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how can i decrease voltage.. help me plz

Discussion in 'General Electronics Discussion' started by javed, Sep 11, 2010.

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  1. javed

    javed

    4
    0
    Sep 11, 2010
    how r u...
    i am new user ...
    Sir
    i am making a charger battery which is showing 7.11Volts but Nokia Mobile needs 5V.. what should i do now .. kindly help me ..thanks you very much
     
  2. LTX71CM

    LTX71CM

    182
    0
    May 23, 2010
    For future reference it's preferred and polite to start your own thread when it's not something directly related to the current topic.

    To answer your question you'll want a voltage regulator such as the common 7805. Google it for tons more info.
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    Is this open circuit or under load. If it's an open circuit voltage, try placing a small load on the charger (say 1k) and see if the voltage drops to 5V. It may be that there is insufficient load to allow the regulator to work.

    On the other hand I may be completely misunderstanding what you mean. An alternative reading is that you want to charge a Nokia phone from a battery that measures 7.1 volts.
     
  4. javed

    javed

    4
    0
    Sep 11, 2010
    sorry sir
    i have cordless battery of Panasonic which shows 3.5 volts and 1500 ampairs i want to charge my nokia mobile..what should i do... kindly help me...
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    Do you mean it is marked as 1500 mAh and measures 3.5 volts when charged?

    Is it NiMH, NiCad, or LiPo, etc...

    Do you actually have 2 of these, or was your originally quoted 7.1 V some sort of error?

    If it's less than 5V you will need a SMPS in boost configuration (which is not trivial) and it is likely that there is insufficient power in a single pack to fully charge an iPhone.

    If it is > 5V you have other options -- possibly a simple linear regulator (although quite likely a low-dropout one)
     
  6. javed

    javed

    4
    0
    Sep 11, 2010
    yes sir u r right
    i have just 3.5 Volt battery with 1500 mAh and i want to charge mobile with it.. what should i do to charge mobile. which thing i should attach with this battery...
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    Do you have 2 of them? If you do then you can connect them in series to get 7V and then use a low drop-out regulator to regulate that to 5V.

    With one battery you would need a boost switch mode regulator, but it's a poor option as a single battery (even assuming 100% efficiency) won't have enough capacity to fully charge your iPhone.
     
  8. javed

    javed

    4
    0
    Sep 11, 2010
    ok Thank you very much i am trying ...
     
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