Re: USB 802.11 adaptor

[Pär Moberg <ghostdewolf%gmail.com@localhost>]

The Raspberry Pi has a fuse, f3, rated at 1 or 1.1 (A)mpere. The
Raspberry Pi model B under full load takes aproximatly 700mA or 0.7A
and 310mA or 0.31 A under no load running linux. This means that
everyting connected to the USB ports and GPIO header has to draw less
than 700mA to 300mA.

This is why you have to have a powerd USB hub or do some sort of
hardware hacking. The speed might be USB 2.0 but the power is most
defenetly not.

On 19 March 2013 23:00, Jared D. McNeill <jmcneill%invisible.ca@localhost> 
wrote:
> These fuses were removed in rev. 2 RPI IIRC.
>
> On 2013-03-19, at 5:54 PM, Jochen Kunz <jkunz%unixag-kl.fh-kl.de@localhost> 
> wrote:
>
>> 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.
>> --
>>
>>
>> \end{Jochen}
>>
>> \ref{http://www.unixag-kl.fh-kl.de/~jkunz/}
>>
>