• State Answer Suggested
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 49 subscribers
  • Views 839 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

why OPA129 cannot be used as a voltage follower, what is wrong

Peng Sun
Prodigy 90 points

the circuit is attached.

When I measure the potential, it is 13.5V. I thought the opa129 is damaged, so I used two brand new opa129, it still gives me the same thing.why can that happen?

  • 0
    Expert 2580 points

    Hi,

    you connected the positive Input with the Output, if your Image is correct.

    Each voltage rise at the positive Input (like Offset voltage) causes a rise of the Output voltage. As you connected out to the positive Input the positive Input raises too, which causes a raise of the Output and so on ...

    You end up with an Output value which reflects the max. voltage swing of the Output, here 13.5V.

    Nothing wrong with the Chips, just connect the Output to the negative Input and use the positive Input for the Input Signal and it will work fine as voltage follower.

    With best regards

    Gerhard

  • 0
    TI__Guru 60610 points

    Peng,

    In order for the output to follow the input, you must use a negative instead of positive feedback shown in your diagram - this is the reason for the output collapsing toward the rail (13.5V).   In order to correct the problem, please connect the input voltagel (10k resistor ) to pin 3 while the negative input (pin 2) must be connected to the output (pin 6).

     

  • 0 in reply to Marek Lis
    Prodigy 90 points
    Hi,
    Thank you very much for your reply.
    I am a new hand, low current amplification is my new hobbies.
    again, thank you for your help
    Peng