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lm1084-adj issues

David Baines
Prodigy 20 points

I implemented a basic adj circuit, r1=120ohm(output to gnd pin), r2 = 5k pot (ground pin to GND).

It was working on first tests, on a 12V source I could move it anywhere from 1.25V to ~11.5V with the pot.

Now its stuck at max, always Vin - 0.3V. I see no burning or overheating, the regulator gets I'd call very warm after about 2 min with no direct load.

Is it the regulator or something else?  (I've confirmed that the pot works fine)

 

Thanks.

 

 

  • 0
    TI__Mastermind 22610 points

    I presume that you mean ADJ pin.

    Knowing the voltage at the ADJ pin, or across the 120 ohms, might be helpful.

    Either the device is damaged, or the pot connection to the ADJ pin is open, or the pot connection to GND is open, or the 120 ohms connection from Vout to the ADJ pin is open 

    If the part gets warm then there is current going somewhere.

  • 0 in reply to Donald Jones
    Prodigy 20 points

    The 120 measured 98 ohms, the pot was good.

    Measuring the voltage across the 120 resistor was Vin - 0.3v, which is obviously the issue.

    Clearly not the 1.25v it should be, I'll change it out and see if it fixes the issue.