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power supply circuit

Discussion in 'Electrical Engineering' started by F Murtz, Jun 9, 2008.

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  1. F Murtz

    F Murtz Guest

    I would like to make an adjustable power supply using a transformer with
    a 24v 5a single wound secondary I would like the voltage to be
    adjustable from lowest to highest possible given transformer I would
    like to have regulated current

    There is another possibility I also have a larger transformer with two
    32v 4.7a secondaries If anyone has a schematic for an adjustable power
    supply with adjustable current regulation making the most of the
    transformer specs I would be eternally grateful
  2. James Sweet

    James Sweet Guest

    There was just such a power supply published in Radio Electronics in the
    early 90s, I'll have to see if I can dig it out and scan the article.
  3. I did a Yahoo Search on 24V REGULATED POWER SUPPLY, and got several hits,
    the first one is

    and it has a 350mA version of what you asked for. Surely you can research
    the hit list for more of your requirements, but I found most of your stuff
    in less than a minute.
  4. Palindrome

    Palindrome Guest

    Whilst you might get lucky and find a variable supply design based on a
    24v 5a transformer(or one with 2x 32v 4.7A ones) - the odds are that you
    won't. The best you might find is one based on a 24v 4a one, or a 20v 5a
    one - 24v 5a is just too unusual a starting point for a variable supply

    However, what you will find is loads of designs of *regulators* based on
    a range of dc input voltage.

    You need to make a critical decision: "linear" or "switch mode"
    regulator. Your transformer can (roughly) produce 100W.

    With a linear design set to give a high current, low voltage, output -
    that 100W will be dumped into the power supply - which means big heat
    sinks, fans, low efficiency, etc. So there is extra complexity in
    getting rid of this excess heat.

    With a switch mode design, there can be problems with stability when
    running on very low outputs.

    For both, there can be problems giving outputs set below a couple of volts.

    My suggestion would be to go for the following building blocks:

    1) A standard full wave rectifier unregulated first stage - this design
    is well documented.

    2) A limited range switch-mode regulator with manual output setting

    3) A full range linear final output regulator with manual output setting.

    Stage (2) can be omitted initially - it is only there to increase the
    efficiency overall and reduce the heat dump problem. It can be added
    later and then modified to automatically adjust itself.

    The LM117 may be a bit old, but is an excellent starting point. The
    application notes actually give you the circuits for both (2) and (3)
    that you need, complete with all the values for the components: Regulator/LM117.pdf

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