[ale] OT: Charging smart phones

[cfowler at outpostsentinel.com (Chris Fowler)]

On 10/24/2012 05:44 PM, Matt Hessel wrote:
> Most of the newer phones pull higher current and the chargers grow to match.
>
> I have chargers to miniusb that can't handle enough for my phone.
>
> I found that you need to check the sticker on the charger for the
> amperage.  Most are around 500 mA or half an amp.  Newer chargers can go
> from 750mA to 2amps.
>
> The car charger for my dual core phone is 750mA.
>
> The kindle fire charger i have at home is 2.2 amps.  That charges up my
> phone in half the time.
>
> Fyi.  Normal usb 2 ports supply 500mA  the usb 3 spec takes it to 2 or 3
> amps.
>

The USB DCP spec uses voltage dividers on D-/+ lines to "tell" the 
device how much current it can draw.  I believe this is how the TB 
determines "AC Charging" vs "USB Charging".


http://www.ladyada.net/make/mintyboost/icharge.html

I originally thought the rating on the adapter was good enough, but I'm 
learning it is more complicated than that.