I’m not sure if this is familiar to you – but it certainly is to me. Along the same vein of cheap eBay goods, and chargers, this is another one of those “cheap” Chinese specials. This is a cheap USB charger. I bought it off a friend a long time ago, and it seems to work just fine, although it gets a bit hot and noisy, but a recent news article of Ma Ailun’s death while using an iPhone, which appears to be linked to a counterfeit charger gave me pause to take this one apart and see what’s inside.
But before I do that, let me refer you to Ken Shirriff’s blog – he has made many very detailed, well referenced postings in regards to counterfeit chargers and has compared the power quality of several others. Also interesting, was his take on the historic development of switchmode power supplies, also worth a read. It was extremely fascinating to see what’s inside a proper genuine quality Apple square US prong charger – I’ve had a counterfeit myself which exploded in flames. Many kudos to Ken! I have learnt much from his postings, which, seem to have seen a surge in views with this latest news.
The Charger I Have
It’s pretty non-descript, although there was a label stating 5.2v at 500mA if I remember correctly. It’s a charger, what do you expect? The one thing I did note was that my friend had three, but one had “burnt out” on him. That’s a sign of just how cheap this is.
Inside the cheap charger, you could see it as utter rubbish, or as being half decent. The good – well, there appears to be an opto-isolator of the secondary to the primary – a good “safety feature”. The bad? Well everything else. There doesn’t appear to be much filtering of the secondary – I can’t spot any hefty inductors. I do spot a lot of “burnt” coloured resistors which indicate they’re being run at or near capacity. A lot of diodes were saved at the input stage – we’ve gone from a layout for full-bridge rectification to just half-wave rectification, meaning lumpy power (and a possibly unhappy power grid if enough of these were in use). There’s no input fuse – and no transient filters. If a surge was hefty enough, it could probably fry the secondary too …
The underside does have a clue to the PCB labelled LDT 03A-1. It has a clear separation between primary and secondary – which then leaves the insulation of the transformer in question, but that’s still better than the other shocking designs.
The one qualm? Well, it gets hot supplying 500mA, and can’t really do more than that. But it also causes touchscreen malfunctions. Thanks to Ken’s blog, and his link to this whitepaper by Cypress, I now understand why. It’s noise. Lots of it.
So, if you dare to risk your expensive devices (and possibly, your life) with cheap chargers, and your touch-screen is acting up – now you know why!