🚀 go-pugleaf

On Tue, 10 Mar 2009 18:18:04 -0800, Robert Baer <robertbaer@localnet.com>
wrote:

>Sylvia Else wrote:
>
>> Sylvia Else wrote:
>> 
>>> I've recently bought a D-Link DIR-300 wireless router. While 
>>> disconnecting its power supply from it, I got a tingling sensation 
>>> when I touched the plug (to be clear, I'm talking about the 5V DC 
>>> plug, not the mains plug).
>>>
>>> An AVO meter shows about 90V AC to earth from either side of the 5V 
>>> plug. Short circuit current to earth is about 0.1mA.
>>>
>>> Still, I thought these things were meant to be completely isolated. 
>>> Has there been a change of approach?
>>>
>>> Sylvia.
>> 
>> 
>> Apparently it's normal, and is related to RFI suppression.
>> 
>> Sylvia.
>   RFI? Think not; that voltage is about half the line, and is from 
>capacitave coupling from primary to secondary (if transformer type).


  Line filters both keep noise OUT of your device, and keep noise that
your device makes from getting out.  Mainly of the EMI type.

  A quote from wiki:

     A line filter may be used to attenuate EMI in either direction. For
example:
           Emissions: It may be used to reduce the unintentional
conducted emission from the equipment, to a level sufficiently low to
pass regulatory limits (such as FCC part 15). For example, in switching
power supplies.

           Immunity: It may be used to reduce the level of EMI entering
the equipment, to a level sufficiently low not to cause any undesired
behavior. For example, in equipment used in Radio Transmitter facilities.

  As soon as she said RFI I laughed, and then the donkey agreed.  I
busted a gut!