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LM331

eli
Guru 13485 points
Other Parts Discussed in Thread: LM331

Hi

Can you help with below/attached:

The attached  design produce isolation for a DC input supply 

The main idea based on  Voltage to frequencies -> Optocoupler (For Isolation) -> Frequencies to voltage 

Customer  would like to get Frequencies response from 0.5vdc-10vdc but in fact he getting frequencies only above 2.5VDC 

Can you. review the attached design  and send me your comments/feedback?

5483.TRILOGICAL Train_Project.pdf

  • 0
    Guru 13485 points

    Hi

    Any feedback?

    B.regards

    Eli 

  • 0 in reply to eli
    TI__Genius 16890 points

    HI Eli,

    The circuit has 3 parts: V to F, Optocoupler, F to V.  In what section does the problem occur?

    Some tips for making these type of circuits work are:

    Rs:  Make this value between 12k to 16k.  Making this resistor too small can take too much current from the internal circuit.  14k may be a good value to start with.

    Ct should be a NP0 type. 

    CL (the 1uF) needs to be a mylar (best) or ceramic (ok) type of capacitor.  This cannot be an electrolytic capacitor.

    Mike

  • 0 in reply to Michael Stout
    Guru 13485 points

    Attached design for train Project 

    The concept of the design based on LM331 

     The problem concern with the fact that customer  can’t achieve linearity from input to output 

    V_IN_1 – Input voltage to V/F (LM331)

    PRESS_SNS_OUT– Output Voltage   from the secondary LMM31 (F/V) 

    Any reason why?

    6747.Press Sns.pdf

  • 0 in reply to eli
    Guru 13485 points

    Any feedback?

  • 0 in reply to eli
    TI__Genius 16890 points

    HI Eli,

    As I mentioned above, the circuit has 3 parts: V to F, Optocoupler, F to V.  In what section does the problem occur?   Until they determine that there is no way to troubleshoot the problem.

    This means they need to measure the input and output of U2 and determine if the problem is there.  The input will need to be swept over the entire range of interest.  If that is ok then measure the input and output of the optocoupler to see if the problem is there.  If that is ok, then measure the input and output of U6 and see if the problem is there. 

    Did they check that they are following the tips I had listed above?  I have listed them again below:

    Rs:  Make this value between 12k to 16k.  Making this resistor too small can take too much current from the internal circuit.  14k may be a good value to start with.

    Ct should be a NP0 type. 

    CL (the 1uF) needs to be a mylar (best) or ceramic (ok) type of capacitor.  This cannot be an electrolytic capacitor.

    Mike

  • 0 in reply to Michael Stout
    Guru 13485 points

    Hi Mike

    According to the customer,The circuits are working! 

    The problem is  the fact that at 3 different circuits customer getting  different results although the components are the same! And the input voltage is the same 

    Does it make any sense that 3 different circuits will bring different output voltage?  

  • 0 in reply to eli
    TI__Genius 16890 points

    Hi Eli,

    It could be caused by the tolerances of the external components.  Tolerances of CL and RL and Ct and Rt could cause a variation between boards.

    You can try swapping parts from a board that is performing correctly into a board that is not.  Does the problem follow the board or the parts?

    Mike