[Amps] Direct rectification of AC mains to drive the amp,

[Manfred Mornhinweg]

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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