Hi,
Yes, it was a bit of a vague thing to say.. sorry about that.
The main power rail on the board is 3.3v, and so any voltage applied to Vin is regulated down to this using an LDO, which dissipates power as heat. For a given load current (mbed usually draws about 150mA) you can calculate how much power has to be dissipated as heat as Vin-3.3v * 150mA.
For Vin at 9.0v and nominal load current of 150mA, this equates to 855mW, which doesn't lead to significant increase in heat.
However, at 14.0v this power dissipation is 1.6w which is more significant in terms of temperature rise. When you then add in the fact that you can be drawing up to 400mA through the IO pins, the power dissipation of the LDO can lead to thermal shutdown - the LDO switches off so it can cool off.
While datasheets and a bit of maths can show you the power dissipation and heat rise for a given load current and a supply voltage, we are suggesting that unless you are willing to experiment, and work the numbers, you should keep Vin at 9v or below.
I have successfully run my mbed at 12v knowing that I will not be drawing any power through the IO pins, and understanding that the LDO will get hotter than usual.
If you are not sure, keep it below 9v.
Thanks,
Chris
> you show a picture of mbed Microcontroller.
> The "VIN" range is 4.5 - 14.0 In
> the VIN range is 4.5 - 9.0v IN
Thanks,
Chris