General > General Technical Chat
Measuring max output current of a USB port.
pcprogrammer:
--- Quote from: wraper on October 21, 2022, 06:57:23 pm ---You don't need any scope or other nonsense.
--- End quote ---
No one mentioned using a scope for measuring the current :)
balnazzar just wanted to verify that his new Owon USB scope is getting enough current when connected to a single port. And I told him that he can use his new scope to check on things when building his own scope, you know, what is being discussed here: https://www.eevblog.com/forum/testgear/building-my-own-scope/
:-DD :-DD
mariush:
Majority of motherboards will have resettable fuses on the USB ports ... for example a 2.4A fuse for each pair of type A ports.
By default, USB 3 is supposed to give up to 0.9A, so this way you could one of the two ports give 2A of current to a device (like an external mechanical drive for example) or some other gadget that needs more power, without tripping the fuse.
wraper:
--- Quote from: mariush on October 21, 2022, 08:23:21 pm ---Majority of motherboards will have resettable fuses on the USB ports ... for example a 2.4A fuse for each pair of type A ports.
By default, USB 3 is supposed to give up to 0.9A, so this way you could one of the two ports give 2A of current to a device (like an external mechanical drive for example) or some other gadget that needs more power, without tripping the fuse.
--- End quote ---
Barely any if any at all modern motherboards use resettable fuses for that. They use MOSFET based power switch/current protection ICs. With PTC fuses it's unlikely you can keep VBUS voltage in spec while having meaningful protection triggering current.
Nominal Animal:
Personally, I'd connect the Owon VDS1022i to a powered USB hub, and connect the hub to my computer, making sure the hub is powered using an isolated wall wart and can deliver at least the 2A specified. Since it is an 'i' model, it's supposed to have an isolated USB interface.
magic:
If the USB interface is isolated but there is ground and 5V connection with the computer, it kinda defeats half of the purpose of isolation.
If something bad enough happens to the scope, like grounding clip connected to a "hot ground" ::), your computer goes :-BROKE
The scope should be fixed in the first place :-/O
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