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TL074: Vin condition and output confirm

Wenhsiang Lin
Intellectual 520 points
Part Number: TL074
Other Parts Discussed in Thread: LM258

Hi Team:

There are two question feedback from customer , please help ti , thanks a lot.

1.If only provide +12V and -12V disable (not provide voltage) , TL074_pin7 output will be 3.3V ? (fig as below)

2. If only provide +12V and -12V disable (not provide voltage) , RC726、RC727 open then Pin3 have 1.5V , TL074 like a  positive saturation of comparators and output Pin 1 will be +12V ? 

Regards / Mark

  • 0
    TI__Intellectual 775 points

    Hi Wenhsiang,

    If the negative supply (-12V) is just floating when it is disabled, it will not work. Op amp supply current needs to find its path to negative supply or GND.

    I know some power supply like buck-boost or negative LDO has an internal FET that would short the output of the power supply to the gnd when it is disabled. If the negative supply is pulled to the ground then it is equivalent to an op amp working in single supply condition (positive rail and gnd). In this condition, it will work.  So you have to find out how the negative power supply works when it is disabled. 

    I hope I answered your question.

    Regards,

    Sanjeev

  • 0 in reply to Sanjeev Manandhar
    Intellectual 520 points

    Hi Sanjeev Manandha:

    If it's for voltage follower application Vin=3.3V and Vout=3.3V , RD setup +Vcc=12V and -Vcc connect to GND , is OK ?

    or change it like to LM258 only +Vcc non -Vcc(connect to GND)  , which one is more better ? please help to comment , thanks a lot.

    Regards / Mark

  • 0 in reply to Wenhsiang Lin
    TI__Intellectual 775 points

    Hi Mark,

    For the voltage follower application, if you have Vin=3.3 V and want Vout 3.3V positive supply(+VCC) connected to 12 V and negative supply (-VCC) connected to GND is good. It will work.

    I did not understand what you asked in the second sentence "change it like to LM258 only +Vcc non -Vcc(connect to GND)", what does this mean? 

    Regards,

    Sanjeev

  • 0 in reply to Sanjeev Manandhar
    Intellectual 520 points

    Hi Sanjeev Manandha:

    Sorry let you confused , I mean use the TL074 with +- Vcc which connect to GND more better or select only +Vcc tpye more better as below , thanks.

    Regards / Mark

  • 0 in reply to Wenhsiang Lin
    TI__Intellectual 775 points

    Hi Mark,

    Connecting -VCC to GND is better than floating it when there is not a negative supply.

    Regards,

    Sanjeev