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Sheeva Plug goes AC/DC

The Sheeva Plug has served well as our RMS Gateway KE7KMN-10, but we needed a battery backup strategy. Radio and TNC are on 12VDC whereas the Sheeva Plug has an AC Power Supply which has a 5VDC@0.4Amps output.

The easiest way to convert 12VDC to 5VDC is using a 7805 linear regulator, but at 12 volts it would dissipate:

(12-5)X0.4=2.8Watts which is a fair amount of heat.

The efficiency is (5X0.4)/(12X.4)=41.6%. The regulator uses more power than the Sheevaplug!

A simple buck regulator can be cobbled together from a few parts, but there is a part available that puts a National Simple Switcher into the same footprint as a 7805 in a TO-220 package.

Looking at the performance data, we should see an efficiency of about 90%. I purchased a few of these from Digi-Key for less than $4 each, part number 811-2196-5.


One Response to “Sheeva Plug goes AC/DC”

  1. Bryan says:

    Basil reminded me that I showed this earlier this year at a club meeting and never published it.

    The battery current required now improves from 400ma to:

    400maX5V/90%/12V=185ma

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