-12dc from atx power supply

Aladdin · 01-01-2000, 12:42 PM

HEY GUYS, HAPPY MILLENIUM!!

Ok i dont think i have been using my -8v regulator properly while trying to get my sharp 6in screen to work. I have been connecting it to the +12vdc off of my atx power supply. After close inspection of jjohnsons website it appears that i should be connecting it to the -12vdc output. the only problem is i dont know which wire is -12v. Please let me know which wire the -12v is.

Further, being the electronics layman that i am, how ecxactly do i use the -8v regulator. there are three pins on it: do i hook the -12 v to one end, a ground in the middle and the third pin should output -8v or what? thanks for all the prvious help i have recieved on this site and thanks in adavnce for all the help i will surely need in the coming millenium

aladdin

jjohnson · 01-02-2000, 03:06 PM

Aladdin -

You are correct, the -12V line is the one you need to use. You have to change your thinking for negative regulators -- just remember you need a negative source to produce a negative output. That is why you cannot get -8V from +12V without special circuitry; -12V is the easiest available voltage on the PSU to derive -8V from.

The 7908 pinout is as follows (looking at the front, with the writing on it and pins facing down):

Pin 1: Ground (black wire on the PSU)
Pin 2: -12V input (blue wire on the PSU)
Pin 3: -8V output

The -12V wire on an ATX power supply should be blue in color. If you are looking directly into the ATX connector on the PSU, with the latching tab on the left, the -12V pin is the second pin from the bottom on the left column of contacts.

I hope this clears up some things. If it doesn't I can draw some diagrams to help you.

--Jason
http://www.m2pc.com