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TL072

zahra meghjani
Prodigy 20 points
Other Parts Discussed in Thread: TL072

I have the dual op amp TL072. Firstly, the spec sheet says the maximum output voltage swing would be around +- 12 VDC at a supply voltage of +-15vdc. But we noticed that the output gets saturated at 5.7 V. Its not going anywhere near 12 V.

Secondly, amplification factor of 10, 100 gave me results but as soon as I try 1000 amplification i am getting weird output. i was giving inputs around 4mv with rf=1ohm mega and ri=1k ohm

Anyone experienced a similar problem or have any clue why this might be happening? please reply.  

  • 0
    TI__Guru**** 168876 points
    Zahra,

    First thing to check is input voltage (at TL072); is it greater than [VCC-] +4 V to be in the proper input common mode range?

    With a DC/AC gain of 1000, the output voltage will be (VIN + VIO) * 1000. Both the input and the VIO (offset error) with get the gain.
    Is your amplifier inverting or non-inverting?
  • 0 in reply to Ron Michallick
    Prodigy 20 points

    it is a non-inverting type.

    the input is 4-5mv as of now and the supply is +-15vdc.

    Another odd thing i noticed was when i was trying to get amplification factor of 1000 using rf 1Mohm and ri 1Kohm i was not getting the correct output. but when i change them to 100Kohm and 100 ohm i got 1000 times amplification.

    how is it related to selection of resistors?

  • 0 in reply to zahra meghjani
    TI__Guru**** 168876 points
    Zahra,

    Perhaps the higher resistances caused oscillation because of the small capacitance on the inverting input (board and op-amp). A small capacitor like 10pF across the feedback resistor should fix that.