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How does an ATX power supply work?

Discussion in 'Power Electronics' started by MrOmnos, Jun 13, 2015.

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  1. MrOmnos


    Jun 4, 2014
    I was looking to build a bench power supply. So, I broke into an old ATX power supply to salvage parts. I found 3 power transistors [KSE13009L], and 3 schottky barrier rectifiers [S30D40C] but I didn't find any voltage regulators which I was hoping to find. I did find a packaged Bridge Rectifier though which will come in handy. And a KA7500B smps controller chip. I don't understand how the power supply manages to give out 5, 12 and 3.3 volts without any voltage regulators ics like LM7805 ?
  2. Martaine2005


    May 12, 2015
    I think most ATX psu's use components to achieve the different voltages rather than dedicated regulators.
    The KA7500B (switched mode power supply controller) is in fact a 5 volt regulator (or 5 volt reference) Or 5 volt standby for the motherboard.
    This 5 volts is converted to 3.3 volts using components (not a regulator).
    Once the psu's POST has completed it will (allow) the 12 volt to be present by components (not a regualator).
    I think that if REGULATORS were used, the transformer would be quite hefty.
    So the three transistors are probabaly for the 3.3v, 5v and 12v..
    I am not saying how they work!!
    Just my assumption.
  3. ramussons


    Jun 10, 2014
    You may not have to breakup a ATX PSU to make a bench supply.
    Google and you may get an idea that suits your requirement.
  4. BobK


    Jan 5, 2010
    It is a switch mode power supply, so you will not find any linear regulators in it. Typically, they use a transformer with multiple windings to get the various output voltages. One voltage is regulated, and the others are simply based on the ratio of turns in their windings.

  5. MrOmnos


    Jun 4, 2014
    I was just trying to salvage usable parts. But now I have learned alot about SMPS and may be I'll be build one in coming future.
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