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12V to 24V dc (Voltage Doubler)

Discussion in 'Electronic Design' started by Sean J, Apr 5, 2004.

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  1. Sean J

    Sean J Guest

    If any one can help, I've run into another problem, Roland sent me this
    circuit (it works fine), but it runs the battery flat quite quickly

    http://www.aaroncake.net/circuits/6-12conv.htm

    " I have a 12V dc car battery and I need to run some truck electronic
    equipment, approx. 24V / 25mA "

    I wonder if anyone can help me with a schematic of a Voltage doubler from
    12V dc to 24V dc. I have seen one in a Electronic mag a long time ago. It
    used 2 transistors which oscillated, and 1N4007, a cap, etc. I only need
    25mA at 24V dc at the output. Please if anyone can help, I would greatly
    appreciate it, thanks.

    Sean
     
  2. scada

    scada Guest

    Search for a DC to DC converter. www.jameco.com has several. Ex: Part#
    155694CF is: 9-18V input, 24VDC @ 625ma output for $35. These off the shelf
    units also sport nice features such as filering, I/O isolation, continuos
    short circuit protection, etc...
     

  3. That seems good advice in general. However, the OP is concerned about
    battery drain, and a converter capable of 625mA is probably going to be
    rather inefficient at only 25mA (what the OP requested).

    Jameco does not seem to have many 24VDC output converters. But since the
    output is isolated from the input, another option would seem to be to use a
    12V converter and put the output in series with the input, like this:

    .--------------------------------.
    | |
    | .-----------------------. |
    | | | |
    12V in --o---|in+ +out|----|----- 24V out
    | 12V isolated | |
    | DC-DC converter | |
    GND-----o---|in- -out|----'
    | | |
    | '-----------------------'
    |
    '--------------------------------------- GND

    Jameco has an 84mA 12V DC-DC converter, part 216830CA, for only $10. The
    only downsides I can think of to doing it this way are that the output
    voltage is only as regulated as the input is, and that any noise generated
    on the input side by the converter will also show up on the output. But
    those problems would be true of the circuit he envisions, as well.
     
  4. scada

    scada Guest

    I'm not sure I agree that the 625ma converter would be inefficiant at the
    25ma load, but I can see your concern. Jameco #161701CF is a dual output
    +12V -12V unit. The datasheet shows separate output lines, I don't see a
    reason that they could not be put in series! It's rated for 125ma (each
    output) 3W - for only $21.
     
  5. Spajky

    Spajky Guest

    http://w1.859.telia.com/~u85920178/power/vconv_01.htm

    -- Regards, SPAJKY ®
    & visit my site @ http://www.spajky.vze.com
    "Tualatin OC-ed / BX-Slot1 / inaudible setup!"
    E-mail AntiSpam: remove ##
     
  6. Bill Bowden

    Bill Bowden Guest

    You might do it with a 555 timer and couple caps and diodes
    but you won't get the full 24 volts. Look at the circuit
    "Generating -5 volts from 9 volt battery" at:

    http://ourworld.compuserve.com/homepages/Bill_Bowden/page10.htm#5volts.gif

    Leave out the zener diode and it will produce about -10.5 from
    a 12 volt battery so there will be about 22.5 volts from the negative
    output to the + side of the battery.

    I don't know it it will deliver 25mA or not, it's rated at 12mA.
    Maybe try larger capacitors.

    -Bill
     
  7. The basic issue is that quiescent current starts becoming an issue;
    higher-powered converters tend to draw higher quiescent current.
    That would probably work, too. Do you know of a good reason to spend the
    extra $11 over the solution I suggested?

    -w
     
  8. MNQ

    MNQ Guest

    Why not use intersils ICL7660sipa. this ic will convert your 12 volts
    to -12 volts. You should be able to use this as a 24v supply but current
    supply may be limited to about 10ma you will have to check the data sheet.
    It also seems to be efficient. Checkout the data sheet.

    Naveed
     
  9. R.Legg

    R.Legg Guest

    What is the battery current drain?

    Is Q3 getting warm? This is supposed to be a darlington. If you're
    using something else, it may be running linearly.

    There are some things you can do to cut down on consumption, or to
    make a non-darlington work correctly.

    1) Increase R1 through R4 by a factor of 2. If Q3 is really a
    darlington, R5 and R6 can be increased similarly.

    2) Decrease C1 and C2 by a factor of 10 to .01uF.

    3) Keep the inductor larger than 470uH. 1mH is a good ballpark figure
    at this low power level.

    4) Disconnect the collector of Q4 from the base of Q3 and reconnect it
    to the base of Q1.

    These all tend to keep Q3 from operating linearly during a switching
    interval, at a reasonably high operating frequency, for the power
    level expected.

    Turn the circuit on and off at the 12V battery, not at the 24V
    terminal.

    To reduce overshoot at turn-on, due to mvb early operation, stick a
    feedforward network across the zener string. 10K and .01 should do it.

    Stick a snubber across D2 - 2N2/220R if it interferes with the radio.
    If you can get a faster part for this position, please use it.

    This is a pretty flakey circuit, but can be made to function and uses
    no parts that are hard to find or to substitute.

    RL
     
  10. scada

    scada Guest

    As you stated in your first email:
    "The only downsides I can think of to doing it this way are that the output
    voltage is only as regulated as the input is..."

    The 161701CF has an input range of 9-18 VDC giving better regulation and
    being dual output provides complete isolation!
     
  11. Ah, but neither of those seems to be important to the OP (judging by the
    circuit he was looking for). So I still think mine is the best solution to
    the problem as posed :)
     
  12. N. Thornton

    N. Thornton Guest

    If you lack tronic knowledge, you can set a relay self oscillating by
    wiring it so the coil is on, but when the relay closes the coil is cut
    off.

    Now, direct your 12v via 2 contacts to 2 different large capacitors,
    put the caps in series... 24v.

    Very crude but works.

    Regards, NT
     
  13. Roger Gt

    Roger Gt Guest

    X-No-Archive: yes
    "N. Thornton" wrote
    : "Sean J" wrote
    : > If any one can help, I've run into another problem, Roland
    sent me this
    : > circuit (it works fine), but it runs the battery flat quite
    quickly
    : > http://www.aaroncake.net/circuits/6-12conv.htm
    : > " I have a 12V dc car battery and I need to run some truck
    electronic
    : > equipment, approx. 24V / 25mA "
    : >
    : > I wonder if anyone can help me with a schematic of a Voltage
    doubler from
    : > 12V dc to 24V dc. I have seen one in a Electronic mag a long
    time ago. It
    : > used 2 transistors which oscillated, and 1N4007, a cap, etc. I
    only need
    : > 25mA at 24V dc at the output. Please if anyone can help, I
    would greatly
    : > appreciate it, thanks.
    : >
    : > Sean
    :
    : If you lack tronic knowledge, you can set a relay self
    oscillating by
    : wiring it so the coil is on, but when the relay closes the coil
    is cut
    : off.
    : Now, direct your 12v via 2 contacts to 2 different large
    capacitors,
    : put the caps in series... 24v.
    : Very crude but works.
    : Regards, NT

    Okay, this is a "Vibrator converter" Relays are not really rated
    for this application. IT WILL WORK, but switching Capacitors is a
    pretty rigorous requirement and the relay will likely fail after a
    few months. Put it on a socket and use one with a 5 Ampere rating
    for this application. (You can draw about 500ma max with a 10
    times rating on the contacts.) Caps should be at least 470mFd to
    1KmFd.

    Also it is Noisy. Vibrators in Car radios were loud enough you
    could tell if the radio was on from the vibration of the dash
    board!
     
  14. That would hardly meet the OP's stated goal of improved efficiency :)
     
  15. N. Thornton

    N. Thornton Guest

    After rereading the q I guess youre right. A 1w coil relay running 50%
    duty cycle = 0.5w, at 12v thats about 40mA.

    Regards, NT
     
  16. Rich Grise

    Rich Grise Guest

    For 25 mA, why not just 12V worth of lithium batteries?

    Cheers!
    Rich
     
  17. Saad Ahmed

    Saad Ahmed Guest


    One simple solution would be to use a single chip switched cap voltage
    converter made by linear (www.linear.com) using an LTC1144 (just type
    that in to the search) There is a voltage doubler circuit in the
    datasheet. You would need a couple of caps and some diodes.

    Hope it hepls

    Saad
     
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