12V/24V simultaneously from 12-0-12

Discussion in 'The Projects Forum' started by abuhafss, Aug 26, 2013.

  1. abuhafss

    Thread Starter Active Member

    Aug 17, 2010
    148
    2
    I am considering to use a center-tapped 12-0-12 (A-C-B) transformer for getting 12V and 24V simultaneously.

    I tried to use one bridge across A and C to get 12V, and another across A and B to get 24V. But when the two negatives are connected, both outputs become 24V.

    Any help shall be appreciated.
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,653
    632
    I assume that you want positive voltages, but this method will work to get ±12 and ±24 VDC.

    You can ground one end of the winding, then use the center tap to drive a rectifier for your 12 volt output, then rectify the end of the winding to get 24 volts.

    This only gives you half-wave rectification so you will need a larger capacitor for a given amount of ripple at a given load, and you won't be able to get as much current out of the transformer as with full wave rectification.
    [​IMG][​IMG]
    http://postimg.org/image/l28psk007/

    You probably don't want all the outputs, so just leave off the diode and capacitor for each output you won't want.
    [​IMG]
     
  3. abuhafss

    Thread Starter Active Member

    Aug 17, 2010
    148
    2
    Thanks for your response.

    How about this circuit in terms of current drawing from the transformer?
     
  4. DickCappels

    Moderator

    Aug 21, 2008
    2,653
    632
    I am not familiar with this arrangement, but it appears to be a fully wave voltage doubler. It will still subject the transformer to a high peak/average current and it might be better than the half wave rectifiers. In other words, I don't know. How about simulating the two configurations with SPICE and comparing them? That's one thing that SPICE is pretty good at doing.
     
  5. #12

    Expert

    Nov 30, 2010
    16,292
    6,804
    Regarde...
     
    Last edited: Aug 28, 2013
  6. abuhafss

    Thread Starter Active Member

    Aug 17, 2010
    148
    2
    With LTSpice, your configuration gives 12V and 24V whereas, my configuration gives 12V and 33V. With Falstad's java simulator both gives 12V and 24.

    #12's last circuit almost similar to mine. seems to be better.
     
    Last edited: Aug 28, 2013
  7. abuhafss

    Thread Starter Active Member

    Aug 17, 2010
    148
    2
    Thank you.
     
  8. #12

    Expert

    Nov 30, 2010
    16,292
    6,804
    It's a matter of slowly stepping through the additions to be sure you got the grounds right.

    I got some sort of brain failure looking at your circuit so I just backed up to basics.
     
  9. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    Hi abuhafuss,

    You do realize that if you half-wave rectify 12 vac for example and add a filter capacitor you will get roughly the peak AC voltage out minus the diode drop, (and ripple), correct ?
     
    Last edited: Aug 28, 2013
  10. abuhafss

    Thread Starter Active Member

    Aug 17, 2010
    148
    2
    Yes, I am getting 11.45V and 22.90V.
     
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