homemade battery powered usb supply

Discussion in 'The Projects Forum' started by lokeycmos, Dec 2, 2011.

  1. lokeycmos

    Thread Starter Active Member

    Apr 3, 2009
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    hello, i just got a bright idea the other day. i want to make a portable battery powered USB supply to power my friends E-Cigarrette on the go. i drew up a quick schematic, just need some critiques before i build it. it looks right to me, but would like your opinion before i put it together. ty
     
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  2. wayneh

    Expert

    Sep 9, 2010
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    That'll work, but realize that 4/9 of what the battery supplies will be burnt off as heat, and that a 9V battery just doesn't have much juice to begin with. Under much load at all, it won't even be able to hold 5V at the output because there's some drop across the regulator itself and the battery will be pulled down to 7V or below. You might consider 4 AAs and drop the regulator, or use a 12v supply in the car.
     
  3. lokeycmos

    Thread Starter Active Member

    Apr 3, 2009
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    ooohh. how much drop are we talking across the regulator?
     
  4. wayneh

    Expert

    Sep 9, 2010
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    The datasheet says it needs 7.2v minimum to maintain regulation at 0.5A. At 0.5A, the 9V battery will not supply 7.2v.

    On the upside, I don't think you need the capacitors when battery-operated.
     
  5. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,871
    1,394
    Three AA or AAA batteries in series will do the job without any other components except the USB jack. And they will last a lot longer than a standard 9V battery.
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Cool Solution

    She created the "Minty Boost" boost converter about 3 or 4 years ago, and now it's almost a household name.

    Duracell and Energizer have even put out clones.
     
  7. lokeycmos

    Thread Starter Active Member

    Apr 3, 2009
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  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Yes, it makes the schematic a little easier to follow simply noting frequently used common lines (if done properly).

    Circuit board is only $5, so if you order that and the switching IC, it would save a lot of time. Though you could order the switching IC and the rest of the stuff needed at the same time you get parts for your amp and save a lot on shipping as well.
     
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