How can I add DC offset to voltage buffer input signal?

I am using an LM741 IC as a voltage buffer.

Attached below is the circuit diagram I am using. The AC input signal to the buffer is about 3.3V peak to peak.

enter image description here

  • 2
    \$\begingroup\$ The easiest is by AC coupling the input to the desired DC level. You anyway must to do this, because your 3.3 Vpkpk input wave is below the negative supply. Using a 741 with only 5 V of total supply is almost doomed to fail anyway. So first start by understanding the common mode input voltage range of opamps. \$\endgroup\$
    – tobalt

That's not going to work with an LM741 and a 5V power supply.

  • The LM741 inputs are not rail to rail. When the input voltage is too close to 5V or 0V, then the op-amp will not behave as you expect it.
  • The LM741 output is not rail to rail. It cannot drive its output to 5V or to 0V. The best you can expect is a range between about 2V and 3V.

You'll need an op-amp that is designed for rail to rail operation (input and output) on a single 5V rail.

Once you have a proper op-amp, you can implement the DC offset as described in this earlier answer:

enter image description here

You need to look at the values for "input voltage range" and "output voltage range" in the datasheet of the op-amp.

Here they are for the LM741:

enter image description here

That's when operating on +- 15V rails. The difference betwen the rail voltage and the input range and output range is around 2 to 3 volts.

That difference changes a bit depending on current, but no much depending on the voltage rails.

When operating on 5V, the difference between the rails and the input and output voltages are pretty nearly "closed up."

If you get lucky, your 741 might have only a 2V difference between the rails and the output voltage - leaving 1V for operation between about 2 to 3 V. Same with the input.

If you are unlucky, your 741 might have 3V between the rails and the output (and input.) That leaves no usable range at all.


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