Electronics > Projects, Designs, and Technical Stuff

Provide offset voltage for non-inverting amplifier

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Zero999:

--- Quote from: oschonrock on August 01, 2020, 07:24:58 pm ---
--- Quote from: David Hess on August 01, 2020, 07:19:36 pm ---Add the offset at the bottom of the feedback divider.

--- End quote ---

+1 to that. Was going to write the same thing and this is very common when using single ended op-amps

--- End quote ---
Yes, that'll work, but it requires a negative supply and only works for gains >1.

TimFox:
Non-inverting feedback amplifiers made from op-amps must have a gain of +1 or more.  You would have to add a voltage divider in front of the amplifier to reduce the gain.
Inverting amplifiers can have negative gains with magnitude greater than or less than 1, with appropriate input and feedback resistors.

oschonrock:

--- Quote from: TimFox on August 01, 2020, 09:24:50 pm ---Non-inverting feedback amplifiers made from op-amps must have a gain of +1 or more.  You would have to add a voltage divider in front of the amplifier to reduce the gain.
Inverting amplifiers can have negative gains with magnitude greater than or less than 1, with appropriate input and feedback resistors.

--- End quote ---

Correct, but non-inverting summing amplifiers need a gain of say 2 (1+1)  for 2 balanced inputs to results in a "gain of 1 sum". See zero999's circuit and that video.

oschonrock:

--- Quote from: Zero999 on August 01, 2020, 08:12:45 pm ---
--- Quote from: oschonrock on August 01, 2020, 07:24:58 pm ---
--- Quote from: David Hess on August 01, 2020, 07:19:36 pm ---Add the offset at the bottom of the feedback divider.

--- End quote ---

+1 to that. Was going to write the same thing and this is very common when using single ended op-amps

--- End quote ---
Yes, that'll work, but it requires a negative supply and only works for gains >1.

--- End quote ---

Agree with gain of >1. But the O/P was a little vague about what gain he actually wanted, and he is using a non-inverting amp, so this is already the case no? If non-inverting meets the requirements without the offset then it still should?

Not sure the negative supply point is correct. Are you sure about that? We are not proposing to put -2V there. It should be +2V where ground is normally in a non-inverting amp. You might run out of headroom at the top in all cases, but that's entirely separate and we just don't have enough information about what the OP actually needs.

We are in danger of over analysing this. OP isn't even around any more ;-)

Zero999:
A negative power supply is required for David's suggestion, because the bottom of the feedback divider goes to the  inverting input.

--- Quote from: David Hess on August 01, 2020, 07:19:36 pm ---Add the offset at the bottom of the feedback divider.


--- End quote ---

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