ARMweb power supply

Question about power
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YahooArchive
Posts: 1463
Joined: Fri Oct 19, 2012 5:11 am

ARMweb power supply

Post by YahooArchive » Tue Dec 04, 2012 1:46 am

> I find that it gets very hot. Is this normal?
> The regulator device is the hottest component.
> I have a 7v external supply. .

Your 7V supply is probably putting out more than 7V, and with the
current of about 200-250 mA of the board is too much power for the
regulator to dissipate.

Its much better to use a regulated supply for the ARMweb. In the US
5V regulated supplies are becoming common as they are used in some
settop cable devices.



YahooArchive
Posts: 1463
Joined: Fri Oct 19, 2012 5:11 am

Re: ARMweb power supply

Post by YahooArchive » Tue Dec 04, 2012 1:46 am

Thanks, I think you are correct.

I measured the power adapter at 8.5v mean with 0.5v ripple.
I measured the current at 180mA, which is a total of 1.53w,
of which 0.85w is dissipated in the regulator. Reducing the
supply to 5v will certainly make it run cooler.

Using my very accurate temperature sensor , back of finger ;-)
I calculated that 180mA @ 3.3v power was mainly being dissipated between
the 2138 and the Ethernet I/F chip, with 2x power going to the Ethernet
chip. This puts the 2138 down at under 60mA. Which is not far
from the expected datasheet value. So I need not worry about
floating input buffers!

-mike

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