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TL084: TL084

kirk s
Prodigy 10 points

Part Number: TL084
Other Parts Discussed in Thread: DIYAMP-EVM, TLV171

I am using the TL084 in a follower configuration.  I am using a +/-12vdc supply that measures about +12.13vdc and -12.14vdc.


When I input a positive dc voltage the output follows the input.  When the I decrease the input and it  reaches about -10.5 volts, it stops following

the input.  When the input voltage reaches about -11.3vdc, the output jumps to a +10.5vdc or so.

The TL084 is an older part.  I put in a new one.  I also built the circuit on a breadboard and got the same results.

Can someone let me know if this is operating correctly and if you don't know build one and test it?

Thanks

  • 0
    TI__Mastermind 25865 points
    Hello kirk s,

    Given a +/-12V supply, the TL084 has the following linear operating region according to the recommended operating conditions table:

    Input Common-mode (min/max):
    -8V<Vcm<8V

    Output Swing (10kohm load, minimum):
    -9V<Vom<9V

    While the typical (~68% of devices) common-mode range is -12V<Vcm<15V, it's possible that you received a device(s) that is one of the remaining ~32%. You will notice in the data sheet that the minimum value is +/-11V, which is the tested value. That is why you can get down to -11.3V before observing the odd behavior.

    What you're observing is called phase reversal. It happens when the input signal exceeds the linear operating region of the device. Newer amplifiers have circuitry that prevent this behavior. Therefore I suggest that you evaluate a newer device. I suggest evaluating the TLV171. You may also be interested in the DIYAMP-EVM. Finally, we have an excellent series of videos called TI Precision Labs (www.ti.com/precisionlabs). You may find the videos on Input and Output Limitations particularly useful.