Re: Using a PC PowerSupply as a bench power supply.

On Apr 27, 6:40 pm, w_tom <w_t...@xxxxxxx> wrote:
On Apr 26, 11:03 am, sid <sidwe...@xxxxxxxxxxx> wrote:

The article discussed minimum loads, but it I don't recall where it
stated AT or ATX.
You stated the gray (power good) wire could be ignored, but I thought
that the board needed to put a signal back on this wire to turn the PS
on for the rest of the system ?
Is this not right?

Power supply controller ordered the PSU on via the green wire.  Then
gray wire (Power OK) would tell the power supply controller that power
supply was working.  You don't care about the gray wire signal.  But
is using a power supply controller, then the controller does care
about the gray wire voltage.

  Posted were wires defined by color.  Color was defined in ATX specs;
not in AT power supply specs.  That posting assumed ATX wire colors.
And then some ATX type supplies don't use industry standard wire
colors.   If in doubt, this graphic helps identify what each wire is
by connector position:
   http://www.hardwarebook.net/connector/power/atxpower.html

  Every voltage has sense connection.  Usually sensing is performed
inside the power supply.  However, some supplies may locate the sense
connection via motherboard so as to compensate for wire voltage
losses. IOW might use one 3.3 volt supply lines, instead, as a 3.3
voltage monitoring wire.  If that sense is implemented and not
connected to other 3.3 volts (orange) wires, then the sense will
instead monitor 3.3 volts via a diode inside power supply.  This will
cause the 3.3. volts to be maybe 0.5 volts higher than what the power
supply believes it to be.  IOW if a power supply needs a sense
connection between "a brown and orange wire", then connecting all
three 3.3 volt wires together (at twenty pin connector - see chart in
previous citation) will cause the power supply to drop maybe 0.5 volts
to be closer to 3.3 volts.

 Most supplies don't use a sense wire.  Instead the sense wire is used
as another source for 3.3 volt current as shown in that chart.

  Best is to connect all same voltage wires together at the load - to
eliminate any unexpected variation - such as using one 3.3 volt wire
to monitor 3.3 voltage.

Thanks for all the input !
One last question, no where did I see the discussion of how much
current can safely be drawn from each circuit.
Is there no hard-set rules on this or just a fucntion of the size of
your PS.

Thanks


.

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