.3V to 5 volts.

I need to amplify and offset this to 0 to 5 volts.

3.3V to 5V should be converted to 0 to 5V for ADC.

Is it possible to implement using Opamp(s) with +12V supply. No negative rail.

Thanks

Last edited:
Hello

My input signal is 3.3V to 5 volts.

I need to amplify and offset this to 0 to 5 volts.

3.3V to 5V should be converted to 0 to 5V for ADC.

Is it possible to implement using Opamp(s) with +12V supply. No negative rail.

Thanks

Hi,
Its possible to get within about 10mV close to 0V, using a TLC358 or CA3140 OPA.

EDIT:
Are you asking for circuit diagram.?

Last edited:
Are you asking for circuit diagram.?

It will be helpfull defenitly, The values I can correct by simulation and trial, But needs an idea How to do this offsetting. The opamp offset voltages I can manage.
Some online resistor calculators seems not working in this values.

Thanks

to get such controle voltage, use a potentiometer. connect first leg to pin 5, center to gnd and last to pin 1 of a lm741 ic. a 5 to 10k potentiometer can do it. I don't know if you have done ths before, then you have done that before you have to try other ics or go googling

It will be helpfull defenitly, The values I can correct by simulation and trial, But needs an idea How to do this offsetting. The opamp offset voltages I can manage.
Some online resistor calculators seems not working in this values.

Thanks

hi,
Have a look at this option, with a CA3140 or TC358 it will get within 10mV or so of 0V , using a single +12V supply.

Note: using a 12v supply means that the output could go higher than +5V while setting up.
To protect the ADC input connect the OPA output to the ADC input via 470R resistor, this will not affect the performance of the ADC.

#### Attachments

• OPAoffset1.gif
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Last edited:
Thanks a lot for the circuit.
btw Why you use this 4.7V Reference? I have +5V on board. Any consequence if I change by changing resistors suitably. I will try in simulator.

Thanks a lot

Roy Thomas

hello
Thanks for the circuit.
I am using Proteus for simulation. There CA3140 is not showing correct values, but when I replaced op amp with LM358 it gives almost acceptable values in simulation.

Thanks again. I am looking for a Anti aliasing filter circuit also.( Single supply). I will start another thread.

Thanks

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