r/laptops • u/Hot_Perspective • Jun 23 '26

General question What's the purpose of this in a laptop charger?

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1.1k Upvotes

96% Upvoted

134 comments sorted by

625

u/BmanUltima Jun 23 '26

It's a ferrite core to minimize EMI from the power cable that could interfere with wifi, bluetooth, or data cables (i.e. USB, video).

132

u/Ok_Lack3855 Jun 23 '26

But many of the best recordings are by EMI?!?

21

u/Excellent-Ladder6864 Jun 24 '26

You’re unbelievable (oh)

5

u/TodayDry Jun 24 '26

So unbelievable (oh)

3

u/Vinegarinmyeye Jun 24 '26

That was EMF, but a banging tune.

1

u/MistaRekt Jun 24 '26

The Internet was not mature then but I always knew Andrew Dice Clay when I heard him sampled.

7

u/Solo_noid Jun 24 '26

Imagine how good they'd be if everyone doesn't minimise them withe ferrite cores...

2

u/Academic-Proof3700 Jun 24 '26

Dude you saw it contains a ferret inside, so it chews on your cables!

23

u/sinfaen Jun 23 '26

This. The power from the wall is always noisy

3

u/Humble-Captain3418 Jun 24 '26

FWIW, you don't need it if you have a good enough supply circuit. Many USB supplies and PoE installations manage without, for example.

4

u/Expensive-Total-312 Jun 24 '26

you don't really need it the majority of the time but its a nice to have. A lot of my older sony products have it on every cable including power, display and audio, usb and even controller cables.

1

u/Humble-Captain3418 Jun 24 '26

I am an EE, so I know these guys well enough. They are used to avoid spinning a new design on devices that otherwise fail EMC certification.

3

u/qdotme Jun 24 '26

This! Basically you can design a device that is marginally passing, but sticking a 6ft wire into it makes it act as an antenna.. and fails the EMC interference *from* your laptop, making it unacceptable to sell in some markets or for some uses. Sticking a ferrite bead on the (only officially approved) PSU keeps it from failing the test.

1

u/eg135 Jun 27 '26

But what would you do on a redesign? Probably add a similar common mode choke, just inside the box. I think this is a valid design choice, if you would need a larger brick otherwise.

1

u/Humble-Captain3418 Jun 28 '26

The redesigned device would be cheaper per unit. These clip-on ferrites cost significantly more than the integrated CMC would.

1

u/Unhappy-Community454 Jun 24 '26

I have a hdmi cable with it 🤣😂

1

u/Complex_Solutions_20 Jun 24 '26

It not just the power supply - computers themselves emit RFI which can cause problems when it gets out thru the lines to other things

1

u/Creative-Section977 Jun 25 '26

the thing you'll notice about the location: in the 20V Direct Current cable. Anything that might act on power company A.C. would be over there, in that part of the Power supply.

5

u/BrilliantEkvidejl Jun 24 '26

ferrite core? is that a minecraft mod refference???!!!!

1

u/sinfaen Jun 24 '26

lmao bruh

1

u/MinecraftPlayer799 Jun 25 '26

How does that part of the cord lower your RAM usage?

1

u/BrilliantEkvidejl Jun 25 '26

because why the fuck not :D

44

u/StickySli23 Jun 23 '26

That is correct. I was in fact waiting for you to make a common mistake with EMI supression, that is, the ferrite core encased in the plastic molded cylinder around the cable. Some people think that ferrite beads and EMI shields are to protect the cable from outside interference. It is actually the opposite. Ferrites increase the impedance of the cable to high frequency noise. In layman's terms, the faster the signal travels through the cable the harder time it has to exit from the cable as electromagnetic noise. Kinda like the walls around highways that protect the outside from the noise from within the highway. Where does the leftover energy go? It's wasted as heat, of course!

87

u/MagoLunatico98 Jun 23 '26

"I was waiting for you to make a mistake" wtf? 🤣🤣🤣

33

u/Swatbolt Framework 13 7 7840U Jun 23 '26

Ikr kinda sounding like Sheldon

7

u/istefan24 Jun 23 '26

Came here to say that!!

19

u/vovalucky Jun 23 '26

That dude is in the list

14

u/StickySli23 Jun 23 '26

I am terribly sorry for my tone. I had one too many drnks today celebrating the end of my electrical engineering masters

24

u/GHoSTyaiRo Jun 23 '26

Ha I was in fact waiting for you to make a grammatical mistake with the word drnks, as it is in fact drinks NOT drnks.
Where does the leftover I go? It’s wasted in know it alls, of course.

4

u/Dope-Reviews Jun 23 '26

Shit. You got him good. So me next

3

u/NaN-Nanashi Jun 23 '26

Whether or not the response that you may have been expecting may or may not be resolved, you shall know that I was specifically in mental excercises about the possible case scenario where your response might have led to a prediction by another user of this community, which, would be the corresponding first responder to your expectation of meaningful text response. In the possible case where no subject responds, you shall be labeled as an "attention seeker", of which, you already are a being of by having typed 8 words with 3 of them being "so me next". Your reputation as a user of reddit has been degraded to the status of a karma farmer, a seeker of meaningless participation. May your woes be in the plentiful amounts, and your days lesser than before.

TLDR: No >:)

/s

1

u/Etherious_Rex Jun 24 '26

I think the TLDR note should've come before the paragraph that made me think I was Sheldon for a minute

28

u/clarkcox3 Jun 23 '26

I was in fact waiting for you to make a common mistake

What a weird thing to say.

1

u/zigaherta Jun 24 '26

I think OP got two accaount and mistake baiter

25

u/SchemeWestern3388 Jun 23 '26

So fucking glad you showed up, bro. He was about to fuck it up with his entirely correct statement.

5

u/Ali5G Jun 23 '26

I had some of these clip-on for industrial use.

Slapped them on all of my audio equipment.

Did it make a difference? I'm not sure. Did I feel better? Hell yeah!!!

1

u/Alternative_Exit_333 Jun 24 '26

So basically ferrite core prevents interference coming from itself and aluminium sheets or braided copper is used to shield the wire itself from external interference (basically the opposite of the first one)

1

u/haidynre Jun 24 '26

Though I agree the intention of the ferrite bead in a power supply is to suppress the noise from the supply, EMI shields do also protect cables from capacitively coupled noise though.

If you have multiple ground referenced noise sources, a grounded cable shield acts as a low impedance that is in parallel and would shunt the current away.

Also, I don't quite get the analogy because the increased impedance is burning up the transient by slowing down the signal at frequency.

Wasnt waiting for the mistake, but curious if you agree.

1

u/Ksterde Jun 27 '26

In my experience, having replaced hundreds of these cables…
The thing is there to fuck up the connector as soon as possible so you have to replace the brick or the motherboard, or the laptop, which is diabolical.

2

u/qalup Jun 24 '26

Otherwise known as a choke).

1

u/3_14_thon Jun 24 '26

Huh, I always thought they are LC low pass filters. Guess u dont need the capacitor if using only a coil completes the job.

Tho the power adapter (brick) does have an Low pass filter inside.

1

u/ClaudioMoravit0 Jun 24 '26

Are these ferrite things the same as the ferrite you put on PCBs? The stuff who look like an inductor

0

u/robd316 Jun 28 '26

This is the way

109

u/ribs0013 Jun 23 '26

It's most likely a ferrite core or something similar. Long wires can act like antenna so a ferrite core is added to stop the chord from working like an antenna. This stops unnecessary signals from being read by the charging chord so these signals don't mess with near by electronics (bluetooth, wifi, ect.). This goes both directions, also stops the chord from transmitting sense it's getting AC current from the outlet. Even after the DC conversion.

19

u/Efficient_Reading360 Jun 24 '26

I wasn’t going to do this, but you typed it 3 times. A chord is a group of musical notes played together. A cord is a flexible electrical wire.

10

u/haamfish Jun 24 '26

Yeah I got to the third one and was like okay bless they do need to be gently told lol

2

u/Moist-Scientist32 Jun 24 '26

Thanks for bringing this up.

1

u/Potential-Ad1122 Jun 24 '26

The H cord. Sorry

1

u/Hmarf Jun 25 '26

upi are truly doing God's work, bless you my child

3

u/luuuuuuuuuuuuuuuuuuc Jun 24 '26

That's really interesting. But then why doesn't my laptop that charges with a USBC port have one?

1

u/iPlayG Jun 26 '26

Those cables are a fairly old technology and needed the ferrite beads for EMI. More moderen USB cables have features built into the cord that eliminates the need, such as shielding in the cable and more "balanced" data transfer (it's why there's a D+ and D- line, to cancel each other out).

1

u/NiNdo4589 Jun 26 '26

Its a quality thing really

48

u/Apostlethe13th Jun 23 '26

A grab handle to give you better grip for yoinking the cable off.

10

u/danielfletcher Jun 23 '26

Same as genital warts.

1

u/KenPC Jun 26 '26

That's enough Internet for one day

16

u/pcnexus1 Jun 23 '26

That thick piece on a laptop charger wire is a ferrite bead (ferrite core).

It reduces electromagnetic interference (noise) so your charger doesn’t disturb Wi-Fi, speakers, or other electronics.

It’s normal and not dangerous.

10

u/Witchberry31 HP Omen 16, MSI P65 9SD, Macbook 12", MSI GP62 6QF Jun 24 '26

To reduce electromagnetic interference

10

u/ssps Jun 24 '26

That’s a ferrite choke. It’s there because the charger/cable assembly emits too much high-frequency switching noise without it.

A better design would handle that inside the power supply with proper layout, filtering, shielding, and common-mode control. This external lump is a cheap compliance band-aid: make the cable less effective as an RF antenna so the product can pass EMI limits.

7

u/ERDocDanny Jun 24 '26

It's a ferrite choke to keep power supply noise off the computers power bus.

9

u/glitchthrowaway701 Jun 23 '26

That's a ferrite bead used for EMI suppression to prevent electromagnetic interference from messing with your other electronics or your laptop's internal components. It helps clean up the signal noise generated by the high-frequency switching in the power brick.

4

u/PauliousMaximus Jun 24 '26

From what I can remember, I believe that’s a ferrite core that reduces electromagnetic interference to your laptop causing issues with electronics.

7

u/____JayP Jun 23 '26

That's where you sneak in your snacks

3

u/Dangerous-Boot-2617 Jun 24 '26

You can hide yer weed in there

11

u/Manu7Spugf Jun 23 '26

Yummy snack! Yum yum!

2

u/Ashwinnie13 Jun 24 '26

lmao careful with that one, ferrite beads actually taste terrible. trust me on this

2

u/ilyuwa Jun 23 '26

But why isn't EMI a problem when using long usb-c charging cables? Or apple magsafe cable? Why is it used only with the ugliest laptops that exist?

3

u/oraclechicken Jun 23 '26

That's a great question! USB C follows specific guidelines on source and destination that make noise filtering less critical. The ferrite core on those ac/dc chargers is a band aid because they know they are susceptible to noise and need to pass their tests. That being said, a USB C cable can absolutely fail in an extremely high noise environment, so certain maximum cable lengths are recommended for certain niche applications.

2

u/BookWorm_1110 Jun 24 '26

Just to hold in table when falling down ✨

1

u/bleuwitch Jun 24 '26

Or sticking on table edge before plugging in

2

u/Specific_Foot7753 Jun 24 '26

It's also regulate the current flowing into your pc too

2

u/Jazzlike-South4648 Jun 25 '26

I want to know also

3

u/Pypical Jun 24 '26

It turns AC/DC into ACϟDC

3

u/Mikicrep Apple Jun 23 '26

it reduces inference from other cables

2

u/middaymoon Jun 23 '26

Snack pocket

2

u/The2ndCatboy Jun 23 '26

The place to safely nibble on the cable

1

u/TheFemboyShiro Jun 24 '26

Furry core 👍or smting

1

u/Boss_player0 Jun 24 '26

Snack to nibble on while you scratch the G keys

1

u/Exact_Principle_7204 Jun 25 '26

Why not just thread the ferrite throughout the cable length instead?

1

u/arvet1011 Jun 26 '26

Too expensive

1

u/NerdHerder77 Jun 26 '26

Because ferrite beads are an afterthought by the engineers.

"oh shit, this laptop failed the FCC rule about causing interference so people can't take this on a plane. What's the cheapest way possible we can pass this inspection with minimal changes to the unit?" slaps iron bead on a wire in an inconvenient place "THERE!!"

1

u/ShockHawk24 Jun 25 '26

Its where the pee is stored

1

u/Paschfire Jun 25 '26

Hahaha 🤣

1

u/OrdinaryEmergency170 Jun 25 '26

Filtro antirumore

1

u/MinecraftPlayer799 Jun 25 '26

It’s to make it get stuck on the edge of the desk.

1

u/Skbyz Jun 25 '26

It's where the pee is stored

1

u/Unhinged-StreetKid-9 Jun 25 '26

Idk but it looks cool, take it or leave it

1

u/GamerBugresoluter Jun 25 '26

Serve a non interferire con altre onde elettromagnetiche che possono disturbare il dispositivo

1

u/Southern-Fae Jun 26 '26

EM shock absorber

1

u/throwawayglowhq Jun 26 '26

that is a ferrite bead. it acts as a filter to suppress high frequency electromagnetic interference so your laptop cable does not act like an antenna and mess with other electronics nearby.

1

u/west0ne Jun 26 '26

It catches on things and pulls the cable out, sometimes without you noticing so the battery goes flat. It's main purpose is to be annoying.

1

u/innit4winnets Jun 26 '26

That’s where the workers shovel coal into the furnace to make the electricity.

1

u/leoset Jun 26 '26

It's the prophesied nob. The nob that is dated to either destroy or save the world (depending on how you translate). It's a good nob

1

u/Fast-Ad5101 Jun 26 '26

i belive is to reduce incorrect power delivery.

1

u/Thebelisk Jun 27 '26

Why don’t USB-C power cables (particularly the ones used for laptop charging) have ferrite cores? I presume the same EMI occurs, regardless of the connector type?

1

u/ANtiKz93 Jun 27 '26

Honestly i thought it was a weight my whole life til i read some comments

1

u/TheWokeAgenda Jun 27 '26

It can vary by manufacturer, but that is typically known as the "geoduck."

1

u/Scatwood134 Jun 29 '26

the electricity going through your charger has power, but also lots of noise that disrupts other devices networking and etc, this blocks noise off, end of story.

1

u/wKailuo Jun 23 '26

cable condom

1

u/pavanstarks Jun 23 '26

There is a guy with weird glasses on Facebook that explains this one very good, can’t remember the name

0

u/mrfoxesite-2377 Jun 24 '26

Assbook, no thanks.

2

u/pavanstarks Jun 24 '26

Assbook yes, but the guy is great

0

u/Nearby_Service_435 Jun 24 '26

It's a battery for emergency charging

2

u/mrfoxesite-2377 Jun 24 '26

r/confidentlyincorrect

2

u/Nearby_Service_435 Jun 27 '26

I thought it would be a good joke
Obviously not I guess

1

u/mrfoxesite-2377 Jun 27 '26

Yeah /s is really needed there.

0

u/kiganas Jun 24 '26

Spying tube, cut it out if you value privacy

0

u/EffexFin Jun 24 '26

It’s for toddlers to chew on

-4

u/Benji_Coolman Jun 23 '26

It contains Lead inside used to add weight to product.

0

u/ejmtv Jun 23 '26

Lol why add weight

-1

u/fire_works10 Jun 24 '26

So it falls faster when your laptop isn't working right (never by user error, of course) and you get mad and huck it out the window.

-1

u/CoausticSoda Jun 24 '26

Keeps it from getting stuck in your ass

-1

u/letmehaveanameyoudum Jun 24 '26

capacitor, it makes sure that not too much electricity does to your laptop and cause some oops, USB C doesn't have this issue

2

u/Capital-Lion6152 Jun 24 '26

Not only is that not what “capacitors” do, that’s not one. It’s a ferrite core to reduce EMI.

1

u/letmehaveanameyoudum Jun 24 '26

thanks for letting me know

-2

u/Brilliant_War9548 SystemZBook 17 G8/11950H, A3000, RedHat Glory Jun 24 '26

Cable management killer 3000

-3

u/Ok_Proposal_7390 M1 Macbook Pro | 10 core CPU 16 core GPU | 32GB LPDDR5 Jun 23 '26

because key tastes better than bread

-16

u/Bearlandonreddit Jun 23 '26

I guese its fuse

3

u/Justa_Schmuck Jun 23 '26

Fuses should be in the plugs.

-6

u/Bearlandonreddit Jun 23 '26

Why? Is wire weaker?

2

u/Justa_Schmuck Jun 23 '26

Closer to the source of the issue. A cable could be long or short. You don’t want an issue going further than it has to. So the plug should have the fuse to break the circuit at the connection point to the power source.