Center-tapped transformer versus Bridge Rectifier

Discussion in 'General Electronics Chat' started by djsfantasi, Jul 27, 2012.

  1. djsfantasi

    Thread Starter AAC Fanatic!

    Apr 11, 2010
    I see in many posts, people asking about power supplies. Some responses use a bridge rectifier after the transformer and some use a center-tapped transformer and two diodes. I understand how to select the required secondary voltage of the transformers in these two options.

    My question is, what are the pros and cons of either method? I always have used a bridge rectifier...
  2. wmodavis

    Distinguished Member

    Oct 23, 2010
    "My question is, what are the pros and cons of either method? I always have used a bridge rectifier... "

    A PS with non-center tapped transformer has the advantage of not needing a center tap (which is a more complicated and difficult to manufacturer). Though, I would add, 'not much so'. It does add extra steps in the process.
    The Bridge circuit required 4 diodes as opposed to 2. A disadvantage because of two additional components and one additional diode voltage drop which the transformer may need to make up for by supplying more voltage.

    This is not necessarily all of the pros & cons.
  3. bountyhunter

    Well-Known Member

    Sep 7, 2009
    FWB better utilizes the transformer secondary winding: in the FWB, the xformer secondary current is around 1.8X times the DC load current. FWCT it's about 1.2X DC load current, but the FWB gets twice the voltage so you can use a smaller transformer with a lower VA rating to get a specific amount of load power.
    PackratKing likes this.
  4. gerty

    AAC Fanatic!

    Aug 30, 2007
    PackratKing and #12 like this.
  5. #12


    Nov 30, 2010
    Great reference material, gerty. The point bountyhunter was describing is that the whole secondary is delivering power with every pulse so the winding is better utilized with a FWB. With the 2 diode setup, half the secondary is not delivering power, half the time. That costs you more $$ for the correct transformer.
  6. bountyhunter

    Well-Known Member

    Sep 7, 2009
    In most cases, the FWCT is only justifiable in cases where the output voltage is low and the power saving of a diode drop in the current path more than makes up for the "wasted" power lost in the transformer.
  7. creakndale

    Active Member

    Mar 13, 2009
    If you want positive AND negative voltage(s) from your power supply, I'd use a center tapped transformer.

  8. PackratKing

    Well-Known Member

    Jul 13, 2008
    I'm prejudiced towards the large square monolithic bridges, just because you can bolt them to a heatsink that reflects intended use, and include a 2" sq. pancake fan [ my bend toward overkill again :rolleyes: ] if you really expect to try and make it break a sweat.....:D

    The layout lends itself easily to a whole lot of design options.
  9. K7GUH


    Jan 28, 2011
    I favor a FW bridge and a center tapped transformer. In tube type gear, we used the lower voltage off the center tap for B+ to the exciter and/or receiver, the top end of the bridge for B++ to the PA stage.