@hippy I believe it is there to protect the RasPi, not the PSU. There is just a lot of confusion right now. They were allowing the LAN9512 to for power management of the USB ports and I have seen nothing that states that has changed. The only real change is the voltage and protection of the input power. The 5v always went to the USB ports, through poly fuse. Did anyone hear that they have made any other changes? As far as I know the LAN9512 still handles power management to the USB ports. The question is how much power can we get at those ports.
From liz:
There is a polarity protection diode. There\'s a voltage clamp, and there\'s a self-resetting semiconductor fuse. We do think about these things!
From Gert van loo:
Using linear regulators means the device will use more then the originally promised one watt. (Sorry but the price promise is what we really had to keep). I have written a document to explain why for the non-electronic engineers subscribers.
http://www.scribd.com/doc/69700160/Rasp ... More-Power
From Gert van loo:
Yes the 5V coming in goes straight to the USB. (Apart from the fuse of course.) As things stand now that 5V net is also connected to two pins on the GPIO connector. I have had some questions about that: is it 5V in or 5V out, on which I answered that a 5V copper strip does not have \'ins\' or \'outs\'.
If you really want to you can replace the fuse with a bigger one and you can connect two 1A consuming USB devices. Just make sure you pump enough current into the board. There probably is an upper limit at which the copper tracks are not sufficient for the current but I don\'t know where that is and we are then talking silly currents....
From Jacklang:
Aarrgh!
I say again 0.7A is including power drawn from the USB ports when the board acts as a host. RPi board on its own is much less, and it.
Lobo: This was in reply to someone asking if it would draw 700ma continuos.
From Gert van loo:
0.7A should be sufficient to power the BCM2835 + LAN9512 + HDMI + two USB ports drawing about 100mA each. As with most electronic equipment: under power a bit and it will give you unreliable result . If you under power a lot it will fail spectacularly. I honestly don\'t know what happens if you under power it and write to the SD card at the same time....
From Gert van loo:
abishur: Thanks Gert, is 100 mA a max for the USB ports or can they take more if I use a higher amperage PSU?
see my post in this forum from 17:59. You have to use a bigger fuse.
radix: what will be the maximum safe current passing through raspb ??
See my last remark post in this forum 19:50. But that was not serious. You never supply big currents from a distance unless you\'re desperate. You just get noise and voltage drop. Just don\'t!
That is why big USB drives have their own power socket.
Ok so here are the posts that concern the new power scheme, all from the \"power supply news\". So now you can see where the 100ma per port came from but you can also see that it is possible to give more power to the USB ports. I do not see anything that says that there is no power management to the USB ports.
So what I see here is Gert is stating that the RasPi B model \"may\" draw as much as 500ma (2.5watts?) without the USB ports drawing. I do not think they will know for sure what the draw is going to be until they have one in their hand. So if you replace the fuse to 1amp then you could get 250ma per port. Can we go up to 1.5amps? The micro USB connector can supposedly take up to 1.8amps. This would allow the full 500ma max by USB 2.0 specifications, maybe. There is an awful lot of guesstimating all through this mess, including on my part.
EDIT: this does not mean that the RasPi will draw 500ma (2.5watts). I believe Gert van loo gave a high estimate of what the RasPi might use.
Note: DO NOT try to put 2.5 amps into the board. Gert van loo was being facetious there. The connector maxs at 1.8amps. It might take it, or it might create pretty blue smoke. I vote on the smoke if I get a vote. And yes you can get a 2.5amp 5v adapter. Not in micro USB though, I think it is mini USB for the beagle board.