On 12/11/2010 15:59, Adam Field wrote: > On Fri, Nov 12, 2010 at 8:20 AM, V G wrote: >> On Fri, Nov 12, 2010 at 7:53 AM, Olin Lathrop= wrote: >>> Not necessarily. USB voltage at the device can be from around 4.3 to 5= ..5 >>> volts worst case if I remember right. Probably the phone contains a >>> switcher to charge its battery and you don't need to be right on 5 volt= s in. >>> Give it a try with a variable power supply to test it. >> Yes, I'm going to experiment with voltage on my $700 phone. > If Olin is correct, which he usually is on these things, then every > time you plug your phone into a USB port to charge, you are > "experimenting" with it. > > As an aside, I bought a cheap cigarette lighter inverter rated for 90W > 120V, but it also had a USB port on it. Turns out the 5V on the USB > plug was regulated by a 7805 with a tiny heatsink. After 5 minutes of > charging my phone I smelled burning. Nothing was damaged, but the poor > regulator was probably dropping 7V at 500mA-1A, while it was probably > only rated for 2W. Stupid designs involving USB are everywhere, and > I'm sure the phone manufacturers know this and build in some > protections so they aren't getting phones returned under warranty. > Partly the "real" USB spec, not Apple's made up one. says a Max of=20 500mA. not 1000mA. There are many Apple devices that take more than a=20 standard USB port is supposed to supply. The earliest USB spec is 100mA but 14.2 - 5 =3D 9.2V Thus 4.6W when engine running and full 500mA. You=20 need a serious heatsink for 4.6W on even a 78M05 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .