On 06/10/2017 08:20, Jeff Layman wrote:
Somewhat OT to your question, but what is the RFI like from these
unswitchable USB power supplies? There's an interesting video here
showing the interference from a cheap and nasty power supply compared to
a branded one. OK, it's not USB but the principle is the same. What I
found interesting was that there was a fair amount of RFI even when the
rubbish SMPS was unloaded. That's somewhat similar to the situation with
these built-in mains-socket USB power supplies.
A number of years ago, my PC was using a CRT display, which worked OK
but took a lot of room. Idly flicking through the local paper one day I
noticed a PC for sale, working and complete with keyboard, mouse and TFT
monitor The asking price was less than half the price of the cheapest
TFT monitor on the market at the time, so I answered the ad and bought
it having had it demonstrated as working. The seller thought it was
taking up too much room and had invested in a laptop, so he was getting
rid of the desktop tower and accessories.
Back home, I swapped my CRT monitor on my PC for the TFT monitor from
the newly acquired machine and it worked perfectly. I then tried the
CRT monitor on the newly acquired machine, and with a tweak of the
refresh rate that gave me a second usable computer, except that there
was nowhere to put it permanently within cable reach of the router and
it had no wireless capability. So I invested in a Through The Mains
ethernet connection pair and put it in an upstairs room, and then set up
a file sharing capability and arranged an automatic back-up of my normal
PC onto the spare PC's disc. So far so good.
Nearly a year later I had my arm twisted to give a presentation to a
social group, and realised very quickly that it would not be practical
to use a desktop but I had to have something capable of connecting to
the social club projector, so I bought a refurbished cheap Toshiba Tecra
from a company that specialised in recycling old computers. It came
with a power supply "for Toshiba" rather than the native Toshiba unit,
and the first time I plugged it into the mains and switched it on the
Through The Mains ethernet connection lost carrier. The fake Toshiba
power supply powered the Toshiba laptop OK, but threw so much
interference into the mains that the house mains wiring became incapable
of passing data. I eventually bought an extra long ethernet cable which
I ran up the stairs to replace the Through The Mains units.
As for the original question, I looked up the specification details for
the unit available from Screwfix.
3.1A total output, shared across 2 outlets
USB charger stand-by power made when not in use
2 x Type A, 5V USB sockets
With smart USB connectivity
Standby mode when device is fully charged
Auto detects USB device & adjusts charging pattern to suit
So it looks like it goes into quiescent mode, but the USB facility is
completely independent of the on/off switches for the mains sockets.