I have a torroid filter on the end of my laptop's power supply cord right by where it enters the laptop. I know that this is for filtering RF, but is it there to keep supply noise out of the laptop or laptop noise out of the supply (and general vicinity)?
I am guessing it is to keep noise out of the laptop, hence it's position right by the laptop, but maybe there is more to it than my limited sense of logic dictates.
What say you?
Jon
Jon Danniken wrote: ===================
** Neiter. Such toroids are for EMI suppression.A bit of RF noise will not affect a computer but will of course get into the front ends of a radio or TV set.
..... Phil
I probably helps pass FCC or CE radiated EMI limits.
-- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
Correct
Typically the toroid reduced radiated emission from the device in the 100MHz range
-- Klaus Kragelund
Thanks Phil. I am re-purposing a laptop power brick for another device because the voltage and ampere ratings are in line with what I need. I don't know if the surgery adapting it to a GX12-2 connector will permit me to keep the toroid on the end of the cable, so I am glad to know I can safely have the option of removing it.
Jon
Thanks John, I appreciate it.
Jon
If you remove it, it is not compliant any more. The manufacturer did not add it for fun ;-)
If it is at the laptop end of the cable, then it is likely to have been needed to make the *laptop* pass EMC testing (by preventing the long cable from acting as a transmitting antenna for the laptop), and so the power supply may well have been compliant without the laptop. (If the ferrite core had instead been placed at the power supply end of the cable then I would suspect that the power supply was the noisy bit.)
I have an Epson scanner which has such a huge ferrite core on the cable of its power supply that it is only slightly smaller in size and weight than the rest of the power supply. It has made feel a bit sorry for whoever it was that had a very bad day at the EMC lab.
It is mainly to stop the RF noise escaping from the laptop. The PSU lead would act like an aerial without the choke on it to block the RF.
Hence the position of the choke. The PSU should be relatively quiet although some bricks are much worse than others. Nasty cheap Chinese ones that skimp on the filtering components and sometimes also the proper electrical isolation - fit only to be used on US mains.
I can only use a Wifi dongle on my own fast laptop in combination with a USB extender cable. The local interference field near the case probably from adjacent USB sockets is enough to jam mobile phone signals.
-- Regards, Martin Brown
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