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LM1084: Output Voltage Drop when Load Applied

Hong Tay
Expert 2465 points
Part Number: LM1084

Hi Sir/Madam,

Please help to advise on the issue. There is unexpected voltage drop when load applied. The input voltage is 12V and the output voltage is 7V, connected to load circuit through a long wire.

The expected output voltage, 7V is obtained when it is not connected to the load circuit. Unexpected voltage drop to 2.4V when the load circuit connected. Please refer to the circuit for the LM1084 and load circuit as attachment.

Hope to hear from you soon. Thank you very much.

  • 0
    Intellectual 515 points
    Might not be directly related but your upper resistor (R45 / 330R) value is too large.
    The LM1084 has a minimum load current requirement of 10mA.
    I would suggest R45 of 121 ohms, which follows the datasheet suggestions.
    Or a fixed divider using 113 ohms for the upper resistor and 523 ohms for the lower resistor. These are 1% (E96) standard values.
  • 0 in reply to Daddio
    TI__Guru 55940 points
    Hi Hong,

    In addition to Daddio's suggestions, could you attach a scope shot of Vin, Vout, and Iout for your application? This will help us better assist in debugging your application.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Expert 2465 points
    Hi Ryan,

    Thanks for your kind help. The issue was solved after implement the suggestion from Daddio.

    Thanks.
  • 0 in reply to Daddio
    Expert 2465 points
    Hi Daddio,

    Thank you very much. The issue is resolved.