Apple and other USB charger secrets

Everybody seems to be saying that you can’t charge Apple devices with normal USB power supplies. You need a special power supply from Apple or approved by Apple. I saw this kind of discussion at slashdot some time ago.

Usually, device makers need to sign a confidentially agreement with Apple if they want to say their charger ‘works with iPhone / iPod,’ and they’re not allowed to talk about how the insides work. I hate when manufacturers do crap like this to keep peripherals locked into a more profitable licensing agreement. Apples tendency toward total control is one of the things i don’t like about them. And many other manufacturers are just as bad. I wish companies would back off and be more open and/or use standard micro USB chargers.

The mysteries of Apple device charging article includes a 7-minute video we explore the mysteries of Apple device charging. The secret of Apple chargers is simple: just few resistors. If you don’t put these secret resistors on the data lines too, you get the dreaded Charging is not supported with this accessory. Those resistors like a way to signal to the iPhone that it can go ahead and “fast charge” by pulling 1A, or “slow charge” by pulling 0.5A. The iPhone needs to do a power negotiation to determine if the port is capable of providing 1000ma of power, because the upper-limit of a standard USB port is 500 mA. They just didn’t tell anyone about how to do that. I get why the resistors were initially added but I’m not understanding why it needs to be a trade secret.


There is nothing to stop them just drawing the 500mA if the right sort of charger is not detected. Refusing to charge at all unless the licensed parts are present is pure market control, nothing else. Here is the resistor configuration for 500 mA charging:


Resistance is Futile. The The mysteries of Apple device charging article demonstrates how anyone can make their own chargers that work with iPhone 4, 3Gs, etc. The pictures on this blog posting are from that article.

Apple devices are not the only one USB charged devices that can have some problems with USB chargers. So here are some resources on USB charging in general.

USB As A Power Source article gives an introduction USB Power Form.

European Commission has reached a voluntary agreement with some of the biggest names in the electronics industry to introduce a common charger for cell phones that fits all models. Information on this USB charging connector is available at USB Approved Class Specification Documents document directory. Read also Battery Charging v1.1 Spec and Adopters Agreement document.

Dealextreme USB charger discussion posting says that USB standard has 4 lines (+5V, ground and +/- data lines). Most USB chargers let the data lines float. Technically, the USB standard says that a USB charger should set the two data lines to specific voltages (~ 2V) to indicate how much power it can provide (I have not verified that from standards yet). The recent iPhones will not charge if the data lines are set incorrectly (i.e. not according to the USB standard).

USB Charging Guide comment: I believe having the data pins connected to each other is in the latest USB specification for charging. I had to interconnect the D+ and D- pins inside my USB AC charger to get it working with my Zune. Perfectly according specs but frustrating enough.

Wikipedia USB article: The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire from which connected USB devices may draw power. The specification provides for no more than 5.25 V and no less than 4.75 V (5 V±5%) between the positive and negative bus power lines. For USB 2.0 the voltage supplied by low-powered hub ports is 4.4 V to 5.25 V.

A unit load is defined as 100 mA in USB 2.0, and was raised to 150 mA in USB 3.0. A maximum of 5 unit loads (500 mA) can be drawn from a port in USB 2.0, which was raised to 6 (900 mA) in USB 3.0.
All devices default as low-power but the device’s software may request high-power as long as the power is available on the providing bus.

In Battery Charging Specification, new powering modes are added to the USB specification. A host or hub Charging Downstream Port can supply a maximum of 1.5 A when communicating at low-bandwidth or full-bandwidth, a maximum of 900 mA when communicating at high-bandwidth, and as much current as the connector will safely handle when no communication is taking place (USB 2.0 standard-A connectors are rated at 1500 mA by default).

A Dedicated Charging Port can supply a maximum of 1.8 A of current at 5.25 V. A portable device can draw up to 1.8 A from a Dedicated Charging Port. The Dedicated Charging Port shorts the D+ and D- pins with a resistance of at most 200Ω. The short disables data transfer, but allows devices to detect the Dedicated Charging Port and allows very simple, high current chargers to be manufactured. The increased current (faster, 9 W charging) will occur once both the host/hub and devices support the new charging specification.

Without negotiation, the powered USB device is unable to inquire if it is allowed to draw 100 mA, 500 mA, or 1 A. Some non-standard USB devices use the 5 V power supply without participating in a proper USB network which negotiates power draws with the host interface

In most cases, these items contain no digital circuitry, and thus are not Standard compliant USB devices at all. This can theoretically cause problems with some computers; prior to the Battery Charging Specification, the USB specification required that devices connect in a low-power mode (100 mA maximum) and state how much current they need, before switching, with the host’s permission, into high-power mode.

USB Charging Guide tells some more details on mini-USB plug: the mini-USB plug actually has 5 pins in it. This can be important as the extra pin (Pin 4) USB_ID is usually either connected to ground or left floating. Sometimes a pull up resistor needs to be added to from the USB_ID to Pin 1 (VDD) to select “Device Mode” rather than “Host Mode”. This resistor is in the device side plug as the USB_ID pin is not wired through to the PC side connector. The good news is that quite a few USB cables have this. So sometimes you can get round the not charging problem simply by trying out different leads and one may work rather than buying the manufacturers “special” cable. On some Creative players you can also solve this by pulling down both data lines (with 2x15k resistors) at the source to emulate what the host (PC) does when setting line speed. This is not so common.

So the current state of USB charging is a little bit of mess…


  1. Tomi Engdahl says:

    Jon Porter / The Verge:
    EU’s proposal forces companies to make fast-charging standards interoperable and “unbundles” charger sales; if adopted, companies will have 24 months to comply — With the aim of reducing e-waste — The European Commission, the executive arm of the European Union …

    EU proposes mandatory USB-C on all devices, including iPhones
    With the aim of reducing e-waste

    The European Commission, the executive arm of the European Union, has announced plans to force smartphone and other electronics manufacturers to fit a common USB-C charging port on their devices. The proposal is likely to have the biggest impact on Apple, which continues to use its proprietary Lightning connector rather than the USB-C connector adopted by most of its competitors. The rules are intended to cut down on electronic waste by allowing people to re-use existing chargers and cables when they buy new electronics.

    In addition to phones, the rules will apply to other devices like tablets, headphones, portable speakers, videogame consoles, and cameras. Manufacturers will also be forced to make their fast-charging standards interoperable, and to provide information to customers about what charging standards their device supports. Under the proposal, customers will be able to buy new devices without an included charger.

  2. Tomi Engdahl says:

    Associated Press:
    European Commission proposes legislation mandating USB-C charging for mobile devices, citing electronic waste; Apple is the main USB-C holdout

    One to charge them all: EU demands single plug for phones

    The European Union announced plans Thursday to require the smartphone industry to adopt a uniform charging cord for mobile devices, a push that could eliminate the all-too-familiar experience of rummaging through a drawer full of tangled cables to find the right one.

    The European Commission, the bloc’s executive arm, proposed legislation that would mandate USB-C cables for charging, technology that many device makers have already adopted. The main holdout is Apple

  3. Tomi Engdahl says:

    Commission proposes a common charging solution for electronic devices – Questions and Answers

  4. Tomi Engdahl says:

    Why Wait For Apple? Upgrade Your IPhone With USB-C Today!

    Apple iPhones ship with the company’s Lightning cable, a capable and robust connector, but one that’s not cheap and is only useful for the company’s products. When the competition had only micro-USB it might have made sense, but now that basically all new non-fruity phones ship with USB-C, that’s probably the right way to go.

    [Ken Pilonell] has addressed this by modifying his iPhone to sport a USB connector. The blog post and the first video below the break show us the proof of concept, but an update in the works and a teaser video show that he made it.

  5. Tomi Engdahl says:

    Applelta ensimmäinen GaN-pikalaturi

    Applen uusin tuotejulkistus piti sisällään uudet M1 Pro- ja M1 Max -prosessorit sekä näiden vauhdittamat uudet 14- ja 16-tuumaiset Macbook Pro -läppärit. 16-tuumaisen huippumallin mukana tulee 140-wattinen laturi, joka lupaa hyvää Applen tulevillekin latureille.

    ChargerLab on ottanut tehtäväkseen uutuuslaturin purkamisen ja analysoinnin. Purku osoittaa, että ensimmäistä kertaa missään laitteessa Applen on käyttänyt gallium-nitridipohjaisia tehokomponentteja. Tämän ansiosta on päästy 140 watin huipputehoon.

    Laturi tukee USB-latauksen uutta tehonsyötön PD3.1-standardia. Sen avulla läppäriin voidaan syöttää USB-kaapelia pitkin 28 voltin ja 5 ampeerin virtaa 140 watin teholla. Apple-tyyliin kaapeli liitetään tietokoneeseen toki MagSafe-liittimellä.

    Latest Teardown of Brand New Apple 140W USB-C GaN Charger

  6. Tomi Engdahl says:

    The 7805 is a fixed voltage linear regulator that outputs 5V at up to 1A current. That is about the same current many lower power USB chargers give out. One 7805 works as low speed charger.

    Paralleling multiple linear voltage regulators like 7805 is a bad idea. It does not work well.

    LM78S05 IC. it is a 5v regulator IC with 2A current output.

    For charging to work quickly there are also other tricks that just having high current output regulator

  7. Tomi Engdahl says:

    Kännyköistä tuttu huippunopea laturitekniikka tulee läppäreihin

    GaN eli galliumnitridi on seuraavan sukupolven tehokomponenttien tekniikka, joka toimii jopa 20 kertaa nopeammin kuin vanha piipohjaiset laturit ja mahdollistaa jopa 3 kertaa suuremman lataustehon 40 prosenttia pienemmällä tehonkulutuksella ja puolta pienemmässä koossa. Nyt tämä älypuhelimiin ensin tullut tekniikka on laajenemassa kannettaviin tietokoneisiin ja jopa datakeskusten palvelimiin.

    Navitas Semiconductor on GaN-piirien pioneeri. Nyt se ilmoittaa, että Dell on valinnut sen GaNFast-virtapiirit Latitude 9000 -sarjan kannettavien tietokoneiden pikalataukseen.

    Uusi Dellin 60 watin pikalaturi korvaa vanhan piipohjaisiin komponentteihin pohjautuvan laturin. Läppärin GaNFast-laturi on kooltaan vain 66 x 55 x 22 millimetriä ja painaa 175 g. Se on 50 prosenttia pienempi ja 25 prosenttia kevyempi kuin edeltäjänsä.

  8. Tomi Engdahl says:

    RapidCharge™ Controllers Prevent Fast Charger Hacking

    Recent news stories report that some fast chargers designed with MCUs can be easily hacked. When users connect their devices to these fast chargers via the USB cable, hackers may be able to compromise the charger by sourcing more power than the device can safely handle, damaging or even destroying the device. Hackers can alter the firmware of fast charge devices in order to deliver extra voltage and damage connected equipment . . .

    Designers can try to add more code in the MCU to prevent hacker modifications, but only if the MCU has the option to be updated. Or, they can try to add overload protections in the devices for which the chargers are designed. These methods are hardly ideal.

    Hard-Wired State Machine Approach

    A simpler and lower cost approach is to design fast chargers and power supplies without MCUs and firmware, and instead use a hard-wired state machine approach.

    Fast chargers and power supplies designed with Dialog’s Rapid Charge™ controllers cannot be hacked, because they are hard-wired state machines, so there is no firmware that can be accessed and corrupted. And, with a hard-wired state machine, you won’t need to spend extra time and expense to harden firmware or add overload protections.

    BadPower attack corrupts fast chargers to melt or set your device on fire

    Attackers can alter the firmware of fast charger devices to deliver extra voltage and damage connected equipment.

  9. Tomi Engdahl says:

    What if I charge a charger?

    Just a stupid experiment
    Don’t try this at home.

  10. Tomi Engdahl says:

    Fooled by a phone charger?? Bryan Saint on Penn & Teller: Fool Us!

    Can this magician fool Penn and Teller just by charging Penn’s phone? Watch what Bryan Saint does on Penn & Teller: Fool Us!

    On the season 5 finale of Penn & Teller: Fool Us (S5, E13 “Let’s Hear it for the Kids), Charlotte NC magician Bryan Saint brings rope magic into the 21st century by using a phone charger. In Penn & Teller’s own words, “Rope tricks don’t mean much anymore; this means everything.” Bryan then borrows Penn Jillette’s phone and adds an interesting twist. Check out what happens!

  11. Tomi Engdahl says:

    Apple rimpuilee EU:n laturipäätöstä vastaan

    Euroopan komissio esitti viime syyskuussa aloitteen, joka tähtää yhden laturistandardin tuomiseen älypuhelimiin ja muihin kannettaviin laitteisiin. Uusimpien tietoja mukaan Apple ei ole ainakaan seuraavassa iPhone 14 -sarjassa luopumassa omasta Lightning-liitännästään.

    Apple on julkisesti kommentoinut EU:n ministerineuvostossa tammikuussa vahvistettua kantaa lakiehdotukseen sanomalla, että EU:n toiminta haittaa kuluttajia ja estää innovaatioita. Tähän kannattaa toki suhtautua varauksella, sillä Apple on muissa tuotteissaan (iPad ja läppärit) tukenut USBC-latausta jo pitkään.

    Helpolla Apple ei ole luopumassa Lightning-liitännästä älypuhelimissaan. Nykyisissä laitteissa käytetään liitäntää, joka perustuu USB 2.0 -tekniikkaan.

    Tiettävästi Apple aikoo nopeuttaa iPhone 14:n liitännän USB 3. -vauhtiin eli 5 gigabittiin sekunnissa. Tämä miellyttänee iPhone-käyttäjiä, ärsyttänee EU:ta ja tarkoittaa, että Lightning säilyy iPhonen liitäntänä vielä ainakin vuoden verran pidempään.

  12. Tomi Engdahl says:

    Natasha Lomas / TechCrunch:
    The European Parliament’s consumer protection committee votes 43 to 2 for a USB-C consumer electronics charging standard, ahead of a full parliament vote in May — European Union lawmakers have taken a step closer to agreeing rules to standardize how a range of mobile gadgetry is charged.

    MEPs vote to expand scope of common charger rules
    Natasha Lomas

  13. Tomi Engdahl says:

    Sami Fathi / MacRumors:
    Kuo: Apple will switch to USB-C for the iPhone 15 in the second half of 2023, improving transfer and charging speeds — Apple will ditch its proprietary Lightning port and switch to USB-C on all or possibly some models of the iPhone 15 lineup destined to launch in the second half of 2023, Apple analyst Ming-Chi Kuo said today.

    Kuo: iPhone 15 to Switch From Lightning to USB-C in 2023
    Wednesday May 11, 2022 3:12 am PDT by Sami Fathi

    Apple will ditch its proprietary Lightning port and switch to USB-C on all or possibly some models of the iPhone 15 lineup destined to launch in the second half of 2023, Apple analyst Ming-Chi Kuo said today.

    Since the ‌iPhone‌ 5, Apple has kept the Lightning port on the ‌iPhone‌, despite much of the industry moving to USB-C. In a tweet today, Kuo said that the latest supply chain survey indicates that Apple will ditch Lightning in favor of USB-C in 2023. Kuo noted that USB-C would improve transfer speeds on the ‌iPhone‌ and improve charging speeds.

    Kuo had previously said that Apple would be sticking with Lightning on the ‌iPhone‌ for the “foreseeable future,” saying that switching to USB-C would be harmful to Apple’s MiFi business and has lesser waterproof specification. Now, Apple has reportedly changed its tone. One possible reason for Apple’s change in heart is pressure being placed upon it by the EU.

  14. Tomi Engdahl says:

    Common charger: MEPs agree on proposal to reduce electronic waste

    Fewer redundant cables and chargers: good for environment and consumers
    USB Type-C port as new standard for portable device
    MEPs also want harmonisation for wireless charging

    MEPs support a common charger for portable electronic devices, reducing e-waste and making the use of different mobile phones, tablets and digital cameras more convenient.

    On Wednesday the Internal Market and Consumer Protection Committee adopted its position on the revised Radio Equipment Directive with 43 votes in favour (2 against).

    The new rules would make sure consumers no longer need a new charger and cable every time they purchase a new device, and can use one charger for all of their small and medium-sized electronic gadgets. Mobile phones, tablets, digital cameras, headphones and headsets, handheld videogame consoles and portable speakers, rechargeable via a wired cable, would have to be equipped with a USB Type-C port, regardless of the manufacturer. Exemptions would apply only for devices that are too small to have a USB Type-C port, such as smart watches, health trackers, and some sports equipment.

    This revision is part of a broader EU effort to address product sustainability, in particular of electronics on the EU market, and to reduce electronic waste.

    Clear information on charging

    MEPs also want to see clear information and labelling on new devices about charging options, as well as whether a product includes a charger. This would, they say, help to avoid confusion and ease purchasing decisions for consumers that often own several different devices and do not always need additional chargers.

  15. Tomi Engdahl says:

    Common charger: MEPs agree on proposal to reduce electronic waste

    Fewer redundant cables and chargers: good for environment and consumers
    USB Type-C port as new standard for portable device
    MEPs also want harmonisation for wireless charging

  16. Tomi Engdahl says:

    Jon Porter / The Verge:
    EU lawmakers reach an agreement on legislation that will mandate USB-C on smartphones and other electronic devices, starting in autumn 2024, to reduce e-waste

    USB-C will be mandatory for phones sold in the EU ‘by autumn 2024’
    A major blow to Apple’s Lightning port

    European Union lawmakers have reached an agreement on legislation that will force all future smartphones sold in the EU — including Apple’s iPhone — be equipped with the universal USB-C port for wired charging by fall 2024. The rule will also apply to other electronic devices including tablets, digital cameras, headphones, handheld video game consoles, and e-readers.

    The legislation has been under consideration for years, but an agreement on its scope and details was reached this morning following negotiations between different EU bodies.

    The European Parliament’s Committee on Internal Market and Consumer Protection announced the news in a tweet ahead of a press conference due to take place at 12:30 CEST (6:30AM ET) later today. The legislation does still need to be approved by the EU Parliament and Council later this year, but this appears to be more of a formality than anything else. In a press release, the European Parliament stated the law would be in place “by autumn 2024.”

    “Today we have made the common charger a reality in Europe!”

    The rules are an attempt to cut down on e-waste in the EU by making chargers for electronic devices interoperable. In the future, lawmakers hope that phones won’t need to come with a charger in the box because buyers will already have the appropriate cable and wall charger at home. The EU estimates that the rules could save consumers 250 million euros per year on “unnecessary charger purchases” and cut down on around 11,000 tonnes of e-waste annually.

    The agreement would have the biggest impact on Apple, which is the only major smartphone manufacturer to still use a proprietary port instead of USB-C. In 2021, Apple sold 241 million iPhones globally, of which about 56 million were sold in Europe. The EU’s press release specifically says the rules apply to devices “that are rechargeable via a wired cable,” meaning a device that only charges wirelessly would not need to be fitted with a USB-C port.

    The European Commission announced the current plans for the legislation last September, but the bloc’s efforts to force manufacturers to use a common charging standard go back over a decade. In the years since, Android manufacturers have converged upon micro USB and then USB-C as the common charging standard of choice, while Apple went from offering phones with its proprietary 30-pin connector to Lightning.

    Apple has pushed back against the EU’s attempts to force it to use USB-C on its phones. “We remain concerned that strict regulation mandating just one type of connector stifles innovation rather than encouraging it, which in turn will harm consumers in Europe and around the world,” a spokesperson told Reuters last year. It’s also argued that forcing a switch to USB-C would create e-waste rather than reduce it, because it would make its existing ecosystem of Lightning accessories redundant.

  17. Tomi Engdahl says:

    Deal on common charger: reducing hassle for consumers and curbing e-waste

    One single charger for all small and medium-sized portable electronic devices
    Charging speed harmonised for devices that support fast charging
    Buyers can choose whether to purchase new device with or without charging device

    By autumn 2024, USB Type-C will become the common charging port for all mobile phones, tablets and cameras in the EU, Parliament and Council negotiators agreed today.

    The provisional agreement on the amended Radio Equipment Directive, establishes a single charging solution for certain electronic devices. This law is a part of a broader EU effort to make products in the EU more sustainable, to reduce electronic waste, and make consumers’ lives easier.

    These new obligations will lead to more re-use of chargers and will help consumers save up to 250 million euro a year on unnecessary charger purchases. Disposed of and unused chargers are estimated to represent about 11,000 tonnes of e-waste annually.

  18. Tomi Engdahl says:

    Trilogisopu yleislaturista, tavoitteena vähentää elektroniikkaromun määrää

    Yksi laturi kaikille pienille ja keskikokoisille kannettaville laitteille
    Pikalataamisen nopeus harmonisoitaisiin
    Ostaja voi valita, ostaako laitteen laturin kanssa vai ilman

    EU-parlamentin ja neuvoston neuvottelutuloksen myötä kaikki EU:ssa syksyn 2024 jälkeen myytävät matkapuhelimet, tabletit ja kamerat on voitava ladata USB-C-latureilla.

    Alustava sopu radiolaitedirektiivin uudistuksesta tarkoittaa, että tiettyjä elektroniikkalaitteita ladataan jatkossa samalla laturilla. Uudistus on osa EU:n pyrkimystä parantaa tuotteiden, erityisesti elektroniikan, ympäristöystävällisyyttä, vähentää elektroniikkaromua ja helpottaa kuluttajien elämää.

    Press conference by Alex AGIUS SALIBA, rapporteur on the outcome of the trilogue on common charger

  19. Tomi Engdahl says:

    EU ottaa käyttöön yleislaturin
    EU on päässyt yhteisymmärrykseen yleislaturin käyttöönotosta.

    Euroopan parlamenttia ja Euroopan neuvosto ovat ilmoittaneet, että EU:ssa otetaan käyttöön yleislaturi, jossa on USB-C-liitäntä. Käytännössä ladattavien elektroniikkalaitteiden on siis tuettava USB-C-johdolla tapahtuvaa latausta.

    Uusi asetus ei koske laitteita, joihin USB-C-porttia ei voi sisällyttää laitteen koon vuoksi. Näihin lukeutuvat esimerkiksi älykellot ja aktiivisuusrannekkeet.

    Uudistuksen taustalla on tavoite elektroniikkajätteen määrän vähentämisessä, kun eri laitteiden mukana ei toimiteta vain niille tarkoitettua laturia. Lisäksi kuluttajan ei tarvitse hankkia erikseen uutta laturia, kun hänen vanha laturinsa toimii myös uuden laitteen kanssa.

    Matkapuhelimet, tabletit, e-lukijat, nappikuulokkeet, digikamerat, kuulokkeet, kädessä pidettävät videopelikonsolit ja kannettavat kaiuttimet, jotka ovat ladattavissa langallisella kaapelilla, on varustettava USB-C-portilla valmistajasta riippumatta”, tiedotteessa kerrotaan.

  20. Tomi Engdahl says:

    Yhteislaturi tulee – tämä on pian EU:n ainoa sallittu laturipää

  21. Tomi Engdahl says:

    Apple 10W USB charger failure analysis and repair

    Analyzing a faulty Apple 10W USB charger. Showing what’s inside, finding the faulty component, fixing the charger, showing some oscilloscope waveforms and testing various components (capacitors, a diode, transistor, inductor, resistor…).

  22. Tomi Engdahl says:

    Dual Power Supply In A Pinch

    The ones I had used the Injoinic IP2721 USB-C power delivery chip, commonly used in many of these boards. Mine had been sold pre-configured for certain output voltages, but they were easy to re-jumper to the voltages I needed, +5 VDC and +20 VDC. The most challenging aspect was physically using them — they are the size of a fingernail. This version had through-hole output pads on 0.1″ centers, so I decided to solder them to the base of a standard MTA pin header. A few crimps later and I was up and running, along with the requisite pair of USB-C cables and power adapters.

  23. Tomi Engdahl says:

    Usb charging circuit – Why are both data pins shorted?

    The original USB 1.X and 2.0 standards defined the maximum output current of a USB port to be 500mA. Since that is a lot less than modern smart phones need, non standardized methods have evolved.

    So in some circuits you find online the data pins are shorted, in others they have a 200Ohm resistor in between them and in Apple devices you’ll need a voltage divide from +5V to ground.

  24. Tomi Engdahl says:

    Reverse Engineering The Apple Lightning Connector

    A frequent contributor to the hacker community, [stacksmashing] has prepared an excellent instructional video on reverse engineering Apple’s Lighting connector proprietary protocol. The video begins by showing how to gain physical access to the signals and hooking them up to a logic analyzer. He then notes that the handshaking uses only a single signal and proposes that Apple isn’t going to re-invent the wheel (perhaps a risky assumption). Using a ChatGPT search, obligatory these days, we learn that Dallas Semiconductor / Microchip 1-wire is probably the protocol employed.

    The secrets of Apple Lightning – Part 1

  25. Tomi Engdahl says:

    [Big Clive] picked up a keychain battery to charge his phone and found out that it was no bargain. Due to a wiring mistake, the unit was wired backward, delivering -5 V instead of 5 V. The good news is that it gave him an excuse to tear the thing open and see what was inside. You can see the video of the teardown below.

    The PCB had the correct terminals marked G and 5 V, it’s just that the red wire for the USB connector was attached to G, and the black wire was connected to 5 V. Somewhat surprisingly, the overall circuit and PCB design was pretty good. It was simply a mistake in manufacturing and, of course, shows a complete lack of quality assurance testing.

  26. Tomi Engdahl says:

    For versions 1 of USB The spec says 5V +/- 5%, so you should design to accept 4.75V to 5.25V.

    For USB 2.0 the spec says: • The voltage supplied by high-powered hub ports is 4.75 V to 5.50 V. • The voltage supplied by low-powered hub ports is 4.4 V to 5.50 V.


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