looking for 5 Volts powersupply schematic

Discussion in 'The Projects Forum' started by benjazzy, Apr 1, 2010.

  1. benjazzy

    Thread Starter New Member

    Apr 1, 2010
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    0
    how about converting and stepping the 120 ac volt down to 5 dc volt. how can i do it
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    For starters, you need a suitable transformer. If you are in the USA, you can get a transformer from your local Radio Shack store. You'll also need a power cord and project enclosure box.

    The transformer will need to have a suitable voltage and current rating. You should use a 1A fuse between mains power and the transformer. You can add a switch after the fuse, if you would like.

    Then you will need to rectify the AC into rippled DC using diodes or a rectifier bridge.

    Rather than purchasing a transformer and cord, you could use a "wall wart" plug supply. You probably have some of these around the house already. They generally output a rippled DC voltage.

    You will need (a) large filter capacitor(s) to remove most of the ripple from the DC.

    Then you will need some sort of voltage regulator. A 7805 is an easy-to-use 5v regulator IC. It has three terminals; IN, OUT, and GND. You will need a heat sink for it.

    You will also need an 0.33uF cap on the input of the 7805 to ground, and a 0.1uF cap from the output to ground. If you do not include these last two capacitors, the regulator might oscillate at high frequency.
     
  4. Tahmid

    Active Member

    Jul 2, 2008
    344
    25
    Hi,
    The basic idea is:
    120vac ----> fuse ---> transformer ---> rectifier(bridge rectifier or full wave) ---> bulk capacitor (1000uF) ---> decoupling cap (0.1uF) ---> regulator (7805) ---> bulk capacitor (220uF) ----> decoupling cap (0.1uF) ---> load

    Take a look at these for reference:
    http://www.aaroncake.net/circuits/supply6.asp
    http://www.epanorama.net/circuits/vga2tv/psu_5v.html
    http://www.electronics-project-design.com/DCPowerSupply.html
    http://en.wikipedia.org/wiki/Diode_bridge
    http://www.play-hookey.com/ac_theory/ps_rectifiers.html
    http://web.njit.edu/~mlh3/procedures.pdf

    Hope this helps.
    Tahmid.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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