Stepping down 20v/3.25A into 12v/2A and 5v/1A

Discussion in 'The Projects Forum' started by navdroid, Jul 19, 2013.

  1. navdroid

    Thread Starter New Member

    Jul 19, 2013
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    Hi All,

    Can someone please help in my project? I have a laptop power supply which I would like to use to power a raspberry pi and a LCD screen. The raspberry pi takes 5v/1A and LCD screen controller board takes 12v/2A. I would like to power both using only one power supply, so will need to reduce the voltage down the line before it goes to respective devices.

    I checked switching controllers and voltage converter ICs but my knowledge about these things is very basic. Also, I heard it generates lot of heat.

    Can someone please advice if I can achieve step-down of voltage using good old color coded resistors? if yes, how can I calculate which resistor I need?:confused:
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    No, you will need voltage regulators. In addition, your power requirements seem too large for the devices. The RP model A needs 300mA or less, and I am doubtful about an LCD that requires 12V at 2A.
     
  3. navdroid

    Thread Starter New Member

    Jul 19, 2013
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    Thanks for your reply.

    The power requirements are confirmed. The LCD controller board powers up a 15.6" laptop screen and requires min of 2A current. Also, RPi needs min of 750mA current otherwise it starts hanging on applications.
     
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    http://www.ebay.com/itm/PM7-HOT-DC-...ravel_Adapters_Converters&hash=item35c9b76af5

    http://www.ebay.com/itm/AC-100V-240...=US_Server_Power_Supplies&hash=item3a7a976151
     
  5. navdroid

    Thread Starter New Member

    Jul 19, 2013
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    Thanks bounty hunter ut i would like to supply power using one power supply. Two power supply for a tablet wont be practical :)
     
  6. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Tablet? Like an iPad? They run on batteries and have touchscreens.
     
  7. navdroid

    Thread Starter New Member

    Jul 19, 2013
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    I agree but my project is to put a old laptop screen in a photo frame and power it using raspberry pi and use it as a digital photo frame or media device to play songs or other media content.......the device will sit on a desk or may be above a fireplace as a traditional photo frame
     
  8. navdroid

    Thread Starter New Member

    Jul 19, 2013
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  9. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Then why would you care if you plugged one cord or two into the wall?

    There are dual output supplies out there. Here's one for $6

    http://www.coolerstars.com/actodc12duou1.html
     
  10. absf

    Senior Member

    Dec 29, 2010
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  11. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Or, you can buy the one I posted for $6 that's a fully sealed plug in unit that has both converters in it.
     
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