On Monday 06 January 2014 14:04 John Rumm wrote in uk.d-i-y:

On 06/01/2014 09:31, Tim Watts wrote:
On Monday 06 January 2014 09:24 Scott M wrote in uk.d-i-y:

There is only one caveat to this. SMPSs generally use opto-isolators to
provide the feedback from the LV side to the HV frequency generator
side. This and the transformer means they are totally isolated from the
mains. However, some of the very cheap ones skip the opto-isolators[1]
and use FETs or TRIACs or something[2] instead which ruins the mains
isolation, especially should they break down.

That's the bit that worries me - I would not like to have any PSU with
any sort of electrical coupling between the ELV and LV(mains) side, bar
perhaps an earth connection (that's rare now, but used to be not unheard
of to bond to earth to the -ve rail in ye olden days).

http://www.electricstuff.co.uk/acadapter.html

Fascinating - wonder how many fires those things start...

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