Alf,
it's not correct to compare a SMPS with this topic. All SMPS are isolated.
Output terminals are behinde a transformer for sure!
Why is it then not correct to compare them? In directly line-powered
power amplifiers, the output terminals are ALSO behind a transformer -
this being the RF output transformer!
And regarding all SMPS being isolated, well, better say "many" instead
of "all". Because some are definitely not isolated. Many SMPS are
intended to power some device that really doesn't need to be insulated
from the line, and then the designer of the power supply saves cost by
not using a transformer. For example, the "electronic ballasts" used
with all sorts of fluorescent lamps are basically non-isolated SMPSs.
Most SMPSs for powering motors are also non-isolated - see my web site
for an example, fully described with schematic, PCB, etc. And many older
CRT-type TVs used non-isolated switching supplies.
Manfred
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