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Are wall warts better for EMC?

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cupoftea

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Hi
Wall warts have no mains cable back to the socket...this cable could act as a noise antenna.
Is this why people prefer wall warts to eg laptop style power supplies which are kind of midway along the overall supply cable? (between mains socket and product)
 

Wall warts have no mains cable back to the socket...this cable could act as a noise antenna.
Is this why people prefer wall warts to eg laptop style power supplies which are kind of midway along the overall supply cable? (between mains socket and product)
I think the main reason for the difference is that laptop supplies are generally to large to directly plug into the wall.
Doubt that EMI is a consideration, since the power supply pretty well blocks any EMI from the device being powered.
 
The big thing is, sending DC to the "appliance" may eliminate
internal switching supplies altogether for a big win (and any
EMC for the wall wart, is somebody else's journey and already
sorted (UL certs too, with your client being now low voltage DC
and maybe off the hook for that too).

Corded external supply, same deal - you buy "good to go"
for regulatory compliance.
 
Hi,

The wall socket isn't the "source of power" ... it's still supplied by cables inside the wall. I don't see why a power cord outside the wall should act as antenna, while the cables inside the wall should not act as antenna. Makes no sense for me.

Klaus
 
I think when you get it EMC approval tested, the "cable in the wall", is assumed to be in a shielded metal conduit? The bit from the socket , woudl not be.
 

I think when you get it EMC approval tested, the "cable in the wall", is assumed to be in a shielded metal conduit? The bit from the socket , woudl not be.
Is it so? Which EMC test specification are you referring to? Conducted or radiated test?
 
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