On Sun, 30 Dec 2012 18:58:46 +0000, Lee <
cyber...@ukonline.net>
wrote:
Not really. ;-)
The practice of using analogue regulators inside economic SoHo
switches to stabilise the "nominal 6/9 voltage" feed from a typical
wall wart has long since passed into ancient history (along with the
external dial up modems associated with such technology).
What has been used, out of sheer necessity[1], during the preceding
decade or so is switching supply technology. This turns out to have
the rather beneficial effect of allowing almost any wallwart of a
sufficiently minimum power output[2] to be used as long as the output
voltage remains in the region of 5 to 16 volts (and, in a lot of
cases, right up to 25 volts - just check the voltage rating of the
input filter capacitor used by the switching regulator inside the
ethernet switch itself to be absolutely sure on this point).
[1] Initially, there was little to choose between the ancient and the
modern technologies on component costs. However, a modern switching
regulator could readily achieve conversion efficiencies in excess of
85% vastly reducing the waste heat compared to an analogue solution
which could quite easily be producing more waste heat than that of the
ethernet switching circuitry itself (especially true when a cheap
chinese unregulated wallwart was chosen as the primary power source).
Even when it cost more than an analogue regulator, the use of a
switching one could allow even cheaper and nastier wall warts to be
used and a smaller amount of metal or plastic for the case allowing
even greater reductions in manufacturing costs.
A typical 5 or 8 port SoHo Gbit ethernet switch only sucks around 4
to 6 watts from its wallwart supply (although the voltage / current
requirements marked on the switch itself will indicate a higher figure
than this to guarantee a suitable margin for error in the rating of
the wallwart supply - typically marked up as twice what the gadget
actually consumes).
As long as the VA rating (for DC this is wattage) of your chosen
replacement wall wart equals or exceeds the 'rating plate' figure of
the ethernet switch, its output voltage can be anywhere from 6 to 16
volts (and possibly right up to 25v if you've confirmed the voltage
rating of the input capacitor in the switch's psu circuit).
This can even work on switches that come supplied with an ac output
wall wart. This last possibility will only apply on kit that has the
fullwave rectifier bridge and smoothing capacitor relocated from the
wallwart to the psu circuitry within the case of the switch (usually
to permit a larger VA rated transformer to be used without making the
wall wart excessively bulky). In this case, a smaller more efficient
smpsu wall wart can be used as a replacement to the original ac output
wall wart[3] which can save the 2 or 3 watts typically dissipated by
the wall wart transformer itself[4].
[3] This is an exercise that I've successfully done about a decade
back with an 8 port fast ethernet switch.
[4] These days, most such chinese made transformer ac only output
wall warts typically waste 2 or 3 watts just by virtue of being
plugged into the wall socket alone. Long gone are the days when the
likes of the GPO / BT carefully specified the quality of such
transformers which typically only wasted quarter of a watt on no load.
--
Regards, J B Good