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Reverse engineering of a chinese Li-Ion charger

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thexeno:
Hi,

Already the title should raise a red flag.
Nevertheless, I've had a chinese power torch:



which seems the same described by DiodeGoneWild here.

He has a PROTECTED Li-Ion cell and a super dodgy power supply, in which when does not kill, probably will work (for some times) in charging the cell.
Conversely, mine did have this cell:



For which the P/N corresponds to the italian website stating does NOT have protection. So I knew it was dangerous and the charger most probably is the same quality of the one in the video, but I wanted to still check it out - but I am not sure if I reverse engineer it correctly, since the feedback circuit seems a bit cryptic. Also, I did not have clue on the winding polarity of the transformer.

To begin, this is the PCB, in which already the isolation clearance is broken:



And the front is this:



Now, the reverse engineered schematic looks like this one:



Getting to the first question, is this correct? If so, how does work the feedback? Does it use an 1N4148 with the 6.2V zener for the BJT feedback?

Second question: how is that possible that such dangerous crap is freely sold here in Europe? Because it was in a perfectly legal shop, was not bought from a shady eBay distributor.

EDIT: fixed the pics :)

magic:
Looks like the ubiquitous "ringing choke converter". There is obviously no secondary voltage feedback. The zener may be involved in regulation using auxiliary winding voltage sensing.


--- Quote from: thexeno on December 26, 2019, 05:02:15 pm ---Second question: how is that possible that such dangerous crap is freely sold here in Europe? Because it was in a perfectly legal shop, was not bought from a shady eBay distributor.

--- End quote ---
Because nobody controls it.
Does the charger have the CE mark on it? If not, the shop sells it illegally. If yes, the original manufacturer applied it fraudulently or meant "China Export" by it ;)

edit
https://www.electroschematics.com/diy-rcc-smps-circuits/

Without reading, my guess is that during secondary conduction time the 1N4148 discharges the electrolytic to negative voltage proportional to the secondary voltage and if this is too low, the zener later steals base current from the transistor.

MarkF:







SiliconWizard:
Nice. No constant current phase. A voltage output of 4.2V +/-0.5V (!!!  :-DD) (and I even doubt this figure). What could go wrong really? :-DD

Dear lord.

magic:
Those circuits can be current limited, but on the primary. I suppose that secondary current is roughly proportional to input voltage ;)

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