On many of the power cords for my high-tech equipment, there is a plastic bulge a few inches from the computer end of the power cord. Sometimes, this same bulge can be found on USB and other peripheral cables. It is not the transformer, as that is larger and usually at the wall end of the cord (and wouldn’t be on a USB cord at all). It doesn’t appear to be some sort of strain-relief mechanism, like the strain disconnect on XBox controllers.
So, what are these for?
Thanks, y’all.
oh boy…
That is a core which forms a “parallel” choke, which de-couples common mode signals on the cable (like rf etc) and only allows “push pull” currents.
It’s an “RF choke”.
Details? It’s a lump of ferrite. The wires in the power cord are looped around the ferrite; and it blocks radio-frequency (RF) interference from exiting the equipment and traveling down the cord into the power lines and causing interference and noise in other appliances connected to the power line, such as your boombox.
There are often similar lumps on headphone adapters and audio cords; my camcorder has an audio output cable with one.
Sometimes, the RF choke will be built into the equipment, either in the connector (very common), or on the circuit board.
IANAEE
Could it be a ferrite coil to help stop electronic noise? It’s my understanding a power cord could be its own antenna without it, and noise entering or leaving an electronic device is never a good thing.
My fear is that someone will actually answer these, because I probably won’t understand the answers, but:
How does an arbitrary electronic device (a PC, say) cause RF signals on its power cord?
How does wrapping the wire around a ferrite core block RF noise?
Detailed details: it’s a ferrite toroid, a short tubular hunk of ferrite with the cord running through its center. Ferrite is a category of grey, hard, brittle ceramics made by sintering together various metal oxides. Its reason for being is that it has a very high magnetic permeability and low electrical conductivity, especially in the high KHz or the MHz frequency range. Magnetic fields will prefer to form inside this toroid encircling the cord, rather than in the air around the cord where they will radiate outward and mess with your other electronics.
You may have noticed AM radios sometimes have an antenna that looks like fine wire wrapped around a dark cylinder. That cylinder is a rod made of ferrite.
Obligatory wiki. Apparently, the technical term for it is a “ferrite bead.”
A PC generates huge amounts of RF energy as a byproduct of the squarewave nature of digital signals transitioning from logic ons to logic offs billions of times per second. It’s just pure “hash” and is unwelcome at any hapless radio that happens to be near.
To contain this interference, PCs are built in metal cases, or plastic cases with metal linings. But, that’s not enough - the RF signals can also escape on the cables plugged into the PC, so ferrite cores are placed on the cables to attenuate (reduce) the RF. As **Napier ** said, the ferrite core is a more “attractive” place for the RF energy to go to, as opposed to travelling outward in the air or along a wire, so the ferrite effectively kills a lot of the RF before it has a chance to get very far.
Almost everything electronic today must pass a battery of EMI emission & susceptibility tests. The “ferrite around the power cord” trick is a cheap way to help improve the performance of the device when it comes to EMI emission & susceptibility.
Those damn arts and crafts people get their little hands into everything!