Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Switch mode power supplies

  1. Aug 1, 2006 #1
    Hi there,

    I'd like to switch 220-250v AC (50/60Hz) to 5 or 3.3v DC as easily and in the physically smallest way possible. Can someone offer advice on this? Do there exist IC's that will just do this for me? I have experience with LSR's but a transformer is too bulky for my needs.

    Thanks!
     
  2. jcsd
  3. Aug 1, 2006 #2

    Danger

    User Avatar
    Gold Member

    Don't they have wall adapters where you are, such as are used for laptops or such? Do you mean that one of those is too bulky?
     
  4. Aug 1, 2006 #3
    How much current do you need out of it? If it's a very small amount, you can use a small transformer and get your desired voltage. As for switch mode supplies, they are a lot more complicated than a normal linear supply but still use a transformer. A switch mode supply in a nutshell takes the 60hz ac current, converts it to 30khz pulsating DC current and then transforms and filters it to pure DC. The secret is being able to make the current into a very high frequency which allows you to transform the same amount of power of a regular supply, but with a smaller transformer and caps.
     
  5. Aug 1, 2006 #4
    haha! yes... laptop thing is a bit too bulky...

    i'm looking for this to include in a design that will hopefully fit in that small gap in the concrete behind a lightswitch... wait..... if you're an american with those woody housey things, let me explain....

    real houses are built of bricks... its like a square stone thing... you pile a bunch of them together & stick them together with a kind of glue we call concrete... like a sand-glue stuff... its all really cool... doesnt burn down or get blown over by the wind.. u guys should try it!

    there's typically a small space behind a lightswitch for excess cable or whatever... and i want it to sit in there without causing too much heat... but, no, i'm not using lots of current... its just to power a uController basically... so really, 10mA is more than enough.

    can a powersupply be made that small?

    thanks again :) sorry for patronising the yanks :p
     
  6. Aug 1, 2006 #5

    berkeman

    User Avatar

    Staff: Mentor

    There are some very tiny switching wall transformer-type power supplies available now. The market has been driven by USB and Ethernet hubs and such things. I've seen ones that are only a couple cm on a side, delivering an amp or so at 5V, with universal 100-240VAC input capability. I did a quick google search and didn't find any great pictures, but this will give you an idea:

    http://www.am-transformers.com/products2/switchmode.html

    Just do a bit of googling to see how small you can find them. Even places like Digikey.com and Mouser.com have them.
     
  7. Aug 1, 2006 #6

    Danger

    User Avatar
    Gold Member

    Go ahead; I'm a Canuk. :biggrin:
     
  8. Aug 1, 2006 #7

    berkeman

    User Avatar

    Staff: Mentor

    Another option, Juming, would be to make your own "Energy Storage" power supply. Since you only need a few mA, you can use a simple HV capacitor as the isolating/dropping element from your 240Vrms mains. You can read more about them starting on page 158 in a document from my company's website, "PL 3120 / PL 3150 Smart Transceiver Data Book", which is document 005-0154-01 on this page:

    http://www.echelon.com/support/documentation/manuals/transceivers/

    BTW, you will need to get your devices safety approved if you want to be installing them in real houses. I believe the agency is TUV in the EU, but I'm not sure. If you use the pre-built units that I mentioned above, they come with their own safety agency approvals. If you build your own, you really should get them safety approved. Maybe bricks don't burn, but the wall material inside the house does, and if your devices start a fire, that would be bad. Also, you really should only tackle building things that connect to the AC mains if you have experience with working with high voltages. The AC mains is dangerous when it's exposed, and it's easy to get hurt or blow up test equipment if you don't have the experience yet. Stay safe!
     
    Last edited: Aug 1, 2006
  9. Aug 2, 2006 #8
    What better time to start than now!!! :) that's why I was looking for the easiest & smallest solution to quickly bring the AC mains to a 5V DC that I know! :)

    how about this... is this feasible:
    If i use a rechargable battery & then somehow inductively couple power from the mains line when it is on to trickle charge the battery?
    would that even work? if so, how?

    thanks for your help :)
     
  10. Aug 2, 2006 #9
    Google says Canuk = Central Association for Nigerians in the UK ... ???

    :tongue2:
     
  11. Aug 2, 2006 #10

    Danger

    User Avatar
    Gold Member

    That's why one should never trust the net as a definitive source. I'm Canadian. :rolleyes:
     
  12. Aug 2, 2006 #11
    I am also from Canukistan too! :biggrin:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Switch mode power supplies
  1. Power Supply (Replies: 8)

  2. Power Supply (Replies: 4)

  3. Power supply (Replies: 5)

Loading...