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5v SMPS power supply from 220v mains

Discussion in 'Power Electronics' started by roltex_rohit123, May 16, 2010.

  1. roltex_rohit123

    roltex_rohit123

    92
    0
    Oct 12, 2009
    I want to design a 5v 1A SMPS power supply from a 220v mains supply. I dont have much idea of the circuit and how it works. I once opened a small unit and saw that AC mains was rectified and and through a 20 ohm resistor fed to a small SMPS transformer and through an optocoupler the output was given. can anyone help me in building one?
     
  2. davenn

    davenn Moderator

    13,294
    1,758
    Sep 5, 2009
    not quite like that... the rectified mains voltage ~ 300VDC give or take a bit is then
    through one of the primary windings of the transformer and through a hi freq switching transistor (what they often call a chopper transistor) oscillating/switching ~ 1 to 3KHz region. That higher freq means the transformer can be much smaller than a normal linear PSU where the mains AC voltage is at 50 or 60 Hz (depending on your country).

    the output off the secondary winding/s goes through fast recovery diodes smoothed,regulated and sent to output cable.
    NOTE the opto-coupler is usually between the secondary and primary sides... it provides feedback to the HV switching side.

    still a relatively basic description,but fills in a few more gaps for you.

    It is probably cheaper and DEFINATELY SAFER to spend $20 on a 5V SMPS plugpack from your local electronics store than buying the parts and trying to build one

    Unless you have worked with high voltage and very familiar with such ccts, I wouldnt recommend you playing with such PSU's

    cheers
    Dave
     
  3. 55pilot

    55pilot

    434
    3
    Feb 23, 2010
    What's the matter? Your plans involving molten lead and oxygen are no longer a good enough method for killing yourself?

    ---55p
     
  4. roltex_rohit123

    roltex_rohit123

    92
    0
    Oct 12, 2009
    no i've got cyanide!!! lol..
     
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