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Wiring Voltage Regualtor

Discussion in 'General Electronics Discussion' started by pizoman, Feb 9, 2013.

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  1. pizoman

    pizoman

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    Mar 10, 2012
    Help Wiring Voltage Regualtor

    I found this circuit diagram for a LM1084 regulator and I've wired it up on my bread board but I'm a little confused as to where the "final regulated voltage" is suppose to go. I've placed positive and negative multimeter probes accordingly and I get zero volts from the output voltages. Can someone help me out with this?

    Here's the original schematic: http://www.electroniq.net/power-supply/lm1084-voltage-regulator-circuit.html

    Breadboard Wiring. For some parts I used different values because those were what I had on hand.
    Specs: Top R=470ohm, Bot R=1K, 1uF electrolytic cap, 0.1uF ceramic cap, 9 volt battery source

    [​IMG]
     
    Last edited: Feb 9, 2013
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Do you mean this?

    [​IMG]

    I'd start with using the larger capacitor on the input, and I would recommend using a capacitor larger than 0.1uF on the output.

    You could also start with the simplest design, remove all the resistors an connect the adj pin to ground. I expect you should see 1.25V on the output.

    It's also worth checking the input voltage. If you're using a battery it is possible that it's flat and the current drawn is loading its voltage down.
     
  3. pizoman

    pizoman

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    Mar 10, 2012
    Yes, that's the one. Battery should be fine, I checked and it was about 8.6 Volts. I will try a larger capacitor and ground the adj with no resistor.
     
  4. pizoman

    pizoman

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    Mar 10, 2012
    Removed all the resistors and grounded the adj. Placed a probe on ground and one at the output pin of the regulator and read 7 Volts. The battery warms up too.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    If the battery warms up, you have connected something wrong.

    The output should be 1.25V with the ADJ pin grounded.

    You may have the pins connected incorrectly.

    You've removed ALL the resistors, right?
     
  6. pizoman

    pizoman

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    Mar 10, 2012
    Ok, I flipped the regulator over, I thought the pins were (from left to right) adj, out, in with the label of the regulator facing me. I get 1.3 Volts now, but the regulator heats up now.

    Also, I switched out the caps to 10uF on the Vin side and 47uF on the Vout side.
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    NOTHING should heat up. Are you sure you have no load attached?
     
  8. pizoman

    pizoman

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    Mar 10, 2012
    Nothing is attached.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    OK, we need so see a picture of your layout, because *something* is incorrect.

    What is your source of 9V?
     
  10. pizoman

    pizoman

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    Mar 10, 2012
    Power source is a 9 volt duracell battery.

    [​IMG]
     
  11. davenn

    davenn Moderator

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    no, we need to see an actual pic of your assembly so we can see if you have wired something incorrectly


    Dave
     
  12. davenn

    davenn Moderator

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    looking at the datasheet for the regulator your last drawing layout is incorrect

    you have the input voltage going to the adj pin

    Dave
     
  13. davenn

    davenn Moderator

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    here's a modified layout


    [​IMG]


    NOTE on the regulator
    AD = Adjust
    OT = Output
    IN = Input


    Dave
     

    Attached Files:

  14. pizoman

    pizoman

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    Mar 10, 2012
    Davenn, I tried your wiring and the battery no longer heats up, but I measure the output voltage to be 7.7 Volts now from what Steve said should be around 1.25V.
     
  15. davenn

    davenn Moderator

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    OK I go back to my earlier comment again

    SHOW us an actual photo of your setup :)

    Dave
     
  16. pizoman

    pizoman

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    Mar 10, 2012
    The 9 Volt battery is on the other side of the board. The regulator I'm pretty sure is correct, from left to right Vin, Vout, Adj.

    [​IMG]
     
    Last edited: Feb 10, 2013
  17. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    OK, it's possible that the regulator needs to be lightly loaded or the output voltage will float high.

    Try placing a 1k resistor across the output (something between about 220 ohms to 1k should be fine. Normally the voltage divider serves this function.
     
  18. EinarA

    EinarA

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    Feb 11, 2013
    My guess would be the regulator is dead.
     
  19. davenn

    davenn Moderator

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    Sep 5, 2009
    No your regulator pin conns are still incorrect
    LOOK at the drawing I did the alterations on for you
    left to right Adj Out In

    this info is readily available in the datasheet for the device
    maybe you need to google that ;)

    Dave
     
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