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317 reg

Discussion in 'General Electronics Discussion' started by conntaxman, Dec 7, 2011.

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  1. conntaxman

    conntaxman

    89
    0
    Jun 17, 2011
    Why am i getting about 3 volts on the out put when I should be getting about 1.5 volts.
    For R1 i have a 240ohm and for R2 i have a 48 ohm. I didn't not put a load on it. Just tested it with my ohm meter. oh imput was 10vdc
    tks
    John
     
  2. jackorocko

    jackorocko

    1,284
    1
    Apr 4, 2010
    Isn't the minimum voltage around 2.75V or something like that for a 317 VR
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,419
    2,790
    Jan 21, 2010
    Min voltage is about 1.25 volts (Vref for the regulator)

    Presuming R2 isbetween the output and the adjust pin and R1 is between the adjust pin and ground, I'd also be expecting about 1.5V.

    Do you have a capacitor on the input and output? If it's oscillating you may be getting very odd readings
     
  4. conntaxman

    conntaxman

    89
    0
    Jun 17, 2011
    .
    Yes i have a 0.1uf on both in and output. what im trying to do is feed a small transistor radio that has a 1 1/2 volt battery.
    tks
    John
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,419
    2,790
    Jan 21, 2010
    Does the output voltage change when you apply a load? Try a resistor between 100 and 470 ohms.

    Also double-check you have the pins the right way around.

    Can you show us a photo of your circuit?
     
  6. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Yes the pin notation can throw you first time, in a schematic its 123, but in reality the pins out is different, i cant remember of hand, but it can throw you first time. You have input ajust and output, but not in that order, its is on paper but different in use, IE pin notation.
     
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