+/- 5V Power Supply

Discussion in 'General Electronics Chat' started by Peytonator, Mar 29, 2010.

  1. Peytonator

    Thread Starter Active Member

    Jun 30, 2008
    105
    3
    Hi there,

    I am wanting to make a +/- 5V power supply, but need a centre tap transformer (I think!) -- similar to the following design:
    http://www.reconnsworld.com/power/multipowersupply.gif

    The only problem is that I don't have a centre tap transformer, but just a normal two-winding step down transformer.

    • Is it possible to use a normal transformer as a centre tap transformer? Or how else can I get -5V out?
    • Also, is the 100uF cap on the output neccessary?
    Thanks :)

    Edit: another question on the side:
    If I have a raw signal of about 0.1-1uV coming in to a band pass filter, is it better to amplify it (by about 1000) before or after the filter?
     
    Last edited: Mar 29, 2010
  2. russ_hensel

    Well-Known Member

    Jan 11, 2009
    818
    47
    No need for ct, just use half wave rectification with one end of the transformer ground. Each diode ( 2 ) points in the opposite direction ( conventional current flow ).
     
  3. Peytonator

    Thread Starter Active Member

    Jun 30, 2008
    105
    3
    Sorry ... I'm lost :/ How do you get +/- 5V from that?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    See the attached schematic.

    If you wish, you can add a 10uF capacitor to the outputs of each regulator. This will help to improve transient response.

    C1 and C2 are very minimal. I suggest doubling their size.

    If your load requirements are small, you could substitute 1N400x diodes for the 1N540x diodes.

    As far as your 2nd question, please start a new thread with a suitable subject line; you will receive much better help that way.
     
  5. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    Take warning that the pinouts for 7805 and 7905 regulators are different so their respective wiring will be different.
     
  6. Peytonator

    Thread Starter Active Member

    Jun 30, 2008
    105
    3
    Thanks so much for your help. Problem solved! :) :)
     
  7. rvh002@gmail.com

    Active Member

    May 15, 2009
    118
    2
    Your C2 in the dwg, seems to be upside down
     
  8. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Well spotted that Wildebeast.
     
  9. rvh002@gmail.com

    Active Member

    May 15, 2009
    118
    2
    Actually an Eland , about the weight of an American buffalo.(Big grin)
     
  10. studiot

    AAC Fanatic!

    Nov 9, 2007
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    I stand corrected.
    I will take my demerits along with Wookie.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    You are correct on that point.

    Thank you for pointing out the error.
     
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