Is there a simple way to make a computer power supply variable and maintain
high current? I keep seeing designs that use LM317T's, but they're limited
to 1.5 A or less. I'd like to be able to retain as much of the current as
possible but keep it simple. Thoughts?

Thanks in advance,
Jake

On Oct 10, 8:36*am, "Jake Omega" wrote:
Is there a simple way to make a computer power supply variable and maintain
high current? *I keep seeing designs that use LM317T's, but they're limited
to 1.5 A or less. *I'd like to be able to retain as much of the current as
possible but keep it simple. *Thoughts?

By design, a computer power supply delivers high current at low
voltages
(5V and 3.3V), which are unlikely to be useful for anything BUT a
computer.
If you want a general-purpose power supply for experimentation,
a 40V range and settable current limit are important qualities
that the 'computer power supply' lacks.

A 'simple' power supply is a string of batteries. A flexible one,
with
knobs and meters, is easily built or purchased, but not simple.

Jake Omega wrote:
Is there a simple way to make a computer power supply variable and
maintain high current? I keep seeing designs that use LM317T's, but
they're limited to 1.5 A or less. I'd like to be able to retain as
much of the current as possible but keep it simple. Thoughts?

Thanks in advance,
Jake


Jake,
PC power supplies are switchmode designs, designed for fixed output voltages
needed by computer components. This means that the PSUs are designed to
operate within very tight tolerances, limiting the adjustability to quite a
small range.
You would have to change the basic design of the SMPS control circuitry so
that it could provide power over a wider range of voltages. Changing basic
design of the supply also means changing or modifying a few major components
in the PSU.
Take a look at the page at http://www.pavouk.org/hw/en_atxps.html to get an
idea of the inside of a PC power supply.
Also, look at the following web sites to see how a PC PSU can be modified to
provide 13.8VDC at high current.
http://thedatastream.4hv.org/at_psu_hack.htm
http://www.webx.dk/oz2cpu/radios/psu-pc1.htm

Bear in mind that these mods are still fixed voltage output, not variable.
My suggestion, if you really need a high current variable bench supply, is
to figure out what you actually need, in terms of voltage ancd current, and
buy or build from scratch, a PSU that will fill your needs. Linear supplies
are much easier to build than SMPS power supplies, especially variable
voltage/high current units. Read a lot about the Astron series of linear
supplies at http://www.repeater-builder.com/astr...ron-index.html.
Get the data sheets and application notes on some of the more popular
3-terminal linear regulators and see how to make them give higher output
current.
http://www.repeater-builder.com/astr...-regulator.pdf
http://www.repeater-builder.com/astr...m117-lm317.pdf
http://www.repeater-builder.com/astr...regulators.pdf

--
David
masondg44 at comcast dot net