LM321: LM321 doesn´t work like buffer

Javier,

LM321 can be a buffer.
With a load to ground (or no load), the buffer will follow input from 0V to VCC -2V

Can you provide examples of vin and vout?
Knowing output load and VCC would also be helpful.

Hello Ron.

Vin have a range of 0v to 5v, Vin is a analog signal.
Vout is connected to input analog of microcontroller.

Power supply of LM321 is 12v.

Regards!!!

Javier,

That setup is good. Vout should be very close to VIN.
Is this a new or old design? What is the failure rate?
Because output is too low, be sure to measure VCC at the LM321 VCC pin.

Hello Ron.

This is a new desing.

I have used LM321 in other desing as comparator and this desing run OK.

The failure range is high, because I have 2.5v in Vin and register 0.8v in Vout.

In this post, I am attaching schematic.

Regards.

Javier,

The unity gain amplifier is the most simple amplifier setup. However valid input and output ranges give good results. This is not the problem here, so I suggest using an oscilloscope to check op amp input and output pins. Input should be DC with too much ripple if input is 330 Hz PWM. Output should follow input.

I built a LM321 unity gain amp setup and tested with DC sweep from -1V to 15V (-1V is not allowed, but I did it anyway).

Hi Ron.

I think that the problem is brought about a ripple in the analogic signal, because I used this circuit with DC input and the Vout in LM321 is Vin+0.11v.

Is my teory correct?

Regards.

Javier,

Yes that is likely part of the issue. You can reduce input ripple with a larger value for C8