Monday, Jun 30, 2008 at 11:19
Hi Phil
>Does the laptop's battery absorb spikes?
Not really, although it may… a bit… sometimes… but probably won’t :) Once we start to talk about high frequencies (and transients, invariably, contain high frequency components) two devices connected by a piece of wire or circuit board track no longer have zero ohms between them – at high frequencies a piece of wire is not a short circuit – so even if the battery did absorb some of the energy other components a few inches away on the same pcb track may still see the full force of the transient.
>Come to think of it, doesn't the vehicle's
>battery absorb spikes?
See above.
>And why doesn't everything we plug into 12V,
>and everything in the car suffer this fate?
It would – except when we design electronics for vehicle use we go to _a lot_ of trouble to ensure they are properly protected against such conditions. I recently glanced over the circuits for a major module in the Holden VE Commodore and about 50% of the components were dedicated to electrical protection.
Rather than me re-write existing knowledge take a look at this application note by Harris Semiconductors – it gets a bit technical but gives a good explanation of the issue:
Suppression of Transients in an Automotive Environment
Mike Harding
FollowupID:
579039