How Chargers Work

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? In this article, I look inside real and counterfeit chargers and find that the genuine charger has much better construction, power quality, and most importantly safety. The counterfeit turns out to be a 5 watt charger in disguise, half the power of a genuine charger. iPad Counterfeit 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 counterfeit removed "Designed by Apple in California. Assembled in China" and the manufacturer "Foxlink" , 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 safety testing. [1] Opening up the chargers reveals big differences between them. The genuine charger on the left is crammed full of components, fitting as much as possible into the case. The counterfeit charger 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 and the transformer); below you will see that these have a big effect on power quality and safety. iPad Counterfeit 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 in shrink tubing, there are plastic insulators between some components, and some wires have extra insulation. The counterfeit charger only has minimal insulation. The build quality of the Apple charger is much higher. In the counterfeit charger, some components are visibly crooked or askew. While this doesn't affect the circuit electrically, it indicates a lack of care in construction. Flipping the boards over reveals that the circuitry of the genuine Apple charger is much more complex than the counterfeit. The Apple board is crammed with tiny surface-mounted components 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 Apple board, another safety feature of the genuine charger. iPad Counterfeit the output voltage is available at the USB connector to power your iPad. A feedback winding on the transformer provides voltage feedback to the control IC. [3] [4] [5] Counterfeit [6] .000 times per second. allowing it to provide the exact amount of power required with very little power wasted as heat. unlike the bulky transformers used for 60 Hz AC. and the output capacitor smooths it out. the high frequencies allow the charger to use a small transformer. Finally. [2] Since the counterfeit charger is much simpler. The transformer converts this to the desired high-current 5 volts. the blue snubber capacitor absorbs current spikes when the transistor is switched off. the bridge rectifier contains four diodes which convert the AC into DC (at about 170 to 340 volts ). It passes through a fusible resistor. A few components round out the circuit. The principle of a switching power supply is the power is switched on and off tens of thousands of times a second. The switching power supply is the innovationthat allows these chargers to be so compact. This chopped DC is fed into the primary winding of the flyback transformer. unlike the heavy "wall warts" powering older consumer electronics. The input capacitor smooths out this power. the IC power capacitor smooths out this power.The circuit board of a real iPad charger (left) and a counterfeit charger (right). Below this. The 4-pin control IC monitors the charger and uses the switching transistor to turn the high-voltage DC on and off 41. The output diode produces DC. which acts as a safety fuse. Finally. it is easier to understand how it works and I'll explain it first in reference to the picture below. In addition. This winding also powers the IC. The AC power enters through the white wires in the upper left. How the chargers work Both the real and counterfeit chargers use similar flyback switching power supply circuits. On the output side (left). The tiny NTC temperature sensor lets the charger shut down if it overheats. but improves the power quality.) [7] iPad . The AC input is on the lower right. (I removed some of the charger's insulation to make the components visible in this photo. inductor. and two large electrolytic capacitors. This increases the cost. The primary has much more filtering than in the counterfeit charger with a filter coil (common mode choke). the charger has two filter capacitors. and goes through a 2A fuse (in black insulation for safety). The Y capacitors help reduce interference. including a high-quality aluminum polymer capacitor (with the magenta stripe).Inside a counterfeit iPad charger The genuine iPad charger below operates on similar principles. although the circuit is more advanced. The control IC provides advanced control of the charger under varying conditions. things get complicated in the Apple charger. the charger includes additional input filters as well as spark gaps. The latch release circuit lets the charger reset quickly from faults. Starting with the AC input in the upper right. On the other side of the circuit board. [8] [9] [10] [9] [20] iPad .Inside a genuine iPad charger.) The current sense resistor lets the IC monitor the current through the transformer and the line voltage resistors let the IC monitor the input voltage (as well as initially powering-up the IC ). (This IC is much more complex than the control IC in the counterfeit charger. The protection circuit uses the temperature sensor on the other side of the board to shut down if there is an overvoltage or over-temperature problem. The circuit board inside a genuine iPad charger showing the components. The picture below shows one of the surface-mount components (a 0-ohm resistor ) from the iPad charger. using Apple's proprietary system (details). The Y-capacitor filter works with the Y capacitors to filter out noise. [11] Both chargers use resistors to put special voltages on the USB data lines to indicate the charger type. [12] When looking at these circuits up close. while the counterfeit indicates that it is an Apple 1A charger. Note that the real charger has a ground connection. [13] . (This is why iPads say "Charging is not supported with this accessory" with some chargers. it's easy to forget just how small the components are. The output filter circuitry is more complex than in the counterfeit. It is just to the left of Roosevelt's chin on the dime. The secondary side includes some special features for power quality.) Through these resistors the genuine charger indicates that it is an Apple 2A charger. unlike the counterfeit charger which has a plastic pin here. This shows that the counterfeit is really a 5W charger packaged as a 10W charger. or even killyou. or lack thereof Safety probably isn't something you think about when you plug in your charger. Inside the charger is 170 volts or more with very little separating it from your iPad and you.the distance between them along the circuit board. If something goes wrong.A zero-ohm resistor Safety. If you buy a cheap counterfeit charger. You can't see the safety risks from the outside. but in general there should be at least 4mm between high-voltage circuitry and low-voltage circuitry. injure you. Used with permission Creepage and clearance The UL regulations require safe separation between the high voltage and the low voltage.the distance between them through air. [14] iPad . Photo by Anool Mahidharia. I can show you the dangers of the counterfeit. [14] Counterfeit iPhone A Counterfeit iPhone charger that burned up. the charger can burn up (below). The regulations are complex. but it's important. Devices such as chargers have strict safety standards . This is measured by creepage .if you get a charger from a reputable manufacturer. and clearance . but by taking the chargers apart. these safety standards are ignored. (This is a contrast with the rest of the circuit board. The image above shows how the genuine iPad charger's circuit board separates the high voltage (bottom) from the low voltage (top). The happy face on the left marks a slot in the board that separates the low voltage and high voltage.The iPad charger provides safe creepage and clearance distances between the primary high-voltage side (bottom) and secondary low-voltage side (top). Additional reddish-brown insulating tape goes through this slot. The happy face on the right marks an empty region that provides a safety gap between the primary and secondary. which is crammed full of components. The photo below shows how an insulating fin is built into the case and through this slot to protect the USB connector. iPad .6mm provides a comfortable safety margin. and the whole high-voltage section is wrapped in yellow insulating tape.) This gap of 5. The result is multiple layers of protection. Dime and banana are for scale.6 mm separation between low and high voltage. But obviously the electrical power needs to get through somehow. which is a hint of better quality and more power capacity.) 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 creepage distance. If you use the charger in a humid bathroom and a drop of water condenses across the 0. then zap! Counterfeit Dangerous creepage in a counterfeit iPad charger. (The ruler on the right indicates millimeters. Disassembling the transformers shows that this is the case.The iPad charger case has a plastic fin that slides around the USB port to provide extra insulation. Safety in the transformer For safety. The flyback transformer accomplishes this task by using magnetic fields to transfer the power without a dangerous direct connection. [15] iPad Counterfeit The flyback transformers from an iPad charger (left) and a counterfeit charger (right). But overall. The sad face on the right shows where a lowvoltage trace is nearly touching the high-voltage trace below. this board is unsafe. the high-voltage and low-voltage sides of the charger must be electrically isolated. it is tempting to take safety and quality short cuts here.only 0. The genuine transformer (left) is considerably larger than the counterfeit (right). . The creepage distance on the counterfeit charger board below is scary . Because the transformer is a large and relatively expensive component.6 mm gap. The triple-insulated wire is an important safety feature that keeps the high voltage out even if there is a flaw in the insulating tape and in the wire's insulation. The wires look similar at first glance. then zap! iPad Counterfeit The real charger provides much more power with much less noise . The pictures below show the transformers after removing primary windings and insulating tape. but the the genuine charger (left) has triple-insulated wire while the counterfeit (right) is uninsulated except for a thin varnish. revealing the secondary winding. and the counterfeit charger fails here.The key safety requirement of the transformer is to separate the high-voltage windings from the low-voltage secondary winding. the only thing separating the secondary winding from high voltage is the insulating tape. If there is a flaw in the tape or the wires shift too far. Also note the additional black and white insulation on the wires where they leave the transformer. In the counterfeit charger. .9 watts. not 10W. The real charger has a stable yellow thin line. First.) The other thing to note is the line for the Apple charger is smooth and thin. so the counterfeit charger is actually twice as bad as it appears here. The following voltage-vs-current graphs show the performance of the iPad charger (left) and counterfeit charger (right) under increasing load. Second. while the counterfeit charger's output has large voltage spikes. due to 120 Hz ripple appearing in the output voltage.) The bottom of the counterfeit charger's yellow line is wavy. see my article testing a dozen chargers. The yellow line shows the voltage.Lab measurements of the output from the chargers shows a couple problems with the counterfeit. while the counterfeit charger's line is all over the place. (I had to change the scale to get the output to fit on the screen. (For details on these graphs. iPad Counterfeit The next pair of graphs shows the power quality.9W. the counterfeit turns out to provide at most 5. The line for the real charger goes much farther to the right. This indicates that the power provided by the counterfeit charger is noisy and low quality. showing that the real charger provides much more current. the real charger provides a maximum of 10. The consequence is the real charger will charge your iPad almost twice as fast.1 watts. the output voltage is extremely noisy and full of spikes. By my measurements. while the counterfeit charger provides only 5. this is probably the cause. The biggest impact it has is on touchscreen performance. with a large spike at the switching frequency. [16] Inside the real charger's transformer There's more inside the transformer that you'd expect. This shows that the counterfeit charger's power is worse across the frequency spectrum. If your screen malfunctions when plugged into a charger. iPad . and higher is exponentially worse. You might wonder if the power quality actually matters. The interference from bad power supplies is known to cause the touchscreen to behave erratically. This section does a full teardown of the transformer from the genuine charger.iPad Counterfeit The orange line shows the frequency spectrum of the output: lower is better. The counterfeit spectrum is much higher in general. iPad The first photo above shows that underneath the the first layer of yellow insulating tape. a layer of copper foil is attached to the transformer's ferrite core to ground it. removing the ferrite core and more insulation reveals the double-stranded primary winding. The highvoltage input is fed into this winding. Next. iPad . ) After removing more insulating tape. iPad . The next layer of insulation (right) contains copper foil. the secondary winding of the transformer is visible. which provides feedback and power to the control IC. (In the photo. this winding has been removed and is surrounding the transformer. This helps reduce interference. As discussed in the safety section.iPad Underneath the primary winding and more insulating tape is the triple-stranded bias winding. the secondary winding has triple-insulated wires and extra insulation where the wires leave the transformer. The iPhone charger (below) uses two circuit boards that combine to form a one inch cube. The iPhone and iPad chargers are both flyback switching power supplies. the secondary winding is plain copper wire. but the feedback mechanisms are very different. [17] iPhone . but results in a better transformer due to better coupling of the magnetic fields.) It simply has the bias winding (pic). separated by insulating tape. In my detailed iPhone charger teardown I looked at the internals of the iPhone charger. In comparison.Finally. secondary winding (pic). and primary winding (pic) . the innermost layer of the iPad charger flyback transformer is the second half of the primary winding (above). click through to see them. Overall. How does the iPad charger compare to the iPhone charger? The iPad charger is considerably larger than the iPhone charger and provides twice the power. The counterfeit also doesn't use the more expensive split. multi-stranded windings that the genuine charger uses. which is a significant safety flaw. the counterfeit saves cost by omitting the copper foil layers. As discussed earlier. Unlike the genuine transformer. which is impressive engineering. (I haven't included the pictures for reasons of space. the transformer of the counterfeit charger is much lower quality. mainly because of the harder engineering challenge of cramming everything into a much smaller space. not triple-insulated wire. Splitting the primary winding into two layers is more expensive. I like the iPhone charger more than the iPad charger from a design standpoint. You should definitely stay away from the cheap counterfeit chargers. but is a high quality product. I drew up a schematic of the charger. You can see from the schematics that the genuine charger has a much more complex circuit than the counterfeit. The counterfeit charger is almost identical to the schematic in the DB02A controller datasheet. as they are low quality and . but for the iPad chargers I didn't need to do this.) [18] iPad Counterfeit Is the Apple charger worth the price? Apple's charger is expensive compared to other chargers. The genuine iPad charger is almost identical to the reference design schematic provided by iWatt. (Click the thumbnails below to get to the datasheets.Schematics In my iPhone charger teardown. The companies state that they are entirely independent. the chip is for 500mA-1000mA chargers. I've bought several for testing. But I'll refer to the 5V output as low voltage for convenience.it's amazing that a charger can be manufactured and sold for such a low price (if you don't care about safety and quality). a different company. though (statement. [19] In any case. It's a puzzle why some companies use TO-94 to describe 4-pin inline packages. the magnetic field collapses. [2] The chargers uses a flyback design. which explains why the counterfeit charger only produces 5 watts. [4] The counterfeit charger uses a DB02A controller IC. TO-94 is a bolt-like package for large SCRs. Flyback power supplies are very common for low-wattage power supplies. Thus. Foxconn is the company with controversy over employee treatment. while Foxlink is smaller.) According to the datasheet (Chinese). where the transformer operates "backwards" from how you might expect. and they have always been genuine. When a voltage pulse is sent into the transformer. and Flextronics (Singapore) are all manufacturers for Apple with confusingly similar names. with some better than Apple. instead of the 10 watts an iPad charger is supposed to produce. but looking at the price of similar chargers from other manufacturers and the cost of components. there are big differences inside the case. the output diode blocks the output so there is no output . . The transformer core has a tiny air gap to help store this field. since the diode charges the capacitor to the peak of the AC signal. I think Apple has a huge profit margin even at $19. you mostly get what you pay for. Overall.35 (about 6 cents). According to standards. the iPad charger is an impressive piece of engineering with a lot of interesting circuitry inside.dangerous. This isn't enough to be officially high voltage but I'll call it high voltage for convenience. This controller is very inexpensive.available for ¥ 0. Foxconn (Taiwan). This controller only has four pins and is in a TO-94 (SIP-4) package. The counterfeit charger is also impressive in its own way . Non-Apple name brand chargers are generally good quality according to mytests. (According to the official JEDEC standard. If you want to get an Apple charger without the high price. the input of 100 to 240 volts AC is converted to a DC voltage of 145 to 345 volts internally.instead a magnetic field builds up in the transformer. The DC voltage is approximately sqrt(2) times the AC voltage. even if you can't tell from the outside. I wrote earlier about Apple's huge profit margins on chargers. Apple has since dropped their charger prices from $29 to $19. When the voltage input stops. Foxlink annual report). Interestingly. [3] You might wonder why the DC voltage inside the power supply is so much higher than the line voltage. the best way I've found is to buy a used one on eBay from a US source. transferring power to the output winding. which is more reasonable. Foxconn and Flextronics are the world's #1 and #3 largest electronics manufacturing companies according to the MMI top 50 for 2013. the chairmen of both companies are brothers and the companies do a lot of business with each other. this charger is made by Foxlink. anything under 50 volts AC or 120 V dc is considered extra-low voltage and is considered safe under normal conditions. Notes and references [1] Foxlink (Taiwan). The output diode is a SR260 Schottky barrier rectifier. it appears to be a Chinese design with datasheets only in Chinese. One interesting feature is the many white pads around the outside of the die.I couldn't find any US chips similar to this chip. Since the chip only has four pins. . Three of the four wires connect in the lower left. This transistor is a version of Motorola's MJE 13003 switchmode transistor which was introduced in 1976 (MJE indicates power device in a plastic package). [6] In the counterfeit charger. The die has the label "N7113 802" at the right. which are used to blow fuses to trim various resistances in the chip. see Passive Lossless Snubbers for High Frequency PWM Conversion and Switchmode Power Supply Reference Manual. it creates a voltage spike. The bridge rectifier is a B6M (datasheet).but I cracked it open with Vise-Grips and it turns out to be a fairly complex chip. manufactured by "Fine Made" Shenzhen Fuman Electronics. [5] When a diode or transistor switches. and the fourth in the lower right. which can be controlled by a special snubber or clamp circuit. For a lot of information on snubbers and clamps. I expected it to be a trivial Ringing Choke Converter (RCC) circuit with just a couple transistors inside the chip . which is about 1 mm across. the switching transistor is a ALJ 13003 NPN power transistor (datasheet). apparently made by Shenzhen LongJing Microelectronics Co. I wasn't expecting to see this level of quality and sophistication. even after a lot of searching. I took a picture through a microscope of the IC die. I don't know what this indicates. Die photo of the DB02A SMPS controller chip used in the counterfeit charger. (See the schematic for details. the input capacitors may store power for many seconds.pins. with different behavior under no load. by the way. where similar spark gaps are designed to discharge accumulated charge for a 3KV lightning surge test. If there is a fault. It controls the switching frequency and length of time the power is switched on.this circuit has a much smaller capacitor. Different types of Apple chargers use resistances to put different voltages on the USB D+ and D. But if the control IC isn't running. the control IC is powered by the transformer's feedback winding. This chip sells for about 30 cents. (You may have seen LEDs remain illuminated for several seconds after unplugging devices.) This seems like overengineering to me. [12] Apple uses a proprietary technique for the charger to indicate to the device what kind of charger it is. the 1691. For more information on X and Y capacitors. after unplugging a charger. For details on USB charging protocols. and high load. while the counterfeit has a plastic pin. unfortunately the zero-ohm resistor is a bit more than 0 ohms. [10] The genuine charger uses a complex control chip manufactured by iWatt. It does this by providing a separate diode bridge for the charger's power . However. In normal use. the US plug doesn't use the ground connection. Ironically. so this is one safety issue that doesn't make any difference in practice. the transformer won't work. This chip monitors the input line voltage. but one example of it is an Infineon SMPS design. the current through the transformer. and is specially designed to avoid any safety hazard.if you feel a tingle from your charger. This indicates that the charger is covered by the safety standard UL . but I expect Apple gets a better price.) The latch release circuit ensures that the charger will reset properly even if you plug it back in quickly. I couldn't find a lot of information on this sort of spark gap. and the voltage feedback from the transformer. [8] The iPad has two spark gaps next to inductor L1 (the input AC common mode choke). A detailed presentation on the iW1691 is here. It does. [11] The real charger has a metal ground pin that connects to the power plug. adding extra circuitry for this rare case. [9] The Apple charger includes a "latch release circuit". see my earlier references. [14] The outside of the charger has the slightly mysterious text: "For use with information technology equipment". low load. however. The solution is a startup power path where the control IC gets enough power from the AC input to start up. This capacitor helps reduce EMI interference. so it will power off quickly. While this resistor may seem pointless. pass a tiny amount of electricity . leading to a chicken-and-egg situation. This is one difference between the chargers that is visible externally if you slide the power plug off the charger. as well as constant monitoring for faults.[7] The iPad charger uses special Y-capacitors to bridge the high-voltage and low-voltage sides of the charger. and then switches to the transformer. it allows the manufacturers to substitute a resistor later if different transistors require it. see Kemet's presentation and Designing low leakage current power supplies. [13] While it would be nice to find superconductors inside the charger. these capacitors are probably the cause. the control IC will shut down the charger until power is removed. the iPad charger's primary diodes (F6w) are 1. see i-Spec Circuit Separation and some of my earlier references. This probably means iWatt did most of the design work for Apple. . and a R/C filter attached to the Y-capacitor on the secondary side. Optoisolators use a light signal to provide feedback between the circuits in an iPhone charger. which should approximately match the output voltage. then design adds only one cent to the cost per charger. as well as a (zener?) diode in the switching transistor drive circuit. [16] For an explanation of why the noisy output from cheap chargers messes up touchscreens. The charger has RC snubbers the input bridge rectifier (a rare feature also in the iPhone charger). The bridge rectifier is a bridge: MB10S CD 0. First. which specifies the various isolation distances required. but are not used in the iPad charger.60950-1. The component in the protection circuit that looks like a transistor is a BAV70 dual high-speed switching diode (datasheet). The article blames touchscreen problems on aftermarket low cost chargers. The output diode is a SBR10U45SP5 10A super barrier rectifier (datasheet). [20] For those interested in the components. The Y capacitors are 220pF 250V. which is very difficult when AC noise is present. which is most of the design work. iWatt's designers deserve credit for the complex control chip and the reference design. Comparing the actual charger with the reference design shows a few filtering improvements. The iPad charger uses two Y-capacitors instead of one. The article discusses how capacitive touchscreen ICs need to sense pico-Coulombs of charge. Second. The switching transistor is an Infineon SPA04N60C Cool MOS® 650V power transistor (datasheet). [17] The biggest difference between the iPhone charger and the iPad charger is the feedback used to regulate the voltage. the iPad control IC looks at the voltage in the feedback winding. The iPad charger avoids these components by using primary-side regulation. The charger has an extra diode on the secondary for filtering. The charger connects line ground to secondary ground through a resistor. The iPhone charger measures the output voltage with a TL431 chip and sends a feedback signal to the control IC via an optoisolator. [12] [19] Some people think that I'm ignoring Apple's cost of designing chargers when figuring their large profit margin. The reference design doesn't show the USB data resistors . and not to short out if they fail. [18] I noticed only a few significant differences between the iPad charger and iWatt's published 1691 charger reference design. if you spend $2 million on design and manufacture 200 million chargers. For a brief overview of isolation distances.5A 60V Schottky Barrier Diodes (datasheet). The "T3" diodes are fast switching diodes (datasheet).5A bridge rectifier with high surge capacity (datasheet). Ycapacitors can also bridge the primary and secondary side because they are designed not to pass dangerous currents. [15] Only a few special components can safely bridge the gap between the high voltage side of the charger and the low voltage side. see Noise Wars: Projected Capacitance Strikes Back. The most obvious is the transformer. Instead of measuring the actual output voltage. 3V X-CON ULRaluminum polymer capacitor (which is more expensive than a regular electrolytic. and a 820 µF 6. The output capacitors are a Koshin KLH 820µF 6.The input capacitors are Samxon 10µFand 4. but filters better because of its lower ESR).7µF 400v electrolytics.3V aluminum electrolytic. .