Get a 18VDC and 12VDC from a single center tapped transformer

Discussion in 'The Projects Forum' started by falblambiz, Aug 3, 2010.

  1. falblambiz

    Thread Starter New Member

    Oct 31, 2007
    5
    0
    Hi. I was working on a class project and some parts of the schematic required a 18VDC regulated voltage and the other partes required a 12VDC regulated voltage and I have a 120VAC to 18VAC center center tapped transformer (so I have two 9VAC outputs) (see image posted below). My question is: instead of using two separate transformers, can i connect one circuit to the 18VAC (using the two side wires) and the other circuit to 9VAC (using the center wire and a side wire)? is there any misunderstood concept that may limit that kind of configuration?

    P.D.: Current consumption is not a problem because the sum of both circuits' consumption is about 800mA. Also, I understand the concept of RMS and that's the reason I know i can obtain 12VDC from a 9VAC RMS output.

    Thanks in advance!
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    Yes it will work- but there is no common ground & the 12V is about 11V, not highenough to feed a regulator. Howabout using one bridge & feed two regulators- depending on expected load. Could use a buck convertor for the 12V if efficiency is important.
     
  3. falblambiz

    Thread Starter New Member

    Oct 31, 2007
    5
    0
    I didn't think of the two regulators solution for being a newbie and that seems to work for my project. Thanks!.

    Anyway just out of curiosity and for conceptual clarity: if I add a common ground to the outputs like the image that i attached here, will it work?
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    Without a fuse in the primary,I would not try it just to see which item blew first.
     
  5. falblambiz

    Thread Starter New Member

    Oct 31, 2007
    5
    0
    Haha, that's all I needed to hear... thanks a lot.
     
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    Look closely at how the current would flow through the bridges should you insert a common ground that way.

    Is there any reason you can't just rectify the 18V then have separate 18V and 12V regulators?
     
Loading...