Interpreting PC Power Schemes
Interpreting PC Power Schemes
(OP)
Hi all, i'm attempting to design+build a regulated power supply for an old computer, and i'm trying firstly to make sense of the old stock supply, and how the load components fit into the scheme. Taking the hard drive for example, the faceplate says:
5VDC --- 0.66A
12VDC --- 0.24A
and the power cable setup is as such:
R B B B
e l l l
d k k u
+5V COM COM +12V
So am i to assume that there are two diff. major circuits, working out something like this?:
? ?
/ \ / \
| | | |
5 G G 12
and so the impedances would be 7.6 and 50. ohms, respectively. I'm guessing that the 12V is for the motor and servos and whatnot, and the 5V is for the logic? But I thought that most ICs could tolerate no more than ~20mA at their pinouts.
Thanks for any help. Would esp. appreciate direction towards resources dealing with power supplies and/or power schemes for components.
5VDC --- 0.66A
12VDC --- 0.24A
and the power cable setup is as such:
R B B B
e l l l
d k k u
+5V COM COM +12V
So am i to assume that there are two diff. major circuits, working out something like this?:
? ?
/ \ / \
| | | |
5 G G 12
and so the impedances would be 7.6 and 50. ohms, respectively. I'm guessing that the 12V is for the motor and servos and whatnot, and the 5V is for the logic? But I thought that most ICs could tolerate no more than ~20mA at their pinouts.
Thanks for any help. Would esp. appreciate direction towards resources dealing with power supplies and/or power schemes for components.





RE: Interpreting PC Power Schemes
You are sorta correct on the two circuits. They aren't really *separate* as they do indeed share the grounds.
Usually they are RED/BLACK/BLACK/YELLOW though if memory serves me correctly. BLUE is usually -5V
The currents required have nothing to do with the logic gate ratings.....
Yes! The 12 volts is for the platter motor. The 5V is for the logic and drive-to-mutherboard communications.
The really big question though is why on Earth would you EVER consider building a PC power supply?!?!? They are probably the lowest cost for what you get item sold. They are fairly complex too. They have timed output signals to tell the motherboard "power ready" etc. etc.
RE: Interpreting PC Power Schemes
but replying firstly to your question, I'm thinking of building it for the same reason that I'm making a gravity-driven rotary grinder out of wooden dowels and custom cut-and-filed gears and pullies: <i>there is simply no better way to learn.</i> Using rough figures, I'm thinking this system could top out at maybe around 1600 rpm. Now I could buy a good electric 3450 rpm rotary grinder for about $25, but what's to be learned that way? Sure, I payed attention in Physics class and I <i>know</i> about torque and angular motion well enough, but it was only once I started building and designing this sucker that I really started to understand either on a gut level.
Uh but that being said I wasn't aware of the timing scheme, I guess I'd always though that was coordinated once power was received at the motherboard. Well, I won't abandon it so easily. Do you happen to know of resources that detail this? Maybe there's a commonly available output-timing IC that would fit the bill.
But at any rate (I've really responded in a backwards fashion, haven't I?), thanks for the info. One of my power cables is red/blk/blk/yel, but all the others are as above.
Could you please elaborate on "The currents required have nothing to do with the logic gate ratings....."? I'm confused on that point— isn't there a lot of logic circuitry involved in a hard drive? Clearly I'm just misinterpreting what the values mean, or something like that, but elaboration would be helpful.
Oh an a minor note, no matter how haphazard my efforts may seem, I do actually try to be rather methodical. Right now I'm just trying to evaluate the system as a whole, figure out all of the major principles, and then I'll probably build some test modules like individual filters, PWM units, figure out power factor correction. If, by the way, you know of any resources for such things, that would be awesome. Thanks!
RE: Interpreting PC Power Schemes
RE: Interpreting PC Power Schemes
RE: Interpreting PC Power Schemes
The cables that are R-B-B-Y are for hard and floppy drives.
The two cables with a mix and blue wires are for the motherboard.
The drives have IC's with millions of logic gates in them.
This is what's consuming the 0.6A
RE: Interpreting PC Power Schemes
RE: Interpreting PC Power Schemes
The sequence for powering up of the different rails is also specific on many multi-rail chips.
Good Luck
johnwm
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RE: Interpreting PC Power Schemes
RE: Interpreting PC Power Schemes
"maybe they chose a different scheme to distinguish themselves, a proprietary scheme similar to Dell's?"
what I meant to say was similar as in both companies wishing to have proprietary schemes, not similar as in have a scheme actually like Dell's. Sorry. Is there any way to edit a post after it's been submitted? I've been on several boards where that's the case, it's really quite nifty.
RE: Interpreting PC Power Schemes
Since it is an AT power supply, I do not think there is any "smart" circuitry inside that allows WOL or such, so some power regulators with enough current should work in this case.
Remember too, that the switch is directly connected to the mains, unlike newer ATX power supplies that use a low-voltage rail for monitoring the power switch's status.
http://www.mrkenneth.com
RE: Interpreting PC Power Schemes
Look at some of the chips. They often have manufacturing time stamped on them below (or above) the type numbering.
Ex.
"9534" would mean week 34, 1995. (I.E. late August or so 1995
Of course, the board assembly is newer than the newest chip, but usually not more than a few weeks or months.