Now, lets take a second round on this issue...

I think it's clear that I need a isolation transformer.
It also looks like it would be best to connect the IT
between the mains and the device under test, not to the
scope, right ?

I have checked a few electronics catalogs, and the IT
seems to be from $150 USD and up starting with aprox 300VA
units.

Now, my device under test is realy low power. It's a
"transformerless power supply" with a "secondary" voltage
of 5V. Maybe 5-10 mA in average on the 5V rail. Just a 400V
"X2" cap, a few resistors, a low voltage smothing-cap, a zener
and a 78L05. I does work, a get 5V as messured with a battery
powered voltmeter, but I'd like to "see" what what the 5V
rail "looks like" under load.

So, would it be possible to put together something
inexpensive either with some ready made (smaller)
transformar, or buy handwinding something ?
Any design tips ?

Jan-Erik.



llile@SALTONUSA.COM wrote:
>No Isolation Trasformer = BOOM! or Yeeoooooow!
>Isolation transformer = OK
>Hook the isolation transformer to your device under test, not your scope.
>If you hook the isolation transformer to your scope, the scope ground will
>become live when you hook it to your circuit.

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