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Re: USB 802.11 adaptor

On Tue, 19 Mar 2013 12:30:49 -0700
Andy Ruhl <acruhl%gmail.com@localhost> wrote:

> > The problem isn't total power consumtion, but short peaks that exceed
> > the max. 0.5 A for USB. This happens e.g. on sending a packet.
> Power supplies can often handle short spikes without a lot of impact.
> Depending on their design of course.
Often you can find electronic fuses on USB ports. They sense current
and switch power off of the asscociated USB port when the max. current
is exceeded. They are quite fast in doing this, so spikes from a WLAN
device may trigger them. (I am not talking about "poly fuses".) These
things are smal chips, e.g. in a SO8 package, and switch power by the
means of a MOSFET. Usually this MOSFET is controlable by the host CPU
to switch power on and some can trigger an interrupt if the current
limit is reached. E.g. the Olinuxino Mini uses a SY6280 for this.



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