[aprssig] Emergency Power for Ham stuff

Robert Bruninga bruninga at usna.edu
Fri Jan 22 12:47:42 CST 2016


>> But every AC/DC switcher is just a DC/DC supply with a rectifier in
>> front of it....

> Bob, you should know better than to use the word "every".

That modifier applied to the the complete noun of the sentence: "AC/DC
switcher..."  the key word being "switcher".  I am not aware of any
switching powersupply anywhere that does its DC/DC switching directly from
60 Hz AC alternating current.

> There are plenty of cheap power supplies out there that will not fit your
> "every"

I agree.  But they are not switchers...

>  I've had plenty of switching supplies that were most certainly not
> isolated.

I agree also.  I was only saying of the 5 sealed laptop switching power
supplies that I tested, all of them were isolated.  I agree, most open frame
and modern supplies are not isolated.  But many of the consumer sealed
"laptop" type supplies are.

Bob, Wb4APR

-------- rest of original message -------

It only takes looking at many schematics out there to see that it's not
always an isolated design.  You have to have a transformer (and not just the
flyback of the switcher which frequently is not configured as an isolated
transformer, you need a full galvanic isolation transformer) to have an
isolated supply.  If you have just a diode front end going to the oscillator
there's no isolation.  Google the schematics, you'll see them.

You are also describing a "come as you are" approach and many people are not
going to have quality power supplies, they're going to have
rock-bottom-cheap power supplies that could prove dangerous.  Many laptop
supplies are also ultrasonically welded shut so there's no way to easily and
safely open them to inspect the circuit (of course many of the
come-as-you-are people may not know what to even look for if they opened
it).

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