On Wed, 5 Aug 2009 01:37:49 +0100, "Arfa Daily"
put finger to keyboard and composed:


"Dave Plowman (News)" wrote in message
...
In article ,
Clint Sharp wrote:
Can anyone give a link to a site which covers modifying an ATX PS 12
volt rail to 13.8v in reasonably simple terms? I Googled for a couple
of hours last night and found answers from the bizarre to ridiculous.
The +12v output is rated at 20 amps and I only need 8 max.

Ahh, grasshopper, to modify the 12v rail first you must find the
voltage reference for the 5 v or 3.3 v rail, your journey will take you
into the realms of voltage dividers and the TL431.

Ain't got one of those.


Yes it has, Dave. With that particular supervisory IC, it's behind the
reference and feedback pins, and not an external discrete device, as I
previously explained ... If you're not understanding the principles of how
these things regulate, then I don't think you are going to get too far with
this project.

Arfa

AISI, the main rails are regulated via the error amp at pins 16, 17,
and 18. The OP would need to remove/modify the resistors at the IN
pin.

The TL431's at the FB2 and FB1 pins regulate the +3.3V and +5VSB
supplies. I don't believe they need to be touched. I suspect, though,
that the +3.3V regulator will be working flat out to bring the output
down, if indeed it can.

- Franc Zabkar
--
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