Help Building PSU

Discussion in 'The Projects Forum' started by MrYu, Aug 5, 2012.

  1. MrYu

    Thread Starter Member

    Sep 26, 2011
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    hi how to make PSU that can output 12v and 5v dc? tnx
     
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Get an old computer power supply.
     
  3. MrYu

    Thread Starter Member

    Sep 26, 2011
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    i want to build with my own do you have a circuit which it can output 12 and 5v or what kind of transformer i will use, connection and components tnx
     
  4. bertus

    Administrator

    Apr 5, 2008
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  5. MrYu

    Thread Starter Member

    Sep 26, 2011
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    For the Uc it must be 5v and for relays is 12v,. i'm planning to build one for my project. i don't like to buy a ready made coz i will not understand how the circuit of a psu works.
     
  6. MrYu

    Thread Starter Member

    Sep 26, 2011
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    i made a simulation which is 220v for source and i set it to 60hz,. i only get 11.2v for 7812 regulator
     
    Last edited: Jan 20, 2013
  7. absf

    Senior Member

    Dec 29, 2010
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    Normally it's difficult to simulate transformers in proteus. If you put a voltmeter before the 7812, what voltage do you get?

    Allen
     
  8. MrYu

    Thread Starter Member

    Sep 26, 2011
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    i get 12.2 to 12.3v it's unregulated
     
  9. absf

    Senior Member

    Dec 29, 2010
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    You need at least 14.5V of unregulated input in order to get 12V output. Look at the datasheet attached.

    Allen
     
  10. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You have wired the diode bridge wrongly.
    The top wire of the transformer should go between D1 and D3.

    Bertus
     
  11. absf

    Senior Member

    Dec 29, 2010
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    Yes, you're right. I didn't notice it at the first glance. Need a cup of black coffee, I guess....:D

    Allen
     
  12. MrYu

    Thread Starter Member

    Sep 26, 2011
    42
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    i made another circuit do you think this will work in real life when i build this.
    just curious the voltage before the 7812 is too high
     
    Last edited: Jan 20, 2013
  13. absf

    Senior Member

    Dec 29, 2010
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    Assuming the voltage after the rectifier is 15V. If the output current of 7805 is 800mA, then 10V is dropped across R1 10Ω resistor dissipating 8W. It would be quite hot.

    The rest seems OK, but why did you parallel 2 x 1N5402 for each branch? One on each branch should be adequate.

    Allen
     
  14. MrYu

    Thread Starter Member

    Sep 26, 2011
    42
    0
    how to configure this in trafo or the alternator. i get 50v before the voltage regulator 7812/7805?
     
    Last edited: Aug 14, 2012
  15. MrYu

    Thread Starter Member

    Sep 26, 2011
    42
    0
    up......................
     
    Last edited: Aug 14, 2012
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