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Subject: Re: Car Battery Supply
Organization: Nobody nowhere
X-Newsreader: Microsoft Outlook Express 6.00.2720.3000
Date: Tue, 14 Jan 2003 21:37:16 -0000
NNTP-Posting-Date: Tue, 14 Jan 2003 21:37:21 GMT
"Sean Burns" wrote in message
> Hi All,
> Has anyone got a good example schematic of how to power a digital circuit
> from +12V car power supply?
> I am of the understanding that the supply is quite crap - what voltage can
> it drop to and what kind of artefacts can be seen on the supply? How do I
> protect against these artefacts?
Yeh the car line voltage does vary a bit. 12V when the engine is not running
and 13.8 when running. And the voltage can drop quite a bit when the engine
is being cranked. If your just powering a small 5V logic circuit then a 7805
regulator will to fine. Put a 16V zener across the input, to stop any high
voltage spikes. And a large 10,000uF cap across the input aswell to maintain
the voltage to the regulator during engine cranking.
A thyristor crowbar with fuse protection across the output would not hurt
either, just in case the reg goes short.
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