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Is mixing charger and computer safe

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Is it really safe to plug the power end of the Y-cable into a charger and the other into your host computer? (As described in http://jevois.org/doc/UserConnect.html). It seems to me that there could be a difference in potential between the two?

I wasn't able to find a good answer online. The best i could find is https://superuser.com/a/1022965
asked May 26, 2019 in Hardware Questions by toktuff (200 points)

1 Answer

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Best answer
USB ports usually have a power switch IC to protect them, for example http://www.ti.com/lit/ds/symlink/tps2549.pdf

Indeed, without this, one could fry a computer's motherboard just by inserting a bad USB device, shorting the port with a metallic object, etc so it is in the interest of computer manufacturers to always include the protection IC so that they do not have to deal with returned computers with fried ports.

Y cables have been around for a long time because of external hard drives and DVD writers. From the post you suggested, I would say 1) and 2) are taken care of by the protection chip. Indeed there is a risk of 3) in principle which you can resolve by first connecting both grounds together, which usually is what happens first as you insert the USB plugs into the receptacles.
answered May 29, 2019 by JeVois (46,580 points)
selected Jun 17, 2019 by toktuff