Newbie - ATX power supply
Padu
one of those, I'm supposed to test the behavior of some electronic gates
(TTL 7400 series).
In order to do that, I need a power supply (they recommend something between
7-12 V, minimum 100 miliamps). They use one 5-volt voltage regulator and two
electrolytic capacitors to supply clean regulated 5V to the breadboard.
The thing is that I already have a PC power supply spare, and I think I
could use it, and if I'm not wrong, the voltage coming out of a PC power
supply is already regulated (at least there are lots of electonic components
inside my power source).
My problem: the damn thing is an ATX power supply. There's no ON/OFF button.
The PC motherboard is responsible to send this signal to the power supply.
How do I simulate this signal to make the power supply working constantly?
Thanks
PS: I don't know if this is the most appropriate newsgroup to post this
question, if not, please advice.
Floyd Davidson
An ATX power supply is *perfect* for your needs. There are just
a few odd things you need to know about how it works... Below
is an article that I posted to a different newsgroup yesterday,
responding to a question of "how do I test an ATX psu". You'll
find all the information you need!
There are two requirements for an ATX power supply to "act
normally". One is the PS-ON lead (green wire) must be grounded
(to a Black wire). The other is there must be a minimum load on
the 5 volt line. I've looked around, and cannot handily find
any specification on what the "minimum load" must be though. It
seems that it is extremely small, and an old disk drive or cdrom
will be enough. Another guess would be a 25 ohm 5 or 10 watt
resistor, which would draw about 200ma of current across 5 vdc.
If you really want to test it, here's a proceedure, which assumes
a 20-pin plug (the colors would be the same, but see below for a
24-pin plug pinout).
1) Plug AC in.
2) Measure pin 9 (Purple wire). Should show about 5.0 vdc.
3) Measure pin 14 (Green wire). Should show some voltage
between 3.5 and 5 vdc. The exact voltage is not critical.
4) Unplug AC.
5) Put a load across the 5 vdc line. You can do this
by using an old disk drive, cdrom, or a resistor.
6) Jumper pin 14 (Green wire) to ground (any Black wire).
7) Plug AC in.
8) A. The fan should run.
B. All voltages should measure close to their
nominal values (Note that -5v and -12v may be
very poorly regulated).
Note that pin 14 is the PS-ON signal line, which is normally
wired to the on/off switching circuit on the motherboard. It
has a 1000 ohm pull-up resistor connected (internal to the PSU)
to the +5v Standby line, and if there is no other connection it
should probably read close to 5 volts. That voltage will cause
the power supply to be "off". The nominal switching point for
PS-ON is 0.8vdc, and standard operating voltages are less than
0.4 volts for "on" and more than 3.5 volts for "off".
Here is a list of leads on a 20 pin connector,
PIN COLOR NAME DESCRIPTION
------------------------------------
1 Orange +3.3V Power, +3.3V
2 Orange +3.3V Power, +3.3V
3 Black GND Ground
4 Red +5V Power, +5V
5 Black GND Ground
6 Red +5V Power, +5V
7 Black GND Ground
8 Gray PWR-OK Power OK
9 Purple +5V VSB +5V VSB
10 Yellow +12V Power, +12V
11 Orange +3.3V Power, +3.3V
12 Blue -12V Power, -12V
13 Black GND Ground
14 Green PS-ON PS Remote on/off
15 Black GND Ground
16 Black GND Ground
17 Black GND Ground
18 White -5V Power, -5V
19 Red +5V Power, +5V
20 Red +5V Power, +5V
And this is a list of leads on a 24 pin connector,
PIN COLOR NAME DESCRIPTION
------------------------------------
1 Orange +3.3V Power, +3.3V
2 Orange +3.3V Power, +3.3V
3 Black GND Ground
4 Red +5V Power, +5V
5 Black GND Ground
6 Red +5V Power, +5V
7 Black GND Ground
8 Gray PWR-OK Power OK
9 Purple +5V VSB +5V VSB
10 Yellow +12V Power, +12V
11 Yellow +12V Power, +12V
12 Orange +3.3V Power, +3.3V
13 Orange +3.3V Power, +3.3V
14 Blue -12V Power, -12V
15 Black GND Ground
16 Green PS-ON PS Remote on/off
17 Black GND Ground
18 Black GND Ground
19 Black GND Ground
20 White -5V Power, -5V
21 Red +5V Power, +5V
22 Red +5V Power, +5V
23 Red +5V Power, +5V
24 Black GND Ground
The -5 VDC line may not exist.
The +5 VSB supply is Standby Power, which supplys parts of the
motherboard which are always powered up (to allow options like
"wake-on ..." to work).
The PWR-OK line is at ~5 VDC if the AC input and the +5V and
+12V lines are within specifications. If either the +5V or the
+12V line falls to below the specified voltage tolerance or if
AC is lost for more than one power cycle interval, then PWR-OK,
will drop to ~0 VDC. (If it helps any, if AC is lost, PWR-OK is
supposed to drop at least 1 ms before the +5V and +12V lines go
below specified voltage tolerances!)
--
Floyd L. Davidson <http://www.ptialaska.net/~floyd>
Ukpeagvik (Barrow, Alaska) fl...@barrow.com
Padu
Thanks a lot
"Floyd Davidson" <fl...@ptialaska.net> wrote in message
news:87of58i...@barrow.com...
VortexOne
operate without any load. So if you plan to use this kind of power
supply make sure you have always a load attached (for example, a low
voltage light bulb, a power resistor etc.)
--
VortexOne
************************************************************************
vor...@hotmail.com
(Messages trashed without the word KEYWAY in subject line)
************************************************************************
w_tom
reason why all PSUs require specifications.
I believe Radio Shack sells something like a 10 ohm 10 watt
resistor. That would be more than sufficient load for an ATX
PSU.
This load requirement varies from supply to supply. Some
that required a minimum load often would still power up -
almost every time. Therefore they required maybe a 100
milliamps load. But again, that is why specifications are
always provided by a responsible supply manufacturer.
Welcome to TTL. Where supply meets test circuit, put at
least one 10 uf capacitor, +5 to ground. Also a 0.01 uf
ceramic capacitor is installed in the area of TTL power and
ground pins - maybe one capacitor for every three or five TTL
chips.
Superior than TTL is CMOS Logic. One basic difference.
CMOS inputs must always have a pullup or pulldown connection -
something that does not adversely affect TTL.
Anthony Fremont
"w_tom" <w_t...@hotmail.com> wrote in message
news:3E540B36...@hotmail.com...
> Minimum PSU load is a function of PSU design. Just another
> reason why all PSUs require specifications.
>
> I believe Radio Shack sells something like a 10 ohm 10 watt
> resistor. That would be more than sufficient load for an ATX
> PSU.
Not at 12V. 12V/10Ohm = 1.2A 1.2A * 12V = 14.4W Put two in series.
;-)
michael
w_tom
one has manufacturer's specs, then one cannot say how much or
if any load is required. It varies for every design.
Floyd Davidson
If that were what one wanted to do, three in series would be
suitable.
However, it isn't the 12v bus that needs a load. Either the 5v
or the 3.3v bus must have a load on it. 10 Ohms isn't a good
idea there either. Something like 25 ohms on the 5 volt bus
would be just fine. That will dissipate 1 watt, so a 10 Watt
resistor would be just fine... and two of these 10 Ohm 10 Watt
units in series would be OK too.
Anthony Fremont
> Anthony Fremont wrote:
> >
> > "w_tom" <w_t...@hotmail.com> wrote in message
> > news:3E540B36...@hotmail.com...
> > > Minimum PSU load is a function of PSU design. Just another
> > > reason why all PSUs require specifications.
> > >
> > > I believe Radio Shack sells something like a 10 ohm 10 watt
> > > resistor. That would be more than sufficient load for an ATX
> > > PSU.
> >
> > Not at 12V. 12V/10Ohm = 1.2A 1.2A * 12V = 14.4W Put two in
series.
> > ;-)
> >
> > michael
"w_tom" <w_t...@hotmail.com> wrote in message
news:3E5447CF...@hotmail.com...
> In many supplies, only a watt is more than sufficient. Until
> one has manufacturer's specs, then one cannot say how much or
> if any load is required. It varies for every design.
No qualms with that, I was only pointing out the potential for
overheating the resistor if he attached it to the 12V supply. I have no
idea what a "suitable" load would be for operating the supply like this.
As you said, I'm sure that it would vary by supply. ;-)
michael
Padu
of the available wires. Works perfectly.
This weekend I've tested the behavior of a NAND port (TTL 7400). Being a
software engineer, I know what's a NAND port and what it should behave like,
but for my surprise, I cought myself amazed when leds turned on and off with
my experiments.
I think I'm too used with 0's and 1's instead of 0V and 5V.
"w_tom" <w_t...@hotmail.com> wrote in message
news:3E540B36...@hotmail.com...
w_tom
solution is to find a book entitled "TTL Cookbook" or "CMOS
Cookbook". Concepts associate with digital logic are
explained. You now have a good platform to demonstrate what
you read.
Also learn about a famous chips called the 555. It is a
'classic' cousin to digital logic.