Macbook charger teardown: Complexity inside Apple's power adapter (2015) | Hacker News Reader

Macbook charger teardown: Complexity inside Apple's power adapter (2015)

righto.com

146 pointsblowski98 comments

The price list at the bottom [1] isn't fair, a company like Apple usually pays more for it's components for "higher" quality (usually a probabilistic reduction in failure rate). Things are so bad in the industry that it's not possible to get some of the higher rated components because Apple has bought them all.

[1] List (from reference 19 on the site):

    Component                                          Cost
    MSP430F2003 processor                              $0.45
    MC33368D PFC chip                                  $0.50
    L6599 controller chip                              $1.62
    LT1460 3.3V reference                              $1.46
    TSM103/A reference                                 $0.16
    2x P11NM60AFP 11A 600V MOSFET                      $2.00
    3x Vishay optocoupler                              $0.48
    2x 630V 0.47uF film capacitor                      $0.88
    4x 25V 680uF electrolytic capacitor                $0.12
    420V 82uF electrolytic capacitor                   $0.93
    polypropylene X2 capacitor                         $0.17
    3x toroidal inductor                               $0.75
    4A 600V diode bridge                               $0.40
    2x dual common-cathode schottky rectifier 60V, 15A $0.80
    20NC603 power MOSFET                               $1.57
    transformer                                        $1.50?
    PFC inductor                                       $1.50?

On a side note... I've seen the case where Apple's standards for compliance are set using the components they buy the highest grade of - making it even more difficult for external companies to implement compliance. It was bad enough that the standard chip, recommended circuit and recommended testing tools failed to meet their requirements.

NOTE: Apologies to any users where the screen is stretched.

The only parts on that list that would have different grades are the capacitors. It isn't a measure of quality, but the temperature and stability specs of the dielectrics.

EDIT: Source: I'm an electrical engineer and design electronics for a living and have even worked with ex-Apple engineers.

I know some processors (mostly of higher end processors) do but I don't know if specifically that processor does. I do know that at least some manufacturers will offer automotive and aerospace grade parts if requested (if not for the extra money).

There's also the fact that it's off the shelf completely because there are none left to buy because somebody else already has them. If I remember rightly it can have something to do with the component failure rate on a silicon slate.

I've also heard of stories where processors that have a co-processor by design fail for some reason and are sold for their larger processor capability only. I've seen this with an ARM chip.

There isn't a single mass market microprocessor (whether it is AMD, Intel, Qualcomm, NVIDIA, etc.) that is manufactured to be sold as a single SKU (product line like an i7-6950X). That would be economically impossible because they are complex pieces of technology where a single tiny scratch or missed dopant, errors that number in the thousands or more per wafer, can ruin a major piece of functionality. Microprocessors are designed with special "fuses" so that when there is an error, the failed part of the chip is disabled and the part is downgraded (for example, from an i7 product to an i5 product). They also go through burn in tests to test the stability of the part at various voltages and temperatures and that's how they separate automotive from regular parts (or chips meant to be sold as overclocked 2400 MHz DDR3 from regular 1600 MHz ones is another example).

You are right that is deliberately done but wrong about how often. This is literally how modern mass manufacturing of complex silicon parts works and the only companies that don't do this make extremely specialized and expensive processors like IBM does for mainframes, supercomputing, and RAD hardened applications. Those chips can be several times bigger than your tiny ARM or Intel microprocessor for the same reason.

I didn't know how common that was. Its definitely interesting, I was speaking from personal experience with these packages.

I remember being offered chips with lower failure rates too, I can't remember the ratios but it was certainly worth considering. We ended up testing the different boards off the line before doing a larger assembly (and further testing of course) because of the component failure rates. If it wasn't the solder it was the chip itself - causing really hard to find bugs I might add. I remember having two boards off the same line together, one chip could do an operation and other couldn't. This bad chip was being used for software production too...

Same goes for high precision resistors, capacitors etc. for hifi equipment. They don't have a special machine producing extra accurate components, they just take the produced resistors, test them, and bin them into accuracy classes. The high precision ones are those that happen to be very close to spec.

This is extremely interesting. Do you have any further reading to learn more?

Unfortunately, while I could point you to great books on electrical engineering in general, I don't know of a single online/book resource on this topic because I learned all of this on the job while apprenticing and contracting for many different companies. For further reading, I would probably start with semiconductor and electronics manufacturing/supply chain books of which there are dozens. If they don't cover the nuances of dealing with part variations then they are likely not worth reading. Sorry I can't be more helpful.

That's okay, thank you for sharing your knowledge. I'll take a look into the books you recommended.

I think one of the first 'mass market' processors that used this technique was the Intel 486SX, back in the early 1990s. It was simply a 486DX which had the fuses connecting the FPU blown. I believe binning by clock-speed has been used for a lot longer; the 486 33MHz parts being the same as 66MHz but having failed some sort of QA, which meant that overclocking could be attempted at fairly low risk, as long as attention was paid to cooling and you didn't mind the risk of the CPU failing completely earlier than expected.

EDIT: There certainly seems to be different quality levels for this particular processor anyway [1], which I'm sure they'll want a premium for higher quality. Feel free to correct me though.

[1] http://www.ti.com/product/MSP430F2013/quality

Which one is "higher quality?" Those are different lots with the same MTBF?

Those are various combinations of IC package, temperature grade, and bulk packaging. They are demonstrating that all the different types they sell have gone through environmental testing. There is no such thing as 'higher quality', generally, but a part with extended temperature range or a faster speed grade does cost more.

I think perhaps my wording was misplaced, but a part that has been shown to reach high temperatures might be more preferable in a charging application - even if they blow up anyway.

> The price list at the bottom [1] isn't fair, a company like Apple usually pays more for it's components for "higher" quality (usually a probabilistic reduction in failure rate).

99% of the time the difference between "quality"/automotive/aerospace parts and regular parts is literally just extra quality control steps at the input, intermediary, and output stages. The parts that don't pass Apple's muster are sold to other manufacturers so often times vendors will break even on supplying Apple just to keep their baseline business afloat while they make money on the parts that Apple won't use but others will. Based on my conversations with Apple engineers, they are especially brutal at the negotiating table because they know that they can single handedly take up all of the vendors capacity while getting at-cost parts and allowing them to profit via side channels (parts that they would otherwise discard). That may sound unfair but as long as you can keep up with Apple's standards, that means your business is set for life and you can make all the money you want with other clients who need those same parts but aren't as discerning. That's why you can't buy many of the higher graded parts: they're the same parts but Apple has first pick because Apple will always be a bigger client than you with far more negotiating power.

Chances are you could drop this price list by 25-50%, even for the custom parts, and you'd be closer to what Apple pays.

I'll add to that: I've bought some knock off iPhone cables and a MacBook Pro power supply ($84 times two for a dog chewing through it twice) and they all look similar to the real product except there's a defect

In the iPhone cable it only worked one way -- flipping it over it did not work at all. For the MacBook power supply the MagSafe connector had two slightly indented pins where one had a black circle around it.

I think these were legit Apple parts that failed QA. Who knows.

And I've given up buying them as I don't need the risk. The dog could have essily been electrocuted when chewing through a cheap wire. Also iPhone cables have gotten cheaper.

Some of the more expensive items are missing from here. Perhaps they are not commodity items.

* Irregular shaped PCB with large amount of copper on it.

* housing and heat sinks.

* special ground pin.

An amazing amount of thought went into the design of these power bricks. Now... What does that say about their choice of fray-prone insulation?

Obviously they are aware of those of us who have to buy new power bricks regularly because the insulation has shredded. (I have to buy a new one about once a year.) In some proportion, we are either 1. a profit opportunity or 2. collateral damage of an engineering decision to favor that thin insulation for flexibility or whatever.

I'd love to know their analysis!

My pattern is that I buy a MacBook, use it for a few years, resell it and get a new one.

I'm at my 5th or 6th MacBook in over 10 years, and I've always sold the laptops back with their original charger.

I have a 2011 MacBook Air that I take everywhere with me - the battery is at over a few thousand cycles (and lasts about 40 minutes) last time I checked. The charger for this one is dirty and chipped, but not frayed.

I've seen frayed cables, so I know it's a real problem, but given my experience I can't help but wonder... what are people doing with their chargers?

This! This!

I used to lose chargers frequently, when I was in college, but I didn't take good care of them. Knowing how I treated them then (Stuff in bag, and even if I wound it, it was without the slack you're supposed to give the cord coming off the brick) it doesn't surprise me that I destroyed so many.

Now, I've had the same charger for three years without issue. I suppose part of that lifespan improvements is I really have two of them -- one for my desk that never moves, and one that's always secured in my bag and well-wound.

I wonder if I had just one and moved around with it all the time if things would be different.

It could be good fortune but I've been on Macbooks since around 2003 and have had substantially better luck with power adapters since MagSafe came out. I had a few pre-MagSafe adapters fail but the only post-MagSafe adapter I've had break was a knockoff.

I recently (early this year?) had to replace the cable on the charger from my 2006 MacBook Pro (one of the black ones). I've got other chargers from the 2009 MacBook Pro, the 2010 one, I had a 2013 one for almost two years, and I've got a 2015 MacBook Air - all of which have perfectly fine charging cables.

I've never used the ears to wrap up the cable, I tend to just loop it up and stuff it in my bag if I'm taking the charger with me. I also have mostly had enough chargers around compatible with several in-use MacBooks that I'd leave a charger at work and another on the couch and another in the workshop, and rarely move the chargers around anyway. So I;m probably treating them as nicely as possible (purely by accident rather than from any desire to not damage them - I am, and Steve would have said "holding it right"...)

I do realise there is a systemic problem though - once I'd fixed my old old one, a bunch of friends can out of the woodwork asking me to repair theirs as well.

> given my experience I can't help but wonder... what are people doing with their chargers?

Forcefully bending their cables when winding them around the charger, or tensioning the cable under the little plastic bracket. Also, there are actually several manufacturers of the various generations of Apple chargers, with subtle differences in the materials used.

Don't use the little fold-out ears. The winding around them puts too much stress on the wire. Get a piece of self-adhering Velcro and use that to keep the wire together.

I'm not particularly careful with my devices yet I never had something break in the last decade - however, 2 out of about 6 Macbook power adapters have had their cable messed up and needed replacing, without any obvious reason. Ironically, the more abused power adapters (i.e. mostly taking to work everyday) fared better and are like new (except dirtier).

They completely unwrap and re-wrap the cord.

The design is defective, and cannot handle the typical stresses that it is subjected to.

Yes. "Blame the user" is not an acceptable approach to resolving a problem with even a slight incidence rate. "We don't see that behavior often enough to commit resources to addressing it" is valid, but "they're touching it wrong" isn't when you're making a mass-produced consumer-grade product, especially a product that's meant to be carried to and fro (Apple had to learn this with the iPhone 4 too).

Some people may take pride in carrying their chargers around on special hand pillows to ensure that they are kept pristine over the years, but I personally want my products to work without demanding special accommodation for themselves. I went through 3 chargers in the 4 years I used a MacBook Pro. I didn't mistreat the stuff, I just didn't pamper it.

The answer in this case is pretty obvious, though; Apple knows that an $85 power cable isn't going to cost them any meaningful quantity of customers, and actually the breakage tends to net them $85 extra per year, so they kind of like it. There is no incentive for them to un-plan the planned obsolescence of the charger.

The ridiculous thing about it is the power supply itself is almost an engineering feat unto itself.

In my personal experience, I've owned hundreds or thousands of electrical devices, but to date I've only gotten an electrical shock from my old MacBook Pro's power brick, which was an amazing device in every other way.

It speaks to the hubris of their design org.

I've never, in 10+ years of MacBooks, had to replace an adapter due to fraying. I suspect it's because I don't yank the cable out (instead grabbing the plug), but more importantly, because I don't use the cable wraps included. Just a quick over-under coil, tossed in the bag, and I'm good to go. I still use the adapter that came with my 2006 MacBook, having added one of the plug converters for the Retina laptops.

> what are people doing with their chargers?

In my case, the problem is that I use my laptop on my lap.

Even if you're careful, there's no avoiding the occasional bend. The cable can't handle this over time and breaks next to the magsafe connector.

I understand that Apple considers my use case outside of the tolerances they designed for. Nevertheless, other laptops I've used do not have such failure-prone cables.

My girlfriend showed me this: https://www.youtube.com/watch?v=VCIo8xGTUX0 a little pen spring to reinforce the cable need the connecter. I do it too, not sure if it's useful though.

Frayed cables are the result of normal use coupled with bad design. Other manufacturers have been making robust cables for decades. (e.g. http://imgur.com/a/kQt77)

You appear to be the exception.

I've been through atleast 4 laptops, and 3 tablets. Owned various Mp3 players starting with one of the original Creative Nomads. At this point countless phones as well. When I was younger I'd travel with most of console video games and of course the actual handheld ones with their chargers.

I've never had a single cord fray nor had the need to replace a charger that I didn't lose for any device except every single Apple device. With my MBPr I knew how awful the iPad and iPod cords were so I was careful to not wrap it too tight around the little feet. Both feet broke but still worked after a month. The cord still started fray on one end after about 3 months and one foot completely broke off. I still try to wrap it loosely but there doesn't seem to be much point as the amount of electrical tape I need keeps increasing on both ends whenever I replace it.

I don't think they intentionally designed them poorly, but I do think they are refusing to fix a widely known problem to bilk user out of more cash yearly. I now only buy third party iOS device cords and I wish there was a viable third party alternative for my MBPr brick.

The problem with Apple's cords is that the rubber insulation seems to be too long for the wire beneath. Both my iPhone 6 and MacBook Pro cords have their rubber peeling away from the wire. It's not fraying, it's peeling because the rubber is pushing itself away from the wire from too much tension.

Luckily, at least with the newer cords, the wire is very sturdy. The coating seems to be more for cosmetics than insulation these days. The technology inside may be impressive, but the overall quality of the product still screams "made in China". The only real explanation after many years of the same shoddy cords is that it is intentional on Apple's part, to get people buying new cords at $100 a pop every couple of years.

I agree. I have a spare charger from my wife's now unused 2006 MBP that still works and looks fine. Using it with a MagSafe 2 adapter. Ten years and no fraying, though it is dirty.

The problem is Apple put 'wings' on their charger so people wrap the cable extra-tight around them like this http://imgur.com/a/VZHoD when they should really be using the only safe method for rolling cables: Over/Under coiling (I just learned this name!) https://en.wikipedia.org/wiki/Over/under_cable_coiling

What are people doing with their chargers? My first one failed because I kept pulling at the cord instead of the head. My next ~5-6 chargers have been great.

Guaranteed they're wrapping them like hell without first giving an inch or so of straight cable out of the side of the brick.

Just peut some tape where it wears off... It works like a charm!

Or, use shrink tubing.

I just repaired my Ipad 2 frayed cord. I cut some shrink tubing I had laying around. I cut 1/2" shrink tubing length wise, and glued the ends together with Super Glue. Then shrink the tubing with heat.

It works better than I though it would.

Nice! What color shrink tubing do you use?

I use Snow white Sugru molded against the case and around the cable for about an inch. At a DevOps conference I got a freebie package in Red, later I bought a package of 6 Snow White which looks better. Keep your spares in the fridge as they dry up even in the package or give them away to friends and tell them not to store it beyond the "use by date".

Yeah, but you shouldn't HAVE to put tape there. They should make a not deficient product that can hold up to normal wear and tear.

Apparently Apple changed the make-up of the rubbery/plastic insulation of their cables to cut some toxins from the manufacturing process:

> Both are still used by other companies in power cords and headphone cables. We have replaced PVC and phthalates with thermoplastic elastomers.

http://www.apple.com/ca/environment/safer-materials/

Right at the bottom in small print it says:

> * Every Apple product is free of PVC and phthalates with the exception of power cords in India and South Korea, where we continue to seek government approval for our PVC and phthalates replacement.

Anyone from India or South Korea care to comment on whether there's a noticeable difference between the quality of the cables on the power cords vs an Apple headphone lead or something?

> A powerful microprocessor in your charger? > One unexpected component is a tiny circuit board with a microcontroller, which can be seen above. This 16-bit processor constantly monitors the charger's voltage and current. It enables the output when the charger is connected to a Macbook, disables the output when the charger is disconnected, and shuts the charger off if there is a problem. This processor is a Texas Instruments MSP430 microcontroller, roughly as powerful as the processor inside the original Macintosh.

I'm not surprised at all. Microcontrollers are ubiquitous. There's little reason to use something like a 555 timer anymore. I wouldn't have been surprised if this had been a 32-bit ARM MCU (or a 8-bit PIC).

Yeah, it wouldn't surprise me if this is fairly common, especially when you consider what happens when a lipo battery has a 'problem'. I'd want whatever's charging that up to be as exacting as possible.

All the charging circuitry resides in the laptop itself, the AC adapter is just a power supply. The reason why there is all this complexity is the MagSafe connector that makes it physically trivial to short the power pins together, which given the power levels involved might very well be plausible fire hazard.

On one project I was on, we used a 16-bit MCU for a power controller. Cost less than twenty cents, and we got a lot of functionality out of it (you can cram a bunch of complex logic into 2K of code).

Near the end of that project, the hardware engineers came to us and apologized; they had managed to source a part for the same price with twice the code space. Could have used that, would have saved quite a bit of space optimization effort.

Should have had your supply chain people push the vendor/distributor on price of the half code space part to make all of that cramming NRE worth it. ;-)

The linked video of how bridge rectifier works is enlightening, funny and terrifying. Makes me glad I'm a software developer and not an electrical engineer so I'm in no danger of killing myself if I miscalculate.

https://www.youtube.com/watch?v=sI5Ftm1-jik&feature=youtu.be

ElectroBOOM's videos are all like that. It's a comedy channel.

His videos are extremely entertaining, but his disregard for safety exaggerates the danger a little bit. My understanding is that most bridge rectifiers are put in a circuit after a step-down transformer, so they're operating on a much lower AC input voltage.

Also, don't wrap the safety ground pin on test equipment with kapton tape. Just don't.

They can be, and they are in certain linear PSUs. Linear PSUs generally make ripply DC with linear power transformer -> rectifier and then use active linear analog circuits to get clean DC power. Has very low efficiency but exceedingly low noise.

For most consumer things, you use a classic switch mode power supply design. You bridge rectify mains directly, and you switch that really fast to get the DC you need, and you filter it a lot.

Amazing that so much thought goes inside the adapter, but they still manage to completely skip any worthwhile stress relief on the cable ends. One of the reasons I know how to solder wire is because I got tired of buying a new adapter every year.

Previous discussion: https://news.ycombinator.com/item?id=10628212

> One problem with simple chargers is they only draw power during a small part of the AC cycle.[5] If too many devices do this, it causes problems for the power company.

What kind of problem?

See https://en.wikipedia.org/wiki/Power_factor#Importance_of_pow...

I think this is referencing what is known as "power factor":

https://en.wikipedia.org/wiki/Power_factor#Importance_of_pow...

I'm mostly familiar with this from UPSes, but I assume it's basically the same problem on a different scale.

Lets say you have a device that requires 110 Watts - 1 Amp at 110 Volts. And you have a UPS that is rated to provide exactly the same.

In an ideal world (spherical cows, etc), and a device with a power factor of 1 (e.g., perfect), this works.

But if you have "non-sinusoidal current" (as his footnotes word it), your device isn't actually pulling 1 Amp. If you graph the voltage and current draw out, you should see the current draw forms a wave that matches the voltage (in shape, not value). If it doesn't, then at some parts of the wave, you're drawing more current than you claim - and at others, you're drawing less. So you're still drawing 1 Amp on average, but at any given instant, you're probably not.

So back to our spherical cow UPS. What looks like a perfect match on paper, goes wrong - 60 times a second, you're drawing more than those 110 Watts and causing an overload condition. And it's an issue that gets horrible when you scale it, because every device is receiving exactly the same wave form - so every device is using more than you think at precisely the same time. Like the trope of people jumping on a bridge at the same time, each consumer causes the same condition in perfect unison with each other.

It's not really that your device draws more than the claimed wattage, it's how the power arrives.

Resistance is proportional to current (I = V/R) so drawing 100W at 240v will result in a lower resistance than 100W at 110v. In an ideal world this doesn't matter but the real world had wires with resistance etc.

This means if you draw your peak current at peak voltage you're using as little current as possible, but if the peak current is offset you'll be drawing more amps than you would if you were in phase.

This causes parasitic losses in the distribution network and makes utilities grumpy, amongst other things.

I think what you're describing is phase shift (typically seen with inductive loads), where the current sine is the right form, but lags behind the voltage sine.

The (fifth) footnote in the article has "The difficulty comes from the nonlinear diode bridge, which charges the input capacitor only at peaks of the AC signal." And "If you're familiar with power factors due to phase shift, this is totally different. The problem is the non-sinusoidal current, not a phase shift."

So the demand looks like inrush current - but inrush at every single cycle. This produces a non-constant load, where the current draw instead graphs more like an ECG and less like a sine wave. If you overlay this ECG-style graph over a perfect sine, you see that to average the same draw, the spike has to peak much higher than the sine - because it's drawing nothing for the rest of the cycle.

The net result is basically the same (which is why both problems come under 'power factor') - you're drawing current in a very inefficient manner - but that's why I'm describing 'drawing more than the claimed wattage', because at the peak of each cycle, you do.

The simple answer is that all the current (and thus all the power) is drawn at the peaks of the sin wave. This means for most of the sin wave no current is being drawn. This is a problem because now the average power rating that a power plant can produce -- where the power is produced for all parts of the wave in roughly equal amounts -- is no longer enough, they have to be able to generate much more power just for the peak of cycle.

This load imbalance is a large problem.

The term "load inbalance" is most commonly used in three phase systems where ideally the currents on all three phase/outer/hot conductors should add to zero, having no current on the neutral conductor. Having significantly different loading on the three phases will create changes in voltages on the individual conductors and generally not make efficient use of transmission capacity.

Interestingly, having a lot of switching power supplies with poor power factor correction on a three phase network (e.g. in an office building) will also create currents on the neutral, but with three times the network frequency (and harmonics), as during one cycle, the current for the peaks caused by...

  +L1 -L3 +L2 -L1 +L3 -L2

...will be returned.

I've owned couple of Macbook and Macbook pros since 2009 and never had any issue with the fraying, but I've seen one case of fraying from a friend's Macbook Pro just few months ago. I didn't think she'd abused her adapter in anyway. On a side note, I had every single original iPhone charging cable fray after less than couple of years of use (including 30pin and lightning cables from iPhone 3, 3G, iPhone 4, and my current iPhone 6). It is very annoying.

A good way to fix is to use Suguru (https://sugru.com/how-to/fix-a-broken-cable), which seems to be made to fix things like this, and stronger than heat-shrink tubing.

Title would be less ambiguous if it said Macbook Pro charger, since they have laptop called Macbook and it uses a different charger.

Are other laptop chargers similarly complex? Dell, HP, Microsoft etc

Once your power supply is capable of delivering >=75W, european norm 61000-3-2 requires you to implement power factor correction (PFC), which makes complexity balloon.

All name-brand laptop chargers will usually have it.

> requires you to implement power factor correction (PFC), which makes complexity balloon

Depends on how much is required and what your size limits are. Apple used active PFC here to minimize the size of the brick. An ATX desktop or server supply might be able to get away with passive PFC, which is not very complicated but tends to be bulky.

All desktop and server power supplies use active PFC at this point, because the cost of the much bulkier passive components is now higher than the cost of the active ones.

EDIT: apparently not quite, I went on Newegg and the non-80plus power supplies still have passive PFC.

Sure, simpler active PFC components are pretty cheap now. There isn't much to a valley-fill circuit, though. That should get you below the legal limit on harmonic distortion in most cases. I know it is still the standard PFC in lower-power fluorescent light ballasts.

HP chargers / bricks for their high end laptops are pure engineering marvels. http://www.terapeak.com/worth/genuine-hp-elitebook-8760w-877...

I looked inside an IBM laptop charger and it was considerably simpler than the Apple charger. Since it always outputs power, it doesn't include the microcontroller in the Apple charger. The other circuitry was somewhat simpler (it didn't output multiple voltages), and the IBM charger didn't go to as much effort to be compact.

> AC power enters the charger and is converted to DC. The PFC circuit (Power Factor Correction) improves efficiency by ensuring the load on the AC line is steady. The primary chops up the high-voltage DC from the PFC circuit and feeds it into the transformer. Finally, the secondary receives low-voltage power from the transformer and outputs smooth DC to the laptop.

I had a hard time reading this. It sounds like the transformer is getting DC power? Do transformers even work with DC power?

> The primary chops up the high-voltage DC from the PFC circuit and feeds it into the transformer.

It chops it up to AC for the transformer.

Ah, this makes sense. Do you know how the "chopping it up into AC"works?

I'm no expert so may be corrected, but I assume just an inverter https://en.wikipedia.org/wiki/Power_inverter

This transformer would be a flyback transformer therefore doesn't need to be driven by anything so hard-to-generate as a sine wave. It can be driven by a "switch" (MOSFET) at it's primary which is connected to DC.

https://en.wikipedia.org/wiki/Flyback_transformer#Operation_...

All switching power supplies (hence the name) are driven by either full-on or full-off ("switching") transistors. A "flyback" topology is only one of many possible ways to build a switching power supply, but as it's the simplest, it's the most common in low power supplies.

See the Switch−Mode Power Supply Reference Manual from ON Semiconductor for info on all the other possible ways to build a switching power supply.

I was wondering this too, I've never heard of a DC transformer. I thought AC-DC conversion circuits stepped down the voltage with a transformer prior to sending them through the full wave rectifier?

The drive transistors turn on and off at high speed to chop up the DC. You can think of these pulses as AC; they provide the changing magnetic field the transformer needs. Since this charger is a resonant converter, it's a bit more complex than most; the inductor-capacitor circuit resonates and the pulses turn into sinusoids.

now if they can just make it earthed by not lacquering the connector designed for that purpose to make it shiny... maybe macbooks everywhere will stop giving people shocks (!)

Double-insulated appliances don't need to be earthed.

a long time ago i used to work in a factory testing fairly low build quality computers, if i did their qa process on macbooks they would fail this 15 year old test because of this.

i know that us standards are often different to uk, europe and others in this regard. maybe it is safe and our standards are paranoid, but i don't enjoy electric shocks, no matter how small they are... and from talking to others, this is not an uncommon experience - at least on 2013 and newer macbooks using the UK version of the plug

A small amount of current leakage is actually normal in a well-designed switch-mode power supply, as odd as that may sound.

not into my body its not. at least based on my many years of using electrical devices - i've not seen this kind of problem on the same level that i can remember, except for the static build up on old CRT TVs.

There will be some kind of current into the "Ground" terminal on the output (i.e. your computer case) for most small switching power supplies (two-prong without separate protective earth pin). This current is caused by the "Y-Capacitor" which goes between the secondary ground/shielding and one of the power inputs.

http://electronics.stackexchange.com/questions/216959/what-d...

This is needed for proper EMI/RF immunity and because of this you often can measure the line voltage (or half of the line voltage, depending on how the Y capacitor is connected internally) on the output pins with a high-impedance multimeter.

No significant current can flow, though, because at the line frequency (50 or 60 Hz) the impedance of the Y capacitor (typically 1nF or so) is pretty high (2.5MOhm). For 230V, this would correspond to 0.1mA.

I wonder if its possible to run linux off a power adapter...

No implementation for the MSP430 as it stands, but I can't see why not.

https://en.wikipedia.org/wiki/%CE%9CClinux

MSP430's only have 64K of address space, which isn't enough to run even uCLinux.

But it is quite a lot for CP/M - https://en.wikipedia.org/wiki/CP/M

Eh, it's low even for CP/M. MSP430s have 64K of address space, not RAM. Even the smallest CP/M machines had that. A lot even had simplistic paging hardware to exceed that.

Depending on the model, it only has 512B of RAM, lol

I guess USB-C charger for newer MacBooks is even more complex. Still I wish Apple paid more attention to designing cables and connectors. In my case the cable broke within weeks and after a year the USB-C socket on the power supply became loose randomly disconnecting the cable :(

Amazing that today's laptop chargers have as much computational power as the original mac

Mine have always lasted for Macbooks, as I never take them out with me. Phones/iPads start fraying after a year or so if you chuck them in bags etc.

"plugged in, not charging" problems are very common with Macbooks. Maybe a simple charger would work better.

Can anyone give me a quick summary?

oh yes... a classic read. a perennial favorite!

Maybe add 2015 to the title. This same blog post has been linked a good amount before.

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