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reduce 6vdc to 4.5vdc

Discussion in 'Electronic Basics' started by Ken, Oct 8, 2004.

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  1. Ken

    Ken Guest

    Hi all,

    Been doing some research through the archives and have seen where I'm
    probably going to be using a regulartor, however, does anybody have any
    truly simple circuit diagrams for this type of thing?

    Trying to reduce a car charger from 6v DC to 4.5v DC for to use as a PDA
    charger.

    Thanks,
    Ken
     
  2. Lord Garth

    Lord Garth Guest


    Ken, you might open it up and look for the info on the chip. Often, the
    output
    can be changed simply but it depends upon the design.
     
  3. If you can get to not oscillate, a low drop out adjustable regulator
    should work. I have often had to use a 1 uf film cap in series with a
    1 ohm resistor output to ground to do this. Perhaps an LM2931CT.

    http://cache.national.com/ds/LM/LM2931.pdf
     
  4. anonymous

    anonymous Guest

    Im prob wrong but I thought that cars put out 12V DC. You're probably
    referring to a device that plugs into a car lighter socket? Ah.
     
  5. anonymous

    anonymous Guest

    Trying to reduce a car charger from 6v DC to 4.5v DC for to use as a PDA
    (cut myself off)

    how much current would you need?

    If you could get more than 6 V from the car you could drive a voltage
    regulator like a 7809 and then use a voltage divider to get the resultant
    4.5.
     
  6. Ban

    Ban Guest

    The cheapest would be to put 2 diodes 1N4001...7 in series between the power
    supply and your PDA, they reduce the voltage by 1.3...1.5V depending on the
    current and temperature.
     
  7. Rob Paisley

    Rob Paisley Guest


    Question.

    What sort of "car charger" are you talking about; A charger for a 6
    volt lead-acid automobile battery or one for a NiCad battery from a
    radio controlled toy car?

    Rob.
     
  8. Ken

    Ken Guest

    Hi all,

    Thanks for all the replies.

    The car charger is a cigarette lighter charger for a magnavox cd player that
    puts out 6v DC. My pda takes 4.5~5v DC.

    My EXTREMELY limited knowledge of component level work is why I'm looking
    for some "simplistic" methods of making this happen.

    Thanks,
    Ken
     
  9. Ken

    Ken Guest

    Thanks, I'll give this a whirl. Going to check and see if Radio Shack
    sells them.

    Thanks again,
    Ken
     
  10. Clarence

    Clarence Guest


    Without knowing what the circuit is in the charger you may be in for a nasty
    surprise. If the unit is current regulated with a voltage clamp at 6 Volts,
    with all the schemes using diodes as the battery is charged the output of the
    charger will tend to rise to 6 volts. As the current through the diode drops
    this voltage WILL BE APPLIED to the battery. The over voltage MAY have reduce
    battery life, or battery heating. (Heat will also reduce life, but getting hot
    has other problems for the battery, like overcharge.) BE VERY CAREFUL and
    test the circuit carefully.
     
  11. Jamie

    Jamie Guest

    you want to be careful with that, most likely you have more than 6 volts
    from the charger on the Peaks.
    any ways to make it simply for you, use lets say 3 diodes silicone
    2 or more amp diodes in series with the cathode(line side) heading to
    the PDA and the anode(non line side) coming from the + side of the
    charger..! also one should have like a 12 volt car auto tail light
    incandescent lamp in series as a current sink.
    i know its kind of back yard electronics but i think it's more of what
    you understand and can handle.

    [charger + out]-->>--[incandescent lamp]--[-diode >| ]--[ diode ->|
    ]-->> PDA + input.
     
  12. Lord Garth

    Lord Garth Guest


    Silicone? New technology I suppose...
     
  13. Ken

    Ken Guest

    Hi all,

    Here's a macro photo of the board and I've added the numbers from the sides
    of the (caps; at least I'm guessing they're caps).

    http://www.helpconsulting.net/images/cigarettecharger.jpg

    Thanks for all the help! I went to RS and picked up a couple of IN4005's
    and put them in series on the unit and the voltage still read 5v on the
    digital multimeter.

    Regards,
    Ken
     
  14. Ken

    Ken Guest

    update! The diodes are working correctly at this point.

    I tested them with a meter and they were still reading 5v, however, after
    speaking with my brother who is an electronic (board leve) technician, he
    stated that there needed to be some type of draw on the system, thus once I
    actually plugged in the PDA it started charging properly instead of the
    safety kicking in and shutting down the system.

    Thanks all!!

    Ken
     
  15. Rich Grise

    Rich Grise Guest

    Go to Radio Shack and get a 4.5 volt lighter adapter. :)

    It sounds simplistic, but your existing "charger" is probably not designed
    to act like an ordinary DC supply - it might have some kind of charging
    algorithm built in. A proper adapter is less than ten bucks.

    Cheers!
    Rich
     
  16. Rich Grise

    Rich Grise Guest

    He's plugging it into the lighter socket. Just a 317 at 4.5V, running
    right off the car's 12V should work, but a RS 4.5V lighter adapter
    would be cheaper and WAY less PITA.

    Cheers!
    Rich
     
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