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Output 4 to 22 volts.

Discussion in 'Electronic Repair' started by micky, Mar 16, 2013.

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  1. micky

    micky Guest

    I've gotten used to the idea that power bricks and other things can
    accept 110 to 240 input volts and still put out the same output
    voltage. Xener diodes, iirc, and all that.

    But lately I've been seeing wall warts and power supplies that not
    only have variable input, they say they have variable OUTPUT. I saw
    a little wallwart at Best Buy, for 10 or 15 dollars that said this,
    (4.5 or 6 volts to 12 volts**) , and now I notice that my Targus
    car/plane laptop power supply (which I've never actually used, except
    one 3 minute test) says it puts out 4 to 22 volts DC.

    How does it know which to do? When? And how does it do it?

    How does the wallwart keep from overcharging with 12 volts a device
    that needs only 6 volts?


    Ths also relates to my question in the next thread, which I hope to
    post later tonight.
  2. Variable-output power supplies have been around for many years.

    The voltage is selected with a switch -- the supply doesn't "know" what
    voltage is needed.

    I've never seen one with continuously variable output.
  3. Phil Allison

    Phil Allison Guest

    ** Such unit are SMPS = Switch Mode Power Supplies.

    ** It doesn't know.

    YOU have to know and set the adjustments appropriately.

    Makes them a real hazard to use.

    ** SMPS are not battery chargers.

    ..... Phil
  4. How does the wall wart keep from overcharging
    ** SMPS are not battery chargers.

    They are if the device is charged from its AC adapter.

    I have a number of SMPS chargers, for cell phones, juke boxes, camera
    batteries, etc.
  5. Phil Allison

    Phil Allison Guest

    "William Sommerwanker = TROLL "

    ** A * Power Supply * is not a battery charger.

    ** No.

    You have a number of SM battery chargers.


    .... Phil
  6. Jamie

    Jamie Guest

    But, there is no supervisor circuitry in them, the power supply, which
    is what you have only supplies the raw power needed for both the device
    and the charging circuit inside the device.

    You and I may get some flake over that one :)

  7. A battery charger is a specialized type of power supply. It is intended to
    deliver "power" to rechargeable batteries.
  8. Phil Allison

    Phil Allison Guest

    "William Sommerwanker"

    ** Massive red herring and straw man fallacy.

    Plus a blatant context shift.

    Wot a desperate wanker.
  9. Guest

    I have several universal ones here from Kensington. They made them in
    70 watt and 115 watt versions. The 115 watt one has input cords for
    120VAC, 12VDC (car lighter adaper), and a rather funky round one for
    (I believe 24VDC) airplane supply. The output cable has a 5 pin
    connector and there are a number of output adapters. A little
    experimenting showed the output adapter sets the output voltage and
    current limiting. Opening one up revealed three resistors, used to
    set those parameters.

    There are a couple of ways a supply can avoid sending an overvoltage
    to a device. A fuse in the output and hoping the device has diode
    protection would be one. While it would be possible to manufacture a
    supply which ramps the voltage up until it hits a reasonable current
    draw, it isn't very practical.

  10. micky

    micky Guest

    Here's the wall wart: adapter&cp=3&lp=2

    Dynex - Universal AC/DC Power Adapter dx-ac501
    "Converts 120V AC to 3-12V DC
    With 500mA maximum output.
    For 3V, 4.5V, 6V, 7.5V, 9V and 12V power."

    The picture only shows 3 sides of the thing, I'll open the box next
    time I'm at BestBuy, to see if there are any switchers on the other 3
    sides. .

    For the laptop adapter, I looked some more and found
    It turns out there are interchangeable tips that each connect to the
    power supply, and in each tip is a resistor. The wire from the PSU
    has 3 wires and a shield in it, and if one connects the grey wire to
    the yellow or the shield via a resistor, the value of the resistor and
    whether one ues the yellow or the shield determines the output

    So you're right. It's told what voltage to make, although not so much
    by a switch but by a resistor value in the tip.

    Thanks for the help.
    Well, I don't know that it's really continuous. The text above
    suggests that the wall wart can have 6 different outputs. And the
    laptop power supply can have 30 different voltages, though I'm sure
    not every one has a tip that yields it.
  11. micky

    micky Guest

    No, I guess not. I am used to replaceable tips, but didn't expect
    the tip to control the voltage.
    At least with the laptop power supply, I have to use the right tip.
    Well, it seems Targus got around that, in this universal power supply,
    which is no longer made. I forget what they make now, and I don't
    know how other manufacturers set the voltage.
    Well, they do charge the battery of the laptop.
  12. Phil Allison

    Phil Allison Guest

    ** There is a charge regulator inside the laptop - fuckwit.

    Wot a tool.

    ..... Phil
  13. micky

    micky Guest

    That doesn't change anything. Kerplunk.
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