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Thread: [EE]: +12V and +5V in automoble
www.piclist.com/techref/power/batterys.htm?key=12v
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face BY : Dan Michaels email (remove spam text)



Thomas C. Sefranek wrote:
>Richard Sloan wrote:

>> Yes heat is an issue that needs to be addresses also as a 7805 was attempted
>> and man does it get HOT!
>
>Ohms law:  12V - 5V = 7 volts at 1 amp, = 7 WATTS of heat.
>You can waste some of that heat in a 5 ohm resistor (5-10 watts) in series with
>the +12
>to the 7805.
>

Not the most elegant or cheapest solution, but you might also
consider small-V 5W zeners instead of a series R. I have one
item where I do this, but is Vz = 4.3v @ .3A, so only about
1.5W.

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Subject (change) [EE]: +12V and +5V in automoble

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