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iPad charger teardown: inside Apple's charger and arisky phony

This article is now available in Turkish iPad şarjının iç yapısı and Chinese [中文翻译版本] Apple iPad原装充电器拆解. 

 Apple sells their iPad charger for $19, while you can buy an iPad charger on eBay for about$3. From the outside, the chargers look the same. Is there a difference besides the price? Inthis article, I look inside real and counterfeit chargers and find that the genuine charger hasmuch better construction, power quality, and most importantly safety. The counterfeit turnsout to be a 5 watt charger in disguise, half the power of a genuine charger.

iPadCounterfeit

From the outside, the real charger (left) and counterfeit charger (right) are almost identical.If you look very closely, you can spot are a few differences in the text: The counterfeitremoved "Designed by Apple in California. Assembled in China" and the manufacturer"Foxlink"[1], probably for legal reasons. (But strangely, the counterfeit still says "TM and ©2010 Apple Inc.") The counterfeit charger displays a bunch of certifications (such as UL)that it doesn't actually have. As you will see below, there is no way it could pass safetytesting.

Opening up the chargers reveals big differences between them. The genuine charger on theleft is crammed full of components, fitting as much as possible into the case. The counterfeitcharger on the right is much simpler with fewer components and much more empty space.The Apple charger uses larger, higher-quality components (in particular the capacitors andthe transformer); below you will see that these have a big effect on power quality andsafety.

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 The components inside a real iPad charger (left) and a counterfeit charger (right).

One safety difference is obvious: the Apple charger has much more insulation. The upper(high-voltage) half is wrapped in yellow insulating tape. Some components are encased inshrink tubing, there are plastic insulators between some components, and some wires haveextra insulation. The counterfeit charger only has minimal insulation.

The build quality of the Apple charger is much higher. In the counterfeit charger, somecomponents are visibly crooked or askew. While this doesn't affect the circuit electrically, itindicates a lack of care in construction.

Flipping the boards over reveals that the circuitry of the genuine Apple charger is muchmore complex than the counterfeit. The Apple board is crammed with tiny surface-mountedcomponents in every available spot. The counterfeit board has a lot of empty space, with

 just a few components. Note the reddish insulating tape in the lower center of the Appleboard, another safety feature of the genuine charger.

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 The circuit board of a real iPad charger (left) and a counterfeit charger (right).

How the chargers work

Both the real and counterfeit chargers use similar flyback [2] switching power supply circuits.The switching power supply is the innovationthat allows these chargers to be so compact,unlike the heavy "wall warts" powering older consumer electronics. The principle of aswitching power supply is the power is switched on and off tens of thousands of times asecond, allowing it to provide the exact amount of power required with very little powerwasted as heat. In addition, the high frequencies allow the charger to use a small

transformer, unlike the bulky transformers used for 60 Hz AC.

Since the counterfeit charger is much simpler, it is easier to understand how it works and I'llexplain it first in reference to the picture below. The AC power enters through the whitewires in the upper left. It passes through a fusible resistor, which acts as a safety fuse.Below this, the bridge rectifier contains four diodes which convert the AC into DC (at about170 to 340 volts[3]). The input capacitor smooths out this power. The 4-pin controlIC[4] monitors the charger and uses the switching transistor to turn the high-voltage DC onand off 41,000 times per second. This chopped DC is fed into the primary winding of theflyback transformer. The transformer converts this to the desired high-current 5 volts. Theoutput diode produces DC, and the output capacitor smooths it out. Finally, the outputvoltage is available at the USB connector to power your iPad. A few components round out

the circuit. A feedback winding on the transformer provides voltage feedback to the controlIC. This winding also powers the IC; the IC power capacitor smooths out this power. Finally,the blue snubber [5] capacitor absorbs current spikes when the transistor is switched off .[6] 

Counterfeit

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 Inside a counterfeit iPad charger

The genuine iPad charger below operates on similar principles, although the circuit is moreadvanced. The AC input is on the lower right, and goes through a 2A fuse (in black

insulation for safety). The primary has much more filtering than in the counterfeit chargerwith a filter coil (common mode choke), inductor, and two large electrolytic capacitors. Thisincreases the cost, but improves the power quality. On the output side (left), the charger hastwo filter capacitors, including a high-quality aluminum polymer capacitor (with the magentastripe). The Y capacitors help reduce interference.[7] The tiny NTC temperature sensor letsthe charger shut down if it overheats. (I removed some of the charger's insulation to makethe components visible in this photo.)

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 Inside a genuine iPad charger.

On the other side of the circuit board, things get complicated in the Apple charger. Startingwith the AC input in the upper right, the charger includes additional input filters as well asspark gaps.[8] The latch release circuit[9] lets the charger reset quickly from faults. The control

IC[10] provides advanced control of the charger under varying conditions. (This IC is muchmore complex than the control IC in the counterfeit charger.) The current sense resistor letsthe IC monitor the current through the transformer and the line voltage resistors let the ICmonitor the input voltage (as well as initially powering-up the IC[9]). The protection circuituses the temperature sensor on the other side of the board to shut down if there is an over-voltage or over-temperature problem. [20] 

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 The circuit board inside a genuine iPad charger showing the components.

The secondary side includes some special features for power quality. The Y-capacitor filterworks with the Y capacitors to filter out noise. The output filter circuitry is more complexthan in the counterfeit. Note that the real charger has a ground connection, unlike thecounterfeit charger which has a plastic pin here.[11] 

Both chargers use resistors to put special voltages on the USB data lines [12] to indicate thecharger type, using Apple's proprietary system (details). (This is why iPads say "Charging isnot supported with this accessory" with some chargers.) Through these resistors thegenuine charger indicates that it is an Apple 2A charger, while the counterfeit indicates thatit is an Apple 1A charger. This shows that the counterfeit is really a 5W charger packagedas a 10W charger.

When looking at these circuits up close, it's easy to forget just how small the componentsare. The picture below shows one of the surface-mount components (a 0-ohm resisto r [13]) from the iPad charger. It is just to the left of Roosevelt's chin on the dime.

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 A zero-ohm resistor

Safety, or lack thereof

Safety probably isn't something you think about when you plug in your charger, but it'simportant. Inside the charger is 170 volts or more with very little separating it from your iPad

and you. If something goes wrong, the charger can burn up (below), injure you, oreven killyou. Devices such as chargers have strict safety standards [14] - if you get a chargerfrom a reputable manufacturer. If you buy a cheap counterfeit charger, these safetystandards are ignored. You can't see the safety risks from the outside, but by taking thechargers apart, I can show you the dangers of the counterfeit.

Counterfeit iPhone

 A Counterfeit iPhone charger that burned up. Photo by Anool Mahidharia. Used with permission

Creepage and clearance

The UL regulations[14] require safe separation between the high voltage and the low voltage.This is measured by creepage - the distance between them along the circuit board, andclearance - the distance between them through air. The regulations are complex, but ingeneral there should be at least 4mm between high-voltage circuitry and low-voltagecircuitry.

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 The iPad charger provides safe creepage and clearance distances between the primary high-voltage side (bottom)and secondary low-voltage side (top).

The image above shows how the genuine iPad charger's circuit board separates the highvoltage (bottom) from the low voltage (top). The happy face on the right marks an emptyregion that provides a safety gap between the primary and secondary. (This is a contrastwith the rest of the circuit board, which is crammed full of components.) This gap of 5.6mmprovides a comfortable safety margin. The happy face on the left marks a slot in the boardthat separates the low voltage and high voltage. The photo below shows how an insulatingfin is built into the case and through this slot to protect the USB connector. Additionalreddish-brown insulating tape goes through this slot, and the whole high-voltage section iswrapped in yellow insulating tape. The result is multiple layers of protection.

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The iPad charger case has a plastic fin that slides around the USB port to provide extra insulation.

The creepage distance on the counterfeit charger board below is scary - only 0.6 mmseparation between low and high voltage. The sad face on the right shows where a low-voltage trace is nearly touching the high-voltage trace below. (The ruler on the rightindicates millimeters.) The board isn't as bad as it could be: the happy face on the left

marks a slot cut in the circuit board under the transformer to increase the creepagedistance. But overall, this board is unsafe. If you use the charger in a humid bathroom and adrop of water condenses across the 0.6 mm gap, then zap!

Counterfeit

Dangerous creepage in a counterfeit iPad charger.

Safety in the transformer

For safety, the high-voltage and low-voltage sides of the charger must be electricallyisolated.[15] But obviously the electrical power needs to get through somehow. The flybacktransformer accomplishes this task by using magnetic fields to transfer the power without adangerous direct connection. Because the transformer is a large and relatively expensive

component, it is tempting to take safety and quality short cuts here. The genuinetransformer (left) is considerably larger than the counterfeit (right), which is a hint of betterquality and more power capacity. Disassembling the transformers shows that this is thecase.

iPadCounterfeit

The flyback transformers from an iPad charger (left) and a counterfeit charger (right). Dime and banana are for scale.

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The key safety requirement of the transformer is to separate the high-voltage windings fromthe low-voltage secondary winding, and the counterfeit charger fails here. The picturesbelow show the transformers after removing primary windings and insulating tape, revealingthe secondary winding. The wires look similar at first glance, but the the genuine charger(left) has triple-insulated wire while the counterfeit (right) is uninsulated except for a thinvarnish. The triple-insulated wire is an important safety feature that keeps the high voltageout even if there is a flaw in the insulating tape and in the wire's insulation. Also note theadditional black and white insulation on the wires where they leave the transformer. In thecounterfeit charger, the only thing separating the secondary winding from high voltage is theinsulating tape. If there is a flaw in the tape or the wires shift too far, then zap!

iPad

Counterfeit

The real charger provides much more power with much lessnoise

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Lab measurements of the output from the chargers shows a couple problems with thecounterfeit. First, the counterfeit turns out to provide at most 5.9W, not 10W. Second, theoutput voltage is extremely noisy and full of spikes.

The following voltage-vs-current graphs show the performance of the iPad charger (left) andcounterfeit charger (right) under increasing load. The line for the real charger goes muchfarther to the right, showing that the real charger provides much more current. By mymeasurements, the real charger provides a maximum of 10.1 watts, while the counterfeitcharger provides only 5.9 watts. The consequence is the real charger will charge your iPadalmost twice as fast. (For details on these graphs, see my article testing a dozen chargers.)The other thing to note is the line for the Apple charger is smooth and thin, while thecounterfeit charger's line is all over the place. This indicates that the power provided by thecounterfeit charger is noisy and low quality.

iPad

Counterfeit

The next pair of graphs shows the power quality. The yellow line shows the voltage. Thereal charger has a stable yellow thin line, while the counterfeit charger's output has largevoltage spikes. (I had to change the scale to get the output to fit on the screen, so thecounterfeit charger is actually twice as bad as it appears here.) The bottom of thecounterfeit charger's yellow line is wavy, due to 120 Hz ripple appearing in the outputvoltage.

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iPad

Counterfeit

The orange line shows the frequency spectrum of the output: lower is better, and higher isexponentially worse. The counterfeit spectrum is much higher in general, with a large spikeat the switching frequency. This shows that the counterfeit charger's power is worse acrossthe frequency spectrum.

You might wonder if the power quality actually matters. The biggest impact it has is ontouchscreen performance. The interference from bad power supplies is known to cause thetouchscreen to behave erratically.[16] If your screen malfunctions when plugged into acharger, this is probably the cause.

Inside the real charger's transformer

There's more inside the transformer that you'd expect. This section does a full teardown ofthe transformer from the genuine charger.

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iPad

The first photo above shows that underneath the the first layer of yellow insulating tape, alayer of copper foil is attached to the transformer's ferrite core to ground it. Next, removingthe ferrite core and more insulation reveals the double-stranded primary winding. The high-voltage input is fed into this winding.

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iPad

Underneath the primary winding and more insulating tape is the triple-stranded biaswinding, which provides feedback and power to the control IC. (In the photo, this windinghas been removed and is surrounding the transformer.) After removing more insulatingtape, the secondary winding of the transformer is visible. As discussed in the safety section,the secondary winding has triple-insulated wires and extra insulation where the wires leavethe transformer. The next layer of insulation (right) contains copper foil. This helps reduceinterference.

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Finally, the innermost layer of the iPad charger flyback transformer is the second half of theprimary winding (above). Splitting the primary winding into two layers is more expensive, but

results in a better transformer due to better coupling of the magnetic fields.

In comparison, the transformer of the counterfeit charger is much lower quality. (I haven'tincluded the pictures for reasons of space; click through to see them.) It simply has the biaswinding (pic), secondary winding (pic), and primary winding (pic) , separated by insulatingtape. Unlike the genuine transformer, the counterfeit saves cost by omitting the copper foillayers. The counterfeit also doesn't use the more expensive split, multi-stranded windingsthat the genuine charger uses. As discussed earlier, the secondary winding is plain copperwire, not triple-insulated wire, which is a significant safety flaw.

How does the iPad charger compare to the iPhone charger?

The iPad charger is considerably larger than the iPhone charger and provides twice thepower. In my detailed iPhone charger teardown I looked at the internals of the iPhonecharger. The iPhone charger (below) uses two circuit boards that combine to form a oneinch cube, which is impressive engineering. The iPhone and iPad chargers are both flybackswitching power supplies, but the feedback mechanisms are very different.[17] Overall, I likethe iPhone charger more than the iPad charger from a design standpoint, mainly because ofthe harder engineering challenge of cramming everything into a much smaller space.

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Schematics

In my iPhone charger teardown, I drew up a schematic of the charger, but for the iPadchargers I didn't need to do this. The genuine iPad charger is almost identical[18] tothe reference design schematic provided by iWatt. The counterfeit charger is almostidentical to the schematic in the DB02A controller datasheet. You can see from theschematics that the genuine charger has a much more complex circuit than the counterfeit.(Click the thumbnails below to get to the datasheets.)

iPad

Counterfeit

Is the Apple charger worth the price?

 Apple's charger is expensive compared to other chargers, but is a high quality product. Youshould definitely stay away from the cheap counterfeit chargers, as they are low quality and

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dangerous. Non-Apple name brand chargers are generally good quality according tomytests, with some better than Apple. If you want to get an Apple charger without the highprice, the best way I've found is to buy a used  one on eBay from a US source. I've boughtseveral for testing, and they have always been genuine.

I wrote earlier  about Apple's huge profit margins on chargers. Apple has since dropped theircharger prices from $29 to $19, which is more reasonable, but looking at the price of similarchargers from other manufacturers and the cost of components, I think Apple has a hugeprofit margin even at $19.[19] 

In any case, the iPad charger is an impressive piece of engineering with a lot of interestingcircuitry inside. The counterfeit charger is also impressive in its own way - it's amazing thata charger can be manufactured and sold for such a low price (if you don't care about safetyand quality). Overall, you mostly get what you pay for; even if you can't tell from the outside,there are big differences inside the case.

Notes and references

[1] Foxlink (Taiwan), Foxconn (Taiwan), and Flextronics (Singapore) are all manufacturersfor Apple with confusingly similar names. Foxconn is the company with controversy overemployee treatment; this charger is made by Foxlink, a different company. Interestingly, thechairmen of both companies are brothers and the companies do a lot of business with eachother. The companies state that they are entirely independent, though (statement, Foxlinkannual report). Foxconn and Flextronics are the world's #1 and #3 largest electronicsmanufacturing companies according to the MMI top 50 for 2013, while Foxlink is smaller.

[2] The chargers uses a flyback design, where the transformer operates "backwards" fromhow you might expect. When a voltage pulse is sent into the transformer, the output diodeblocks the output so there is no output - instead a magnetic field builds up in the

transformer. The transformer core has a tiny air gap to help store this field. When thevoltage input stops, the magnetic field collapses, transferring power to the output winding.Flyback power supplies are very common for low-wattage power supplies.

[3] You might wonder why the DC voltage inside the power supply is so much higher thanthe line voltage. The DC voltage is approximately sqrt(2) times the AC voltage, since thediode charges the capacitor to the peak of the AC signal. Thus, the input of 100 to 240 volts

 AC is converted to a DC voltage of 145 to 345 volts internally. This isn't enough to beofficially high voltage but I'll call it high voltage for convenience. According to standards,anything under 50 volts AC or 120 V dc is considered extra-low voltage and is consideredsafe under normal conditions. But I'll refer to the 5V output as low voltage for convenience.

[4] The counterfeit charger uses a DB02A controller IC. This controller only has four pinsand is in a TO-94 (SIP-4) package. (According to the official JEDEC standard, TO-94 isa bolt-like package for large SCRs. It's a puzzle why some companies use TO-94 todescribe 4-pin inline packages.) According to the datasheet (Chinese), the chip is for500mA-1000mA chargers, which explains why the counterfeit charger only produces 5watts, instead of the 10 watts an iPad charger is supposed to produce. This controller isvery inexpensive,available for ¥ 0.35 (about 6 cents).

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I couldn't find any US chips similar to this chip, even after a lot of searching; it appears to bea Chinese design with datasheets only in Chinese, manufactured by "Fine Made" ShenzhenFuman Electronics. Since the chip only has four pins, I expected it to be a trivial RingingChoke Converter (RCC) circuit with just a couple transistors inside the chip - but I cracked itopen with Vise-Grips and it turns out to be a fairly complex chip. I took a picture through amicroscope of the IC die, which is about 1 mm across. One interesting feature is the manywhite pads around the outside of the die, which are used to blow fuses to trim variousresistances in the chip. I wasn't expecting to see this level of quality and sophistication. Thedie has the label "N7113 802" at the right; I don't know what this indicates. Three of the fourwires connect in the lower left, and the fourth in the lower right.

Die photo of the DB02A SMPS controller chip used in the counterfeit charger.

[5] When a diode or transistor switches, it creates a voltage spike, which can be controlledby a special snubber or clamp circuit. For a lot of information on snubbers and clamps,see Passive Lossless Snubbers for High Frequency PWM Conversion and SwitchmodePower Supply Reference Manual. 

[6] In the counterfeit charger, the switching transistor is a ALJ 13003 NPN power transistor(datasheet), apparently made by Shenzhen LongJing Microelectronics Co. This transistor isa version of Motorola's MJE 13003 switchmode transistor which was introduced in 1976(MJE  indicates power device in a plastic package). The bridge rectifier is a B6M(datasheet). The output diode is a SR260 Schottky barrier rectifier.

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[7] The iPad charger uses special Y-capacitors to bridge the high-voltage and low-voltagesides of the charger. This capacitor helps reduce EMI interference, and is speciallydesigned to avoid any safety hazard. It does, however, pass a tiny amount of electricity - ifyou feel a tingle from your charger, these capacitors are probably the cause. For moreinformation on X and Y capacitors, see Kemet's presentation and Designing low leakagecurrent power supplies. 

[8] The iPad has two spark gaps next to inductor L1 (the input AC common mode choke). Icouldn't find a lot of information on this sort of spark gap, but one example of it isan Infineon SMPS design, where similar spark gaps are designed to discharge accumulatedcharge for a 3KV lightning surge test.

[9] The Apple charger includes a "latch release circuit". If there is a fault, the control IC willshut down the charger until power is removed. However, after unplugging a charger, theinput capacitors may store power for many seconds. (You may have seen LEDs remainilluminated for several seconds after unplugging devices.) The latch release circuit ensuresthat the charger will reset properly even if you plug it back in quickly. It does this by

providing a separate diode bridge for the charger's power - this circuit has a much smallercapacitor, so it will power off quickly. (See the schematic for details.) This seems like over-engineering to me, adding extra circuitry for this rare case.

In normal use, by the way, the control IC is powered by the transformer's feedback winding.But if the control IC isn't running, the transformer won't work, leading to a chicken-and-eggsituation. The solution is a startup power path where the control IC gets enough power fromthe AC input to start up, and then switches to the transformer.

[10] The genuine charger uses a complex control chip manufactured by iWatt, the 1691. This chip monitors the input line voltage, the current through the transformer, and the

voltage feedback from the transformer. It controls the switching frequency and length oftime the power is switched on, with different behavior under no load, low load, and highload, as well as constant monitoring for faults. A detailed presentation on the iW1691is here. This chip sells for about 30 cents, but I expect Apple gets a better price.

[11] The real charger has a metal ground pin that connects to the power plug, while thecounterfeit has a plastic pin. This is one difference between the chargers that is visibleexternally if you slide the power plug off the charger. Ironically, the US plug doesn't use theground connection, so this is one safety issue that doesn't make any difference in practice.

[12] Apple uses a proprietary technique for the charger to indicate to the device what kind ofcharger it is. Different types of Apple chargers use resistances to put different voltages on

the USB D+ and D- pins. For details on USB charging protocols, see my earlier references. 

[13] While it would be nice to find superconductors inside the charger, unfortunately thezero-ohm resistor is a bit more than 0 ohms. While this resistor may seem pointless, itallows the manufacturers to substitute a resistor later if different transistors require it.

[14] The outside of the charger has the slightly mysterious text: "For use with informationtechnology equipment". This indicates that the charger is covered by the safety standard  UL

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60950-1, which specifies the various isolation distances required. For a brief overview ofisolation distances, see i-Spec Circuit Separation and some of my earlier references. 

[15] Only a few special components can safely bridge the gap between the high voltageside of the charger and the low voltage side. The most obvious is the transformer. Y-capacitors can also bridge the primary and secondary side because they are designed notto pass dangerous currents, and not to short out if they fail. Optoisolators use a light signalto provide feedback between the circuits in an iPhone charger, but are not used in the iPadcharger.

[16] For an explanation of why the noisy output from cheap chargers messes uptouchscreens, see Noise Wars: Projected Capacitance Strikes Back. The article discusseshow capacitive touchscreen ICs need to sense pico-Coulombs of charge, which is verydifficult when AC noise is present. The article blames touchscreen problems on aftermarketlow cost chargers.

[17] The biggest difference between the iPhone charger and the iPad charger is the

feedback used to regulate the voltage. The iPhone charger measures the output voltagewith a TL431 chip and sends a feedback signal to the control IC via an optoisolator. TheiPad charger avoids these components by using primary-side regulation. Instead ofmeasuring the actual output voltage, the iPad control IC looks at the voltage in the feedbackwinding, which should approximately match the output voltage.

[18] I noticed only a few significant differences between the iPad charger and iWatt'spublished 1691 charger reference design. This probably means iWatt did most of the designwork for Apple.

Comparing the actual charger with the reference design shows a few filtering

improvements. The charger has RC snubbers the input bridge rectifier (a rare feature alsoin the iPhone charger ). The charger has an extra diode on the secondary for filtering, aswell as a (zener?) diode in the switching transistor drive circuit. The iPad charger uses twoY-capacitors instead of one, and a R/C filter attached to the Y-capacitor on the secondaryside. The charger connects line ground to secondary ground through a resistor. Thereference design doesn't show the USB data resistors [12]. 

[19] Some people think that I'm ignoring Apple's cost of designing chargers when figuringtheir large profit margin. First, if you spend $2 million on design and manufacture 200 millionchargers, then design adds only one cent to the cost per charger. Second, iWatt's designersdeserve credit for the complex control chip and the reference design, which is most of thedesign work.

[20] For those interested in the components, the iPad charger's primary diodes (F6w) are1.5A 60V Schottky Barrier Diodes (datasheet). The "T3" diodes are fast switching diodes(datasheet). The switching transistor is an Infineon SPA04N60C Cool MOS® 650V powertransistor (datasheet). The bridge rectifier is a bridge: MB10S CD 0.5A bridge rectifier withhigh surge capacity (datasheet). The component in the protection circuit that looks like atransistor is a BAV70 dual high-speed switching diode (datasheet). The output diode is aSBR10U45SP5 10A super barrier rectifier (datasheet). The Y capacitors are 220pF 250V.

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The input capacitors are Samxon 10µFand 4.7µF 400v electrolytics. The output capacitorsare a Koshin KLH 820µF 6.3V aluminum electrolytic, and a 820 µF 6.3V X-CONULRaluminum polymer capacitor (which is more expensive than a regular electrolytic, butfilters better because of its lower  ESR).