On Mon, 12 Feb 2018 09:02:19 +0000, "dennis@home"
wrote:

On 11/02/2018 23:09, Archibald Tarquin Blenkinsopp wrote:
On Sun, 11 Feb 2018 20:47:33 +0000, "dennis@home"
wrote:

On 11/02/2018 19:01, Archibald Tarquin Blenkinsopp wrote:

My last 4th generation Kindle came without, but the same item had one
included a couple of years back.

It also give toddlers something to practice on before they progress to
the 13A shuttered sockets.

If you are sure its an isolated SELV device and not some cheap
switchmode supply that may well be reference to mains?

I dont think an smps is deliberately referenced to the mains. Without
a ground reference, most SMPS provide a slight tingle, capacitive
pickup I presume.

AB


Bigclive has certainly shown some SMPS to be referenced to ground and
others with poor separation of mains and USB.

Yes! I do recollect now that you mention it, some SMPS had a high
value resistor between the 0V and ground.

At a guess I would assume that it was to stop a flashover from items
powered from the supply that might produce a charge. A CRT could
produce a few sparks from all manner of places if the aquadag wasnt
making contact with the return.

They should have isolated feedback and transformers in then but they
aren't all as good as they should be.


I would be very surprised if they were not fully isolated, they may
not be of course, but a fully wound transformer running at kHZ has so
little copper, it would hardly be worth using an autotransformer.

Mind you, I cannot find a diagram for any of the sockets, but switch
mode is the only practical solution. A 50Hz tranny would be
ginagerous and no other supply would provide isolation.

AB