Please help for this SMPS circuit

Discussion in 'General Electronics Chat' started by xyz9915, May 24, 2008.

  1. xyz9915

    Thread Starter Member

    Feb 24, 2008
    Hi! The attached file is a schematic of 50KHz SMPS power supply which uses 325 VDC (after rectification of Mains 240 V). The required current is approx 15 Amperes. Please give comment if any modification in the circuit is required.:confused::confused:
    • PS.pdf
      File size:
      64.8 KB
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    You've got 325Vdc pulses across your primary with an 8.9:1 turns ratio. Output will be 36.5Vpeak.

    Rectifier diodes in parallel don't work out so well. The one conducting the most current will heat up, and conduct more current, and heat more, and conduct more current, and let the smoke out of its belly. The others will suffer the same fate even more quickly. I strongly suggest using a pair of diodes able to handle 30Amps each.

    Q2 drain is not hooked up to anything. I presume you want it hooked to Q1 drain.

    Your MOSFETS will burn out. They'll need to handle a lot more than 106A, between them. They won't even be albe to handle 8A each unless you can liquid-cool them. See:

    The SG3525 is only able to source 100mA and sink 400mA. You are asking it to source and sink more than 500mA.

    Have you done the math to insure 500mA will be enough to turn off the IRF840s at your chosen 50KHz?
    Last edited: May 24, 2008
  3. S_lannan

    Active Member

    Jun 20, 2007
    In this type of configuration the mosfets will see 650vDC across them.
    Why so many primary turns on transformer? esr losses will be high.
    How did you calculate the snubbers on the transformer, they seem a little out as far as ballpark figures go.

    Datasheet says sg3525 can source and sink 500ma.