Mobile charger has become one of the most popular accessories/consumables for smart-phone (thanks to Apple’s non-removable battery design). Being a heavy mobile internet user, I have accumulated several mobile chargers, ranging from top-of-the-line Energizer “Energi To Go”series, to homebrew single 18650 lithium battery adaptor. All of them have proved to charge mobile phone well. But are they good enough to power testing circuits for lab use? I cannot have good confidence until I tear them apart and measure their performances.Before going further, let’s imaging what are the essential circuitries for a mobile charger.
- First thing of course is the battery. For modern chargers it is usually a 3.6/3.7V lithium-ion or lithium-polymer type. The capacity of the battery directly determines the price of the charger. Overrating capacity is not unusual. As my personal guideline, for a charger weights about the same of an iPhone (120g), the capacity should be around 5000-6000mAH. So if you encounter a charger weights less but rated as much as 10,000mAH, avoid it at all costs. It is not because of the capacity, but the manufacture’s integrity and the confidence over other parts of the charger.
- Since the battery is 3.6/3.7V and USB specification is 5V, there should be a DC-DC boost converter inside the charger. DC-DC circuit introduces noise and ripple. Although noise and ripple are not of concern for charging mobile phones, they are very important for lab use.
- The battery needs to be charged. Lithium battery usually charges at 4.2V and it must be a CC/CV charging process. So there will be a charging circuit.
- Using lithium batteries also implies the need of protection circuit to prevent over charging or discharging.
Too much for the theory. Here comes the victim of today’s tear down.
The most useful tool to test battery is a constant current dummy load. Unfortunately I do not have one. So I’ll use a high power LED light as load. The light draws 414mA from USB port. It should be close to the charging current of mobile phones.
Charger “A”) This is one of the most popular chargers in the market today. The label says “Power Bank for iPad/iPhone”, with out brand or manufacture whatsoever. Here in Singapore it costs S$20 online. But in China you can get it as low as RMB29. The weight is 120g and capacity rating is 5000mAH, which does not seems to be overrated.
The first test is to measure its output ripple voltage under load. Just a side note: to measure ripple voltage (usually at several mV to several hundred mV), the ground link of your oscilloscope test lead will function like an antenna that picks up higher EMI noise than the actual ripple. So you must take out the ground alligator clip and use the spring header instead, as the photo below:
As a low cost charger I did not expect too much quality from the charger. The result confirms it: the ripple is as high as 768mV peak-to-peak. Base ripple frequency is about 100kHz but mixed with higher frequency spikes. I don’t think it is anything good for lab use. Even use this to charge mobile phone makes me feel uncomfortable.
So what’s inside this charger? Let’s have a look inside:
As I’ve expected, it contains a lipo battery without marking 🙁
Here is the DC-DC boost converter. The chip is marked “PCN TSA2Q”, corresponding part number PAM2421, by “Power Analog Microelectronics Inc”, datasheet here. The rated efficiency is about 87% for 3.6-5V boost at 400mA load. Interestingly my measurement didn’t show the rated 520kHz switching frequency. The datasheet does not mention anything about ripple, seems the manufacture is purposely trying to avoid the topic.
The charging circuit is based on “AP5056” chip. Googling 5056 resolves several Chinese webpage, like this and this. It seems the chip does implement CC/CV charging mode and automatic charging termination.
Chip “DW01” and the two MOSFET 8205A are the lithium battery protection circuit. DW01 datasheet can be found here.
There is a 14-pin chip in the upper side of the PCB. Interestingly it is not a chip with markings being scratched off (like many other Chinese products). This chip is manufactured without marking! My guess is that this is a micro controller in charge of blinking LED lights, as the charger actually has a 3-segment LED to indicate battery level. But why is it without marking? To prevent being copied?
Verdict: This is a typical Chinese ShanZhai(山寨) product. I’m not sure if it is copied from somewhere else or the engineer roll out their own. The parts used in the charger is sub-prime, hence it is low cost. With huge ripple voltage I’ll not take it for lab use. It is potentially good to light some LED lights but use it to charge expensive mobile device is the last thing I’ll do.
Charger “B”) Charger “B” is a typical iPhone charging case. I got it from a friend who “upgraded” his iPhone to a Samsung Glaxy Note. It weights 70 gram and rated 1900mAH, seems realistic for this type of charger. The battery is pretty weak when I received it. My intention is to take out the PCB and see if it can be used for other purposes. So I measure ripple voltage:
Ripple is 212mV peak-to-peak. Compare with Charger “A” this waveform is much clearer. DC-DC switching frequency is about 416kHz.
Taking the charger apart and check the battery, again we found an unlabeled lipo cell 🙁
Surrounding the bulky inductor should be DC-DC converter circuit.
The converter chip is marked “AA2C”. But Google cannot find its actual part number. “AA2C” could just be the manufacture’s internal code. Anyway giving its ripple voltage I do not believe it is anything worth investigating.
The charging circuit is based on the chip marked “2YL6”. Again it is some internal code. But this time Google resolves some post at Yahoo groups which leads to this datasheet. The actual part number is BL4045, by Shanghai Belling Co. Ltd. It does CC/CV charging and automatic termination. Everything looks fine here.
The protection is using the same chip “DW01” as we seen in charger “A”. Only difference here is that charger “B” uses one 8205A MOSFET instead of two in Charger “A”. Since 8205A is dual MOSFET, why charger “A” needs two of them?
Charger “B” also has a MCU to blink the LEDs. This time it is a Haier HR6P61P2S4L. Before today I thought Haier only makes washing machines and fridges 🙁 HR6P61 is a 8-bit, 8Mhz, Harvard architecture micro controller. The word “Harvard” sounds familiar to me … and no surprise Microchip is using the same architecture, and no no surprise Microchip has filed lawsuit against Haier for copying there microcode. I have no authority to give judgement here, but this kind of thing is not uncommon, shame! (after thoughts: maybe it explains why charger A has the chip blanked?)
Verdict: The build quality of this charger is decent. It functions well as a charger, but to use this as a lab power supply is a bit shaky. Use it for LED lamps perhaps.
Charger “C”) This charger is special. The model is “ML-102”, originates from a design by members in a Chinese forum. I paid RMB 32 from taobao.com. This charger does not comes with battery, you have to supply your own 18650 lithium battery. The advantage of using external battery is that the capacity will never be over rated. How is the ripple? This is the result:
73.6mV! Or 1.5% of full 5V range. Not too bad at all. Ripple frequency about 500kHz with some high frequency spikes.
Here is the DC-DC converter, based on “PT1301”, datasheet here. Rate efficiency is 88% flat at loads from 50-300mA, which is hard to believe. The maximum output current at 5V is 300mA, so do not expect this charger to charge quickly.
Protection circuit is “VGP4” and “8205”. Apparently 8205 is the MOSFET. VGP4 is? Google has no idea, let alone me.
Charging is supported by two TP4057 and one Fairchild MOSFET FDS4953 at 1A charging current. It takes about 5 hours to fully charge my Panasonic NCR18650A 3100mAH cell. On the discharge side, it is enough to fully charge iPhone twice.
Verdict: The design of ML-102 is unique. It can be used as mobile charger or directly charge 18650 cells. However 18650 battery is not available on the consumer market (at least here in Singapore), so the charger is more suitable for the professionals. Overall the charger performs pretty well. May fat hop was that the schematic for this charger is open. But as a Chinese design I would rather not expect too much. As the output ripple voltage is considerably low, this charger is good for lab use to power digital circuits. But for analog circuits I would incorporate a linear LDO in series.
Charger “D”) This is the first mobile charger I bought 3 years ago, long before the market is saturated with cheapo chargers. As it is from the famous “Energizer” brand I’m having good faith in it. And in fact after 3 years of extensive use it still stands strong, better than many laptop batteries.
The charger weights about 175g, rated at 4000mAH, I’d rather think it is under rated. The model number is “XP4001”, manufactured by “TennRich Electronics (Shen Zhen) Co., Ltd.”. At least the manufacture dare to put their name on it!
We check the ripple first. And Wah! 38mV peak-to-peak, and this 38mV is only contributed by spikes.
I was a bit hesitated to pry the case open, but I really want to see what’s inside. And in fact during the process I broke two plastic latches 🙁 Not surprisingly this time the battery has a label, although the label gives no information about the actual capacity. There is a “3M” double side tape on top but only used as “single side” tape. It would be harder for me to tear it apart if the top side also sticks to the case.
Here is the DC-DC part. Again a mysterious chip “L3K3”.
Interestingly just beside the DC-DC converter there is another inductor. Tracing the circuit, I realize it is actually an LC Π filter sits in-between the DC-DC converter and output socket. It explains why the ripple is so low in this charger. They really spare no effort to keep the waveform clean.
The XP4001 charging circuit is based on “VA720?” IC, manufactured by “VIMicro”, date code looks like 51 week of 2007. I have looked into VIMicro website but unable to find any information.
The battery protection circuit is similar to all the others, using “312F” chip. No further information available.
Verdict: The XP4001 charger is among the best in terms of life span, output stability and build quality. Although expensive (S$99 three years ago), it really worth every cents. The output ripple is good enough for most lab use, adding some more filtering will make it even better. However this charger has a annoying feature that it disconnects its power if the load is too low. So I have to frequently press the button on the unit to keep it “awake”.
Conclusion: The electronics market is full of gimmicks. While consumers focuses more on appearance and advertised features, the internal quality of the product is often neglected. In the event that one cannot tear the product apart and check the internals, trusting the brand name seems to be the last insurance. And my advise to those who are constantly looking for bang-for-buck deals: never ever trust a Chinese product without looking inside of it.