On Fri, 30 Aug 2002 10:14:18 -0400, you wrote:

>I need to build a power-supply to run a PC in a car, so I'm
>trying to figure out why I really need +/- 12V, which may be
>tough to produce with the ignition off (not enough overhead
>for the regulator).  I could build a DC-to-DC coverter that
>would raise the voltage, but that means $$$.
>
>Thinking of a regular desktop PC with a MB, audio card, video
>card, fan, and IDE drive only (no floppy or CD)...
>
>- MOTHERBOARD:
>    - 5V around board, which may be regulated to lower for
>      processor, etc, but that should not affect me.
>    - The motherboard has a 12V requirement (standard ATX
>      PS), but does it really need it, or does it pass on
>      the 12V to other devices?
>    - AFAIK, the parallel port does not require 12V.
>    - AFAIK, USB does not require 12V.
>    - Does the built-in serial require a +/-12V supply?  Or
Usually.
>      does it generate +/-12V (like a MAX232 for example)?
>      If I need to supply it, and decide not to use serial
>      comms, then can I just ignore it?=20
Probably - the only possible issue I can think of may be to do with
continually asserted ring interrupts.
> Or can I just supply
>      it with +/-5V (as an RS423 device) and make sure the
>      other end handles that level?
Possibly. May be easier to remove the RS232 driver and replace it with
MAX232 etc. +/-8v would probably work fine. =20

>- COOLING FAN:
>    - I can always get or modify the fan for 5V use, or I
>      could generate 10-ish volts for that.  So no prob
>      here.
>
>- AUDIO CARD:
>    - I believe line-out sound levels go to 10V, so +/-12V
>      is probably needed there.  Any way around this?
You may get away with less than 12V, as this is likely to give
headroom for the analogue stuff.=20

>Anything else I'm missing?
There may be things that use the 12V rail to get a clean 5v supply,
but 8v or so ought to do here. Probably most likely on audio or video
cards

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