Re: USB Power

On Aug 5, 7:29�am, John Devereux <jdREM...@xxxxxxxxxxxxxxxxxx> wrote:
Hi,

It seems the specification allows USB devices to draw up to 100mA (for
a "low power" port) and 500mA (high power port).

Does anyone have any idea of the incidence of high power ports?
Especially on laptops.

For a design with USB control, I am trying to decide if it is worth
including an option to take all the power from USB, rather than a
wall-wart type adapter. It would be great just to have the one plug,
and also allow fully mobile operation. But if a large fraction of
laptops only have low power ports, it may be more trouble than it is
worth. (It occurs to me that in order to support plugging in an
external hub, all laptop ports *ought* to be high power).

Thanks,

--

John Devereux

This is from memory -- becuase everytime I think "USB", I have to go
get the books - which are at the office.

So, I'll just mention this:
There are hubs, ports and controllers. I think controllers are all
high-power?? This is what would be on the laptop. Hubs would be
downstream from this, and could be either - or can also be powered
hubs meaning they have a wall wart. Ports are downstream from there
and are enumerated as either high or low power, standard, or high
speed, etc... Depending on what's available to be delivered to them.

I might have the actual terminology wrong, but the jist is right.

But as to low-power controllers on laptops?? I don't know. I
wouldn't think so.????
Someone here will know for sure. Good luck with the project.

-mpm
.

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