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[aprssig] power on DB9 connector standard for trackers?

Robert Bruninga bruninga at usna.edu
Wed Dec 1 14:02:22 UTC 2004


>>> tburnett at vermontel.net 11/30/04 9:13:37 PM >>>
>You could put a small resister in parallel with the 
>regulater to carry part of the 140 ma...

Or...
The mA rating is probably more related to the power the
device can handle not just the current.  Thus, if the input
voltage is 12 to 14 volts from a car, then 5 to 7 volts
at 140 mA have to be dropped and dissipated by the regulator.
or .14 * 7 or almost one watt which is a lot of heat!

My approach would be to put a resistor in series and 
let it take more of the heat and yet still let the regulator
regulate perfectly.

In this case R=E/I so you want a 5/.14 or a 33 ohm
one watt resistor in series.  It will get hot, but not the
regulator which will only have 2 volts or so across it
at 140 mA or only 1/3 of a watt which it can do easily.

Just a thought.  And if the resistor smokes it fails safe
instead of taking out your GPS and tracker...

Bob, WB4APR




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