Regarding a load on the 5V supply. Is this really necessary on the
current ATX power supplies. Isn't there a current standard that states
this should be handled inside the PSU? If this is so, then jumpering
the green and black will be all that is really necessary for a current
ATX PSU to run.
Why do you think that? I've never seen anything about this.
I have seen surplus switching supplies that include load resistors, but
they have nothing to do with the common computer power supply.
Think about it, the one line that will most definitely get loaded is
the one that also just happens to supply the most current, the +5v line.
Undoubtedly the supplies are designed so the load of a motherboard (and
maybe some minor peripheral) is enough so the supply can run. There
is no need for a built in load resistor because the supplies are intended
for a specific appplication, that will be enough of a load.
If they put a load resistor in the supply, it makes it easy for you when
you are using the supply for something other than a computer, but it's
just unwanted heat in the power supply for the use that the power supplies
are designed for. They need those high current supplies because the
computer needs it, so why waste it with a load resistor?
Another way of looking at it comes up every time someone wants to
use a computer switching supply as a general purpose bench supply.
They go through the rigamarole of adding a suitable load so the
switching supply runs, and then use the supply to power something
that barely needs any current. Far better to just throw together
a linear power supply out of scrap that is just intended for the
needed lower current, than waste current with a load resistor in
order to get the switching supply to do something it wasn't intended
for.
Michael
