On Tue, 5 Sep 2006, Harondel J. Sibble wrote:
He goes on to say on page 304 and 305, that some PSU's have
an internal load resistor and will startup without ANY load
attached, but that most modern PSU's require less load than
above, but nonetheless require a load for startup due to the
nature of switching vs. linear power supply design.
True, generally switching power supplies do need a minimal load
(whether that is supplied by an internal "load" resistor or by
an external load) to at least get the PS *started*.
------------------------------
<http://www.smpstech.com/mtblog/minimum_power_supply_load.html>
Minimum Power Supply Load
"I like the concluding sentence in the comment, "So, we say
that a minimum load is necessary to waken the power supply."
I've never heard it put this way, but it is often true."
------------------------------
And from the posted article:
------------------------------
<http://www.formfactors.org/developer%5Cspecs%5CATX12V_PSDG_2_2_public_br2.pdf>
3.4.3. No-load Operation
No damage or hazardous condition should occur with all the DC
output connectors disconnected from the load. The power supply
may latch into the shutdown state.
------------------------------
BTW that was a impressive switching PS article. Thanks
Harondel, for posting that url.
I imagine that most of this comes into play when testing a PS
outside of the computer case. Usually a PS attached to a mb
with a processor and ram should startup the PS. On the other
hand if the PS is completely disconnected from the mb (and
any/all other items), then it's very probable (if it does not
have an internal load resistor) that it will appear *dead*.
It's a good idea to attach the PS to at least a "minimal" load
to be sure it will crank up. :) The PS "under heavy load" test
is different though, and is not what this discussion is about.
Note that *NOT ALL* switching power supply designs work in this
manner and may not have the "kick-start" requirement.
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