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Subject: Re: worried about automotive spikes in homemade relay driver
Date: Sun, 06 Oct 2002 01:06:03 GMT
NNTP-Posting-Date: Sun, 06 Oct 2002 01:06:03 GMT
Organization: AT&T Worldnet
> refering to the diagram in the above page - the +5v is from the output side
> of a 12-5v dc->dc converter. Will this work if the ground for the emitter of
> the 2N2222 is the chassis or the battery ground?
Not sure I understand the question.... but here's some info.
Automotive transients are of two main forms.
Low impedance (load dump) caused when the battery line is
opened during full alternator output conditions. The resulting
positive transient is often clamped at ~40V at the alternator
...but still eminates from a ~2-5 ohm source and lasts milliseconds.
Can be quite nasty.
Put a TVS on the input of your box. Try:
High impedance caused upon turn off of typical vehicle loads.
The resulting positive and negative transients are not necessarily
clamped but eminate from a high ~50-100 ohm source and last
microseconds. Pretty tame.
Put a zener (with proper polarity) at the input of your box.
Lastly, here's a simpler solution for the driver:
Just for grins.... what's it drivin'?
(BTW) Bitmaps are blaphemous on the internet. Try JPEGS.
My modem is sweating profusely. ;-)
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