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12v to 6v converter/regulator

Discussion in 'Electronic Basics' started by dreed75, Jul 26, 2005.

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  1. dreed75

    dreed75 Guest

    I have looked all over for a chip or a schematic that allows me t
    convert 12v to 6v and I can't find anything. I can find 12v to 5
    with no problem at all but I need 6v. Would a simple voltage divide
    work? The load changes so I don't think a voltage divider will wor
    but I am not sure. The current will be up to 3A at some times but a
    low as 500mA at other times. Thanks

    Davi
     
  2. Michael

    Michael Guest

    Look at the LM317 regulator with a pass transistor.

    The 317 will do up to 1.5 amps (with heatsink).

    Just make sure the input voltage is at least a couple of volts higher than
    the desired output.
     
  3. The LM2587 is an adjustable, up to 5 amp switching regulator chip.
    http://www.national.com/pf/LM/LM2587.html#datasheet
     
  4. mike

    mike Guest

    Do you mean 12V like 12.00VDC?
    Or do you mean 12V like plug it into a car?
    If it's the latter, you have a LOT more things to worry about.
    mike

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  5. ehsjr

    ehsjr Guest

    The LM317, LM350 and LM338 and two resistors will all do that.
    The chips (on heat sinks) can handle up to 1.5 amps, 3 amps
    and 6 amps, respectively.

    The LM317 with a PNP pass transistor and a few resistors is
    probably your best choice. Simpler, but more costly, would be
    the LM250 or LM338. Here's the circuit with the pass xsistor:
    PNP
    2N2955
    e c
    +12 -----+------ ---------------------+
    | \ / |
    3[R1] ----- |
    | | ------------ |
    +--------+------|in LM317 out|---+--- Vout +6
    | ref | |
    ------------ [R2]240
    | |
    +----------+
    |
    [R3] 910
    |
    Gnd

    There will be a voltage drop across R1 (3 ohms) as the LM317
    provides current to the load. The more current that is
    drawn, the greater the voltage. The effect is to cause the
    transistor to conduct when the current drawn is about 200 mA,
    and the more current that is drawn, the harder the transistor
    conducts. R2 (240 ohms) and R3 (910 ohms) form a voltage
    divider that "programs" the LM317 to produce very close to
    6 volts. If you need it to be precisely 6.00 volts, substitute
    a 10 turn, 1000 ohm pot for R3 and adjust it to the exact voltage.

    Consult the datasheet for the LM117/LM317 for more detail.
    http://www.national.com/ds/LM/LM340.pdf

    Ed
     
  6. Mochuelo

    Mochuelo Guest

    On Tue, 26 Jul 2005 03:35:21 -0500,
    Unless you want and know how to dissipate appropriately 18 W, you must
    go for a switching converter. Forget about linear regulators.
     
  7. rayjking

    rayjking Guest

    Hi,

    You may not want to do this but by using two IR2110'S and 4 fets and a
    toroid with two wires bifilar wound . Connected as you would a push pull,
    center tapped 6 to 12 volt converter and replace the two diodes with two
    fets. This must be driven with a 40 to 50 % on each half cycle. You now have
    a synchronous rectified voltage doubler that is bi-directional and if a 12v
    charger is applied to the 12 volt output you will also charge the 6 volt
    battery.

    I have built such a device for a friend to add a 12v battery to a triumph
    motorcycle because the 6v batteries are no longer made. The 6v charger
    charges the 12v battery and the electrical system is all 6v. Above I used
    the 555 timer and 4013 to divide by two and give a symmetrical output.

    Ray
     
  8. quietguy

    quietguy Guest

    You could do a little experimenting with a mobile phone car charger -
    just change the output voltage divider resisters and bobs your auntie

    David - who finds the local tips are full (big exaggeration, but..) of
    them
     
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