Flyback DC-DC converter Design

Discussion in 'The Projects Forum' started by Abel Assegid, Mar 18, 2010.

  1. Abel Assegid

    Thread Starter Member

    Nov 5, 2007
    I was working on a flyback SMPS with LT3573 which is an isolated flyback controller which drives it feedback information form the reflected output voltage(Flyback Pulse). The following equation relates the output to the flyback pulse:
    V(Flyback)=Turn_Ratio*(Vout + Diode_Drop)
    But I want to have two outputs( 5V and 15V). How can I relate the two outputs to the flyback pulse(reflected voltage)? Help please.
    Last edited: Mar 18, 2010
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
    If possible, add a tap on secondary or add a 5V winding.
  3. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    Add another secondary, with the turns calculated from the existing secondary turns and the ratio of that voltage to the new output, allowing for diode drops.

    eg. if you have a 5V output with 9 turns, call it 5.5 before rectification;
    9 / 5.5 x 12.5 = 20.45 turns, round to 20.5
    That should give 12.5, then less a diode drop = 12V.
    (I'm assuming schottky diodes).

    It will be a bit of trial and error to adjust for the loads on the windings, as the feedbck is indirect.
  4. Abel Assegid

    Thread Starter Member

    Nov 5, 2007
    Thanks for replying.
    But my question was to detemint the reflected output voltage at the primery when we have more than one output.