Hi! I've read on this website that the mbed NXP LPC1768 might be powered by USB or +4.5 to +9v applied to VIN, but the diagram shown in the card that I got with the uC says that it might be powered by +4.5 to +14v. Is that card wrong? I also have another question: would there be any problem if I use an externalvoltage supply for the uC and then I connect the USB? would the uC ignore the USB voltage supply? Thanks!

Check this thread.

and this one

Thank you! That answered my first question, but i've not read anything there about plugging the USB whilst Vin is connected to an external voltage supply. Which voltage supply would be ignored?

I have several mbeds running with both Vin and USB power at the same time. Neither supply gets "ignored," but if Vin is higher than 5V it will supply most of the current to the device. I have a 7805 5V regulator in the circuit before Vin (mainly for other devices the mbed talks to), so I don't know how well it works with Vin above that.

The mbed circuit has two LD1117S33 3.3V regulators, so as long as you don't exceed the input voltage and current limits, you should be fine. The inputs are diode protected, so you won't backfeed the USB power or anything like that.

Just remember that with power to both inputs you'll have to explicitly reset the CPU when you need to, since removing just one of the power sources does not cause a reset.

Regards,

- Gary

You'll be okay as long as you don't exceed the input voltage, load current and POWER DISSIPATION. IIRC the specs say 100 mA supply current without Ethernet and 200 mA with. At 5V input and 200mA the power dissipation is .34 W. At 10V in and 100mA the power dissipation is .67 W. There isn't much heat sinking on those regulators. But they are temperature protected so if you do overload them you won't damage them. But I wouldn't want to run them at a high temperature for very long, that does ultimately lower their life.

why when I hit two mbed to power off both? It is likely to have left me mbed defective