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looking for 110/120vac to 5vdc power supply schematics

Discussion in 'Power Electronics' started by dcoultas, Apr 29, 2010.

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  1. dcoultas

    dcoultas

    9
    0
    Apr 24, 2010
    I am looking for schematics for a 110/120vac to 5vdc switching power supply. It only needs to be 3A max at output. If anyone has a schematic or knows where to find one your help would be much appreciated.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,452
    2,812
    Jan 21, 2010
    can you first explain why the results of googling for "5v 3a switching power supply schematic" were insufficient?
     
  3. 55pilot

    55pilot

    434
    3
    Feb 23, 2010
    And after you locate the schematics, the next question is, why do you want to do it this way rather than buying a 5V power supply?

    Working with 110V is dangerous. Are you qualified to be working with it? Depending upon where you are located, there may be regulatory requirements for anything you plug into the wall outlet and the power supply you make is unlikely to meet them.

    ---55p
     
  4. dcoultas

    dcoultas

    9
    0
    Apr 24, 2010
    The main reason I want to build one is to learn and to experiment with. I looked for quite a while on google and could not find what I needed. If someone knows where I can buy the power supply I need for cheap that would also work.
     
  5. Tesla

    Tesla

    165
    2
    May 10, 2010
    Any cheap PC power supply will work. You also get 12v and some others. Any old PC you or a relative has in their closet will likely work fine.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    SMPS are really bad things to try to learn from -- other than to learn not to play with them.

    If you want to learn, building a linear power supply will teach you a lot more.

    What have you built before? What is your level of experience with electronics?
     
  7. roltex_rohit123

    roltex_rohit123

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    0
    Oct 12, 2009
    a linear power supply is quite easy to make. but SMPS is something new and goodto play with. I'm also trying to build one. Linear power supply has a limitation tha the transformer gets hot in an hour of full load and then it is not suitable to handle. it starts smelling burnt and sometimes goes off. but SMPS is nt like that. i keep my modem working day and night and the SMPS adaptor doesnt get hot at all. just warms a bit. this must also be saving a lot of energy.
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,452
    2,812
    Jan 21, 2010
    If your transformer (I presume wall wart) gets that hot, then it is underrated.

    If you are really keen on building a SMPS then I would advise starting with (say) a 12V transformer and building a buck regulator to reduce that to 5V.

    The advantages are safety (both for you and your equipment) and the ability to use off-the-shelf inductors.

    The design issues are similar but you don't have to play about with rectified mains.

    If something goes wrong, you have a far smaller chance that smoke will erupt from multiple places.

    You're right about SMPS, it's far less likely to get hot and smoke during actual use. But it's far more likely to get hot and smoke during development.

    Depending on your device, the regulator may not be that much more efficient. As an example I have a device that claims to require 12VDC, however others that have opened them up have found it contains it's own switchmode regulator producing 3.3VDC. It has been found that any input voltage from 5 to 16V (the capacitors are rated for 16V, the regulator apparently up to some higher value) will work fine. On that basis, a carefully designed 12V SMPS is likely to be less efficient than a simple unregulated DC supply providing a nominal (say) 10VDC.

    The previous point indicates that you need to be aware of your load in making PSU decisions.
     
  9. 55pilot

    55pilot

    434
    3
    Feb 23, 2010
    A SMPS is neither new nor it is good thing to PLAY with for a person of any skill level, especially a beginner. If you happen to have a desire to kill yourself, that is your problem. Encouraging others to do so is criminally irresponsible.

    For a mains connected power supply:

    If you have a known and stable input voltage, a linear power supply can be fairly efficient. If your linear power supply is getting hot, you are either drawing more current from it than it is rated for, running it at a higher input voltage than it is rated for, or it is a horribly bad design. If you want to deal with a large range of input voltages, you need a switcher supply. Designing a switch mode power supply is non trivial. It is not something you ought to be "playing" with. Because of the difficulty and risks, it is certainly not something for hobbyists

    For a low voltage DC to another low voltage DC power supply:

    A linear power supply can be fairly inefficient if the currents involved exceed a few milliamps. A DC-DC converter can be much more efficient. In the hands of an experienced designer, under reasonably constrained conditions, 95% or higher efficiency is possible. An inexperienced person will require quite a bit of reading and understanding to produce a half way decent design. It will require experience to be able to design a DC-DC converter that works well. There is no getting around that. You can not breadboard a DC-DC converter, so the ability to fabricate PC boards is absolutely essential. In order to learn what is going on in the power supply, access to a decent scope is essential. If you really want to learn, an AC current probe is also required.

    Once you have become proficient with low voltage DC-DC converters, you can try and design a high voltage one.

    ---55p
     
    Last edited: May 17, 2010
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