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Safe supply voltage for cell phone

Discussion in 'Electronic Repair' started by Ignoramus15609, Apr 9, 2007.

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  1. I have a Motorola V550 cell phone. When I use it as a modem, it drains
    its battery quickly. So, I decided to make an auxiliary power supply
    for it, to be used when I am away from AC power.

    The phone's AC adaptor supplies 5.81 volts when the phone is not
    plugged in, and 5.61v when the phone is charging. The phone starts
    charging when supply voltage reaches about 4.8-4.9 volts.

    I bought a battery pack that has about 6.7 volts when fully charged.

    I would like to know if, in your opinion, it can be simply connected
    to the cell phone directly. Or is 6.7 too much.

    If, in your opinion, 6.7 volts is too much, an easy option to consider
    is to just add a diode like N4007 for a 0.7 volt voltage drop.

    Any thoughts will be appreciated etc.

  2. James Sweet

    James Sweet Guest

    I'd put a diode in series just to be safe. It'll probably be fine either
    way but you can't really tell without looking at the circuit design.

  3. I'm not sure if the .9 or so volts would be to much but you might not want
    to risk it since theres no reason to. You can use a diode but make sure you
    get one that can handle the current(look at the AC adapator and see how much
    its rated for). Ofcourse if you use a diode you'll be wasting that power
    but if you don't mind then its no big deal(not like its that much anyways).

    Since your using it as a modem you might want to tap into your computers
    supply. It should have a 5.x(not sure bout a laptop but I would imagine it
    must have one) voltage that you can use. Should be ok as long as the cell
    phone doesn't use to much current and would probably be worth the effort
    instead of having to have to seperate supplies and waste the batteries.
  4. Guest

    then you want 4.something volts
    too much by about 2v
    Get the right battery, trying to drop it may damage the phone. Diode
    drop depends on current, its not 0.7v IRL except at i~=0.

  5. I thought that the ideal voltage would be 5.61 volts.
    Thanks. Some people recommended some low dropout regulators that could
    be helpful for me.

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