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LM338: LM338

Patrick Nkwari
Prodigy 130 points
Part Number: LM338

Hi All,

I build the regulator as the picture. When I applied 24 V. The vout is 24V as well.

Could anyone tell me what could have gone wrong as I am using the reference schematic?

  • 0
    TI__Guru 55940 points
    Hi Patrick,

    For Vout to be at the same voltage as Vin it implies that there is either an unintentional leakage path from either Vin to Vout or from ADJ to GND. Are you able to verify the resistance of R12 and that there are no shorts between ADJ and GND? Also look for residual flux that has not been cleaned from the assembled board as flux can cause unintentional leakage paths.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Prodigy 130 points

    Ryan Eslinger said:
    Hi Patrick,

    For Vout to be at the same voltage as Vin it implies that there is either an unintentional leakage path from either Vin to Vout or from ADJ to GND. Are you able to verify the resistance of R12 and that there are no shorts between ADJ and GND? Also look for residual flux that has not been cleaned from the assembled board as flux can cause unintentional leakage paths.

    Very Respectfully,
    Ryan

    Hi Ryan,

    Thank you very much. They guy who populated my board put R12 =0.12 Ω instead of 120 Ω. 

    That resistor was almost shorting circuit the ADJ pin to ground. I change the resistor to 120 Ω.

    The circuit is work as expected. 

    Regards

    Patrick