[music_man]

i see that a usb hub will power itself off the pc without it's psu. i was wondering if when the psu is connected it breaks the connection from the pc. or if it is just boosting the pc's power and still letting the pc's power through to your devices? if you want to use it for a lps do you have to cut the +5v somewhere or does the hub automatically do that? thanks.

 

[pinnahertz]

Back-feeding 5V into a PC's USB connector would be a really bad idea, so I'd guess a good hub would perform some sort of switching or at very least have a couple of steering diodes.  

 

[music_man]

thank you. i would figure most have to. for the reason you said. however the one i am playing with operates on 12v. i can plainly see in it's topology that it disconnects it. i would think all have to though. or your motherboard would be fried. most work unpowered but that does not mean they do not break the connection when the psu is applied. that would plain and simple kill the motherboard. unless some just have forward direction only. that would work too i guess.

 

[music_man]

this is very strange. startech claims all their hubs break the vbus when the psu is present. one i can run it with no vbus present. the other requires vbus to operate at all. even with the psu. i do not think a hub has to handshake like a dac. i am weary that hub is letting vbus through on to the dac. however this hub is 12v. i do not understand why the hub would need the pc's vbus to operate at all while on psu. this hub has a very high quality chipset so i am interested in it. i just do not understand why there is no data without vbus. how can i tell if it is letting the dac see the pc's vbus?