How to build SMPS ac to dc

Discussion in 'The Projects Forum' started by johnsorious, May 20, 2015.

  1. johnsorious

    Thread Starter New Member

    May 20, 2015
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    I need to build a SMPS for a project. It needs to be 120V AC to dual outputs of 5V DC. I have no clue where to start. I'm just looking to build a very simple SMPS. Can someone point me into the right direction?
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    What is the current requirements of the 5V outputs?
    Look below at Similar Threads, Building a simple SMPS. Might get some ideas from this old post.
     
  3. johnsorious

    Thread Starter New Member

    May 20, 2015
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    I actually don't have any requirements for it. If it's important I would say 1A each since I'm only powering some pic chips and logic gates.
     
  4. tcmtech

    Well-Known Member

    Nov 4, 2013
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    You will never build one smaller cheaper or more reliable than you can buy one disguised as a common USB type charger.
     
  5. johnsorious

    Thread Starter New Member

    May 20, 2015
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    I need to custom make one for a school project.
     
  6. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    A mains powered SMPS is hardly suitable as a school project for someone with "no clue where to start"; 170VDC is not for the inexperienced.
     
    Last edited: May 21, 2015
  7. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    trust me mate, you won't do it,too much hassle and cost, an ordinary mobile phone charger will give 5V @ 1amp, plenty on the internet......
     
  8. DickCappels

    Moderator

    Aug 21, 2008
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    You are not getting a lot of encouragement to jump into a power supply that runs from the AC mains because from your post, you have not had experience in this area, and such a design could be dangerous even with the requisite experience and test equipment.

    Would a transformer-isolated power supply (step-down transformer, rectifier, capacitor) followed by a switching regulator (such as a National/TI simple switcher) qualify? A friend of mine with little analog experience did that with only a DVM as test equipment.

    https://www.ti.com/ww/en/simple_switcher/regulators.html
     
    Last edited: May 21, 2015
  9. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    If this is a school assignment, then the parameters might be firm/fixed. If so, look into Power Integrations. They are the industry leader in low power off-line switchers, and are in 75% of the USB wall-warts out there.

    The biggest problem in any switching power supply task is the magnetics, usually a transformer. I agree with DC - the easier way to go, if allowed, is to build a linear bulk supply followed by a switching regulator.

    ak
     
  10. tcmtech

    Well-Known Member

    Nov 4, 2013
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    The easiest cheat on this would be to find a older computer power supply or other electronics device that was built before surface mount designs became common and stirp the parts from the small independant 5 volt SMPS part of the unit that was used for standby power and rebuild it on your own circuit board.

    Those power supplies were fairly simple and did not have a large part count or difficult to trace circuit board layout which would make them ideal for a DIY SMPS type project.

    That way you would have the correct schematic components and a fairly guaranteed likelihood of it actually working the right way the first time provided you correctly copied and transferred everything.
     
  11. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    I would go with DC's #8 post to avoid your post from violating the AAC Terms of Service prohibiting line operated circuits without isolation.
    Look up Flyback Converters For Dummies, basically lo V to high V, but instructive. http://www.dos4ever.com/flyback/flyback.html.
     
  12. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Isn't that what your teacher is for? :D

    teach·er
    ˈtēCHər/
    noun
    1. a person who teaches, especially in a school.
    teach
    tēCH/
    verb
    1. 1.
      show or explain to (someone) how to do something.
     
  13. tcmtech

    Well-Known Member

    Nov 4, 2013
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    I take it you are not familiar with how the public education systems works now.

    Teachers are now often times the last place you want to try and get any degree of useful help. :(
     
  14. johnsorious

    Thread Starter New Member

    May 20, 2015
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    I've taken an electronics course 1.5 years ago and we went over power supplies very briefly. I am looking for some help to building a simple one for part of a senior project.
     
  15. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    What have you got so far? Can you provide a block diagram of the main components of the SMPS you wish to design?
     
  16. ScottWang

    Moderator

    Aug 23, 2012
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    During the old time, almost everyone can build a linear power supply as AC110V/220V to 5Vdc/9Vdc/12Vdc, etc...

    Since the SMPS start to full of the market, and then the linear power supply only for the low ripple experiments, and to build a SMPS became an impossible mission, what is that cause this situation, the most important things is in the transformer, if we want to build a linear power supply then we could buy the transformers from the EE stores, but when we trying to build a SMPS, we can't get a appropriate transformer from the EE stores, and also we can't make one, unless to study a lots of theories and trying to make a lots of high frequency transformers to try, so today just a few people to DIY the SMPS, and those people still have to overcome the hard time, if they can't conquer the difficult skills then when he get fail, maybe they won't try again, SMPS, need money, need equipment, need time and be patience, otherwise it won't work normally.
     
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