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LM358: Output voltage 0.03V

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Replies: 8

Views: 78

Part Number: LM358

Even at zero input voltage the LM358 gives 0.03V output.

Problem is that this signal corresponds to frequency. It shows 18RPM with zero input voltage. Can I reduce the output offset to 0.1mv ??

  • Hi Saurabh,

    the output voltage of OPAmp cannot fully reach the negative supply rail (0V):

    One remedy is to use a small negative supply voltage instead of 0V. The LM7705 could be used, e.g..

    Kai

  • Hello Saurabh,

    Output voltage could be the result of offset voltage or it may a result of load current. In some cases, it is the result of different ground potentials. 

    What is the (non inverting) gain of the the circuit and the load current magnitude and direction? Remember, that the feedback network is part of the output load.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Hello Saurabh, 

    Like Kai mentioned, this is due to output swing limitation. As you can see from the datasheet for a 5V supply, the negative rail can swing as close as 5mV (typical value) to the negative rail. One solution is to use a dual-supply, if you need the output to be 0V.

    I will go ahead and close this thread for now. Please let us know if you've any further questions. 

    Regards,

    Bala Ravi

  • In reply to Bala Ravi:

    Thanks everybody to provide some useful insight!!

    It is clear that providing a negative voltage could solve the issue. 

    But in this case I am limited to +15V and GND. I need options within this supply range.

    As of now I have come a conclusion of replacing the IC namely LM358 (2mV offset) by other low offset voltage, precision amplifier OP-AMP IC.

    Any study material or video link to showcase, the reduction in offset voltage of OP-AMPS ,from any of the esteemed members is highly appreciated.

    Thanks.

  • In reply to saurabh kshirsagar:

    Hi Saurabh,

    it's not so much a question of input offset voltage but of output voltage swing. So, choosing an ultra low offset voltage OPAmp will hardly solve the issue.

    Can you show a schematic of your circuit?

    Kai 

  • In reply to kai klaas69:

    Hi Kai ,

    Following is the schematic with values and a DAC at its input.

  • In reply to saurabh kshirsagar:

    Saurabh,

    Can you measure the voltage at op amp pins 1,2,3?  Where does "Analog_OUT2" go?  Does any current flow here?

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to saurabh kshirsagar:

    Hi Saurabh,

    I would again recommend the LM7705. It generates a negative supply voltage of -0.232V, simply out of the positive +5V supply. Have a look into the datasheet of this very nice "trouble shooter"! Also, choose a better OPAmp than the LM358. Take an OPAmp with input-output-rail-to-rail ability which can also work with a +5V (and -0.232V) supply voltage. TI has lots of them.

    Or you might also want to think about the use of one of TI's charge pumps. These produce a negative supply voltage entirely out of the positive supply voltage:

    Kai