Re: flashing usb sticks?

On 3/25/2022 5:46 AM, wasbit wrote:
> "VanguardLH" <[email protected]> wrote in message news:[email protected]...
>>
>> snip <
>>
>> I have an unpowered USB hub (no walmart needed nor having to store) in
>> my laptop's tote bag.  That lets me plug in a keyboard, mouse, and more
>> low-powered USB devices, and more than what the single USB port on the
>> laptop would allow.  At home, I added a powered USB hub when I ran out
>> of USB port since the addition of the A/C adapter wasn't a problem with
>> a desktop PC.
> 
> Of further note is that a USB2 hub can provide enough power to run an external HDD without the use of a 'Y' lead if it's plugged into a USB3 port.
> 

A lack of standards, and the usage of "App Notes" for reference,
makes this topic complicated. For example, I just viewed a so-called
"electrical engineering" thread on a web site, and just above every
answer was wrong.

The best evidence of practices, is to open the equipment and look.
Unfortunately.

There is a difference between desktops and laptops/tablets, because
they represent different thermal environments. Where the current flow
controls are located in a laptop, can have no cooling. And if the
method used was thermal, the results would be "all over the place".
There are methods that are "mostly not thermal", which are used
in laptops or tablets.

Southbridge chips do not measure current. Instead, they have
a logic input #OC that when sent an active-low signal, indicates
that an external device or circuit, has uncovered a problem. This allows
software to put a toast on the screen indicating "USB Overcurrent!".
Even though it was a Polyfuse or some other device, removing 5V
from the rail, that fed the #OC signal. There are a multitude of
#OC signals, so more than one channel can be monitored.

On USB2 ports, one fuse is shared by the two ports in the stack.
This is to reduce component cost. Included in such circuits, is a
100uF electrolytic cap, to prevent voltage sag, when a load is
first plugged in. (This prevents downward-going transients on
the VCC pin on the USB port.)

I have one motherboard here, where a single fuse is shared by
two USB ports, the mouse and keyboard connector, the parallel port
and something else. That's a reason why you have to "open the
equipment and look", to understand why the design seems so flaky.
The rest of my motherboards, seem more consistent.

    Paul