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USB power supply puts 220 Mains power out on USB jack

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Re: USB power supply puts 220 Mains power out on USB jack

#5

Post by yoodenvranx »

aembleton wrote: post #4

Big Clive, who makes these videos does some brilliant tear-downs. I recommend watching his other videos.

Big Clive is _the_ channel for teardowns of everyday electronic stuff. I am actually not that interested in this kind of stuff but somehow I still watch most of his videos.

If you are into more... entertaining teardowns you should have a look at AvE. Even if you don't like it you will still learn some useful canadian terms ;) (edit: just to make it clear, AvE is actually very knowledgable. His "boltr" teardown series of electronic power tools is most likely the most thorough you will find on the internet)

My third goto channel for electronic stuff is EEVBlog who also does amazing stuff. If you are going to watch one teardown today then please watch his rather famous video about the worlds worst tablet computer: https://www.youtube.com/watch?v=2o8MDCIlOEk

Re: USB power supply puts 220 Mains power out on USB jack

#6

Post by aembleton »

yoodenvranx wrote: post #5
aembleton wrote: post #4

Big Clive, who makes these videos does some brilliant tear-downs. I recommend watching his other videos.

Big Clive is _the_ channel for teardowns of everyday electronic stuff. I am actually not that interested in this kind of stuff but somehow I still watch most of his videos. If you are into more... entertaining teardowns you should have a look at AvE. Even if you don't like it you will still learn some useful canadian terms ;) (edit: just to make it clear, AvE is actually very knowledgable. His "boltr" teardown series…

Thanks, I'd not seen that tablet computer before. Incredible!

Re: USB power supply puts 220 Mains power out on USB jack

#8

Post by sitharus »

0xffff2 wrote: post #7

Can someone explain why the transformer is on the DC side of the circuit in the diagram he draws at the beginning of the video?

This is a switch mode power supply. In order to use a smaller transformer it uses very high frequency AC rather than 50/60Hz mains frequency.

In order to do this it rectifies the mains input to high voltage DC (330/220Vish, depending on the mains voltage) then using a power transistor rapidly switches this on and off at around 1-10kHz. Then the transformer outputs low voltage AC which is re-rectified and filtered to produce low voltage DC.

The switch mode chip monitors the output voltage and modulates the switching frequency to maintain a constant output voltage.

If you look closely at the board (and he talks about this in the video) there's a separation between the high and low voltage sides. Only the transformer and certain specialized components should cross this (Y-class capacitor and optoisolators). Cheap power supplies often miss this out which could allow a small bit of loose solder being able to send mains voltage to the output. Look at other videos by Big Clive to see the horrors.

The high voltage side is a bit of a misnomer. It's really just the non-isolated side - the chip runs on 5v or similar, but it's not completely separated from the high voltage DC so isn't safe for human contact.

Re: USB power supply puts 220 Mains power out on USB jack

#10

Post by yoodenvranx »

voltagex_ wrote: post #9

How do I know what I'm buying is safe? I've sworn by the Nexus chargers in their various incarnations and http://www.amazon.com/Charge-Charging-Station-Micro-USB-Sams... (I have a Tronsmart and an Aukey vertsion)

I play Ingress a lot (a GPS based mobile game where you run around a lot in the real world so most players use external batteries) and at least 60-70% of the whole community uses Anker products. I personally know at a dozen people who use Anker wall plugs and all of them (including me, 1 wallplug and 2 battery packs) are very happy.
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