Hardware Reference
In-Depth Information
If you have a charger for most Android phones, you have the Pi's power cable (sorry,
iPhone fans). It is possible (but not the best scenario and might not work at all) to plug
the other end into the USB port of your computer rather than the wall. And for other
projects, you'll want to get power through the GPIO. That said…
Think Twice Before Using the GPIO to Power the Pi
Before you rush to input 5 V over the GPIO pin, remember that when you do this you're
bypassing the hardware's input fuse. That fuse is there to protect your hardware in
case of malice or stupidity.
For example, imagine that you think you're passing 5 V, but you're actually passing
more than that into the Raspberry Pi via the GPIO. That might be because you weren't
entirely clear on what you were doing, or it could just be an accident. Either way, out
comes magic smoke! And by “magic,” we mean, “that project just disappeared like a
bunny in a hat!”
Plenty of power supplies aren't perfectly “clean,” meaning it might say “5 V,” but what
it means is “more or less 5 Vish.” Even if it just spikes above 5 V, you're bypassing
the transient-voltage-suppression (TVS) diode!
That diode is what would normally protect the Raspberry Pi from those unexpected
voltage spikes (by shunting away the excess current when it exceeds the avalanche
breakdown potential), but you're just going right around it. And then out comes the
magic smoke.
Last, but not least, you have to put regulated 5 V into the GPIO, and most power
adapters do not output regulated voltage. This means you need to have a voltage
regulator circuit between the GPIO pin and the power adapter.
For all of these reasons, we highly recommend you just feed power into the Micro USB
Type B port, unless you have a truly excellent reason not to.
Do Not Backpower the Pi over USB
Hack #08 explains how some USB hubs will backpower over the interconnect cable,
which can actually partially power the Raspberry Pi. Do not do this.
USB hubs are not supposed to backpower. This is not regulated or reliable power in
any real sense. It can (and likely will) result in unpredictable behavior including (but
not limited to) unexpected program failures, kernel panics, and SD card corruption.
 
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