Help with power source

Discussion in 'General Electronics Chat' started by art_12345, Mar 26, 2015.

  1. art_12345

    Thread Starter New Member

    Mar 26, 2015
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    Hi, I am new to this forum, and also I want to apologize for my bad english.
    I am trying to buil a power source where I can get +12v dc, -12v dc, 5vdc, and a full rectified signal of 12v like the following:
    [​IMG]

    I am using a transformer with central tap and the following circuit to get all the dc voltages:
    aa.jpg

    but I want to know if there is a way to get also the full rectified signal without using another transformer?
     
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  2. Papabravo

    Expert

    Feb 24, 2006
    10,157
    1,795
    Once the capacitors are placed on the output of the bridge rectifier the rectified AC is GONE.
    You can run the output of the +12v to a 7805. If you pull significant current it will get very hot according to
    (12V - 5V)* (0.5 Ampere) ≈ 3.5 Watts

    A better solution is a multitap secondary or a third secondary winding.
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    xf.gif
     
    Last edited: Mar 26, 2015
    art_12345 and cmartinez like this.
  4. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Bullseye Mike... I was trying to solve the OP's conondrum, until I saw your post.... it's met all of the KISS's requirements...
    @art_12345, the full answer is in Mike's post.
     
  5. ScottWang

    Moderator

    Aug 23, 2012
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    If the D5,D6,R4 used for the input of 5V regulator, do you think is that too high?
     
  6. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    The standard 7805 can handle up to 35V, I think. So he should be alright.
     
  7. ScottWang

    Moderator

    Aug 23, 2012
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    20Vac is too high for a liear 7812,7912 regulator.
    I'm not talking about input rated voltage, it should care about the power consumption of 7805, when the input voltage is too high then all the waste power will turn to the heat in the 7805, it may reducing the using life of 7805.
     
  8. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Oh... I think I understand now. The 7805 is a linear regulator, so maybe he should be using a switching one instead?
     
  9. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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  10. art_12345

    Thread Starter New Member

    Mar 26, 2015
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    Thanks Mike, this is what I was looking for, I will change the7812 for the switching regulator also, Thanks to all
     
  11. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Yes, the same brand I posted handles the same switching regulator at other voltages. Just check it out.
     
  12. ScottWang

    Moderator

    Aug 23, 2012
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  13. ScottWang

    Moderator

    Aug 23, 2012
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    I just checked the R-78C5.0-1.0 online store in Taiwan, only one I can find and it charges NT$350 close to US$11.17, wow, it can be buy a small arduino to play.
     
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