F Murtz wrote:
> 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
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
design.
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 do***ented.
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:
http://www.dee.hcmut.edu.vn/vn/bomon/bmdientu/tailieu/datasheet/Voltgage%20Regulator/LM117.pdf
Enjoy!
--
Sue
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