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5V output circuit

Discussion in 'Electronic Components' started by [email protected], Jul 24, 2006.

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  1. Guest

    Hi all,

    I need a basic circuit with an Output of 5V, It should run off two 1.5V
    AA batteries. Thanx!
     
  2. PeteS

    PeteS Guest

    Your homework assignment would probably have specified the output
    current required of this circuit. amongst other things (ripple, noise,
    step response to name but a few).

    Cheers

    PeteS
     
  3. Jamie

    Jamie Guest

    look for DC-DC converters.
    you can get them already made in mods..
     
  4. jasonbot

    jasonbot Guest

    I'm making a USB charger so I'm not to sure about all the deets All I
    know is that it should output 5V or else the device will blow..
     
  5. mc

    mc Guest

    How much current do you need to deliver?
     
  6. jasonbot

    jasonbot Guest

    No Idea, however much USB needs??? Think it's either 100 or 500mA
     
  7. jasonbot

    jasonbot Guest

    EDIT: device (iPod) needs 500mA of power 100mA is not enough to power
    it.
     
  8. Don Bowey

    Don Bowey Guest

    A correct USB port will source 500 mA.

    Don
     
  9. This is more complex than it seems. Any device that requires more than
    100mA, is meant to 'ask' the system if it can have the extra. Most USB
    ports _will_ supply 500mA, without such a request, but quite a few will
    give 'overcurrent' errors, if a device tries to draw this, without first
    getting the approval...

    Best Wishes
     
  10. jasonbot

    jasonbot Guest

    So the theory is there but what will the circuit diagram look like??
     
  11. mc

    mc Guest

    OK, you want 5 V at up to 500 mA from two AA cells. That will run down the
    AA cells fairly quickly, but not absurdly quickly... I don't know what the
    battery life will be.

    Since you're stepping up the voltage, this has to be a switching regulator,
    probably with an inductor (of carefully specified type) in the circuit.
    That is not nearly as easy as stepping the voltage down.

    See this data sheet:
    http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1327
    And this:
    http://pdfserv.maxim-ic.com/en/ds/MAX641-MAX643.pdf
     
  12. Energizer Alkaline AA lists 2850mAh nominal capacity at C/100, that is, at
    25mA.

    But 5V at 500mA is 2.5W; assume 70% efficiency from a boost converter
    home-made by a beginner, so the batteries need to supply about 3.6W total.
    Each battery supplies half of that power, so the draw is 1.8W/1.5V = 1.2A
    when the batteries are charged, going up to 1.8W/0.8V = 2.2A at the
    nominally-discharged point.

    From the curves at http://data.energizer.com/PDFs/E91.pdf one can see that
    drawing around 2A is much higher than the battery is rated for, and
    substantially reduces its capacity. Extrapolating from those curves I'd
    guess the actual capacity at that rate is somewhere around 500mAh, meaning
    the batteries will last about 15 minutes. Probably not enough for a charge.
     
  13. mc

    mc Guest

    I wonder if he really needs 500 mA. What will this be powering?
     
  14. jasonbot

    jasonbot Guest

    I wonder if he really needs 500 mA. What will this be powering?

    I want to power my iPod Video, USB 2.0 device, technically it should
    use 500mA, maybe not. I've seen other designs on the internet using
    2AA's powering the iPod for at least 3hours.
     
  15.  
  16. Well, there's an easy way to find out. Get some 5V power supply and a mA
    meter.

    petrus bitbyter
     
  17. jasonbot

    jasonbot Guest

    Well, there's an easy way to find out. Get some 5V power supply and a mA
    lol, First I need to MAKE a 5V power source???
     
  18. mc

    mc Guest

    Then it definitely does not consume 500 mA all the time.

    The Maxim chip that I mentioned earlier is probably the way to go. There
    are not any large differences in efficiency between different chips of that
    general type.
     
  19. Not necessarily but that's what I should do if I hadn't one already. You can
    try to borrow one or use it at a school lab. You can even buy a 5V wallwart
    or a 9-12V type and connect a 5V regulator to it. But one thing is for sure:
    If you want to make something with nothing you will end up with nothing.

    petrus bitbyter
     
  20. jasonbot

    jasonbot Guest

    The Maxim chip that I mentioned earlier is probably the way to go. There
    The maxim chip seems great but maybe a little complex, I got my ideas
    from here:
    http://www.instructables.com/id/EGBQJPLCB2EP287KTZ/#CEVEIRM4776EP288H78

    And would now like to expand on the idea, I dont want to buy the kit
    because I want to marvel at my own design, I have a basic idea but now
    need to put th eplan into action. How woul 4 AA's 6V with a regulator
    compare with the 3V step up, the 6V would be much easier.
     
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