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LM258A: LM258A/LM2904 Pls help to suggestion How to improved current sensing circuit operation range -20C to 80C ?

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Replies: 3

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Part Number: LM258A

Dear All

Pls help to suggestion How to improved current sensing circuit operation range -20C to 80C ?

Test result is below .

@ 25C   set current is 3.958A  the output opamp is 2.493V   the result is PASS

@ 55C   set current is 3.625A the output opamp is 2.493V  the result is FAIL because the power supply is not operation at max load(3.791A )

@ -20C   set current 4.166A the output opamp is 2.493V  the result is FAIL  because the power supply is not protection by current limit ( 3.958A current limit ) 

Remark :

1.The maximum output current of PSU is 3.791A  

2.Current limit is 3.958A  

Thank you so much&Bestregard

Prarinya

  • Hello Prarinya,

    Using your data I see that the change in current from -20C to 55C was 541mA. This is a 5.41mV difference in sense resistor voltage. That is a big change. The 4.7uF direct capacitance on the output far too much. In general, there should be no direct capacitance on the output at all. Does removing this capacitor help?  The feedback R and C has a crossover at 1Hz. Do you only want only the average current and can tolerate lag?  Last but just as important, make sure that the 1.21k resistor and the non inverting resistor have a kelvin connection to the sense resistor.

     

    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:

    Dear Ronald

    Thank you so much for your help .Pls help again 

    How to adjust R-C network of circuit to  meet current limit (3.958A ) in all temperature rang of device ?

    Thank you so much&Bestregard

    Prarinya

  • In reply to prarinya Maneechompoo:

     Prarinya,

    Start by removing the 4.7uF capacitor. This may be all that is needed.

    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).

     

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