how to get 3.3v for pson signal? also inverted signal?(expert question)

**blackcar** · 03-26-2009, 03:32 PM

ok, another question, this one is harder
I have a small form factor motherboard (it's already got a 2.4G P4 with 1gb memory)
it's made by compaq which is a problem because they use non-standard power supplies

grrr...
I've spent days googling this and so far I've found that it will need a 3.3 PSON for a signal to power up the mother board.

interestingly someone online had made a device for this
when he rigged up a way to use the mobo with a standard ATX power supply (he's got some pretty ingenious electronic hacks on his website)
http://karosium.com/index.php?/archi...onversion.html
He uses 2 resistors (plus some other parts) to bring the 5v signal down to 3.3v.
I understand what the 2 resistors do, but why are the other parts needed? (see his diagram)
Can't i just get away with the 2 resistors to trim the voltage down to 3.31v? Or is the power still not close enough to 3.3?

so when trying to set this up, there are 2 problems that need to be resolved:

3.3v standby voltage
inverted PSON signal

also I don't fully understand what an "inverted PSON signal" is.

also I noticed this comment:
"There's the option of hardwiring the PSON (perhaps to a switch, which would essentially be like an old AT psu functionality-wise, with the added trouble of having to switch the mobo on/off separately) , but that's highly inconvenient"
Why wouldn't this be a good thing? aside from having 2 switches?

thanks

on a side not if anyone ever needs the specs for the compaq psu/mobo check this page
http://pinouts.ru/Power/compaq_pdp_power_pinout.shtml

**colin** · 03-26-2009, 04:06 PM

The extra parts involve a voltage regulator and an isolator.

The regulator is an LM-317 which is a simple adjustable regulator. You could probably just form a simple voltage divider circuit instead to save yourself some parts.

The "inverted PSON signal" just means "standard ATX psus power on if the PSON line is low, apparently the Compaq PSU is the exact opposite." Because of this, the motherboard would output a high signal all just to turn on, and a low at any other time. Any standard PSU would see the low as a signal to turn on, and therefore, it would always be on.

The hardwiring of the PSON signal would mean that your motherboard could never turn off your power supply (I think). Your power supply would never be in standby mode and waiting for the PSON signal to be sent from the motherboard, instead, it would always be on with the fans blowing and etc. For a car application, it doesn't seem like too big a deal...

**Enforcer** · 03-26-2009, 04:28 PM

A thread that might be of interest

http://www.mp3car.com/vbulletin/powe...er-supply.html

**blackcar** · 03-26-2009, 09:14 PM

Originally Posted by Enforcer

A thread that might be of interest

http://www.mp3car.com/vbulletin/powe...er-supply.html

yeap I saw that one, I had pm'd greenglo to see if he ever did resolve it, but I don't think he's on this board anymore....

the diagram "COMPAQ_M1-atx_sch.pdf"
has different pin numbers then the other diagram used by Karosium http://pinouts.ru/Power/compaq_pdp_power_pinout.shtml
wire colors a different too
so this kinda threw me off
reading over it again, seems like I only need a "TL192" and I think a 1k resistor?

Lemme see if I can get my hands on a TL192
and a decent DC/DC power supply and I'll play around with it

thanks for the reply

**blackcar** · 03-26-2009, 09:17 PM

Originally Posted by colin

The extra parts involve a voltage regulator and an isolator.

The regulator is an LM-317 which is a simple adjustable regulator. You could probably just form a simple voltage divider circuit instead to save yourself some parts.

The "inverted PSON signal" just means "standard ATX psus power on if the PSON line is low, apparently the Compaq PSU is the exact opposite." Because of this, the motherboard would output a high signal all just to turn on, and a low at any other time. Any standard PSU would see the low as a signal to turn on, and therefore, it would always be on.

The hardwiring of the PSON signal would mean that your motherboard could never turn off your power supply (I think). Your power supply would never be in standby mode and waiting for the PSON signal to be sent from the motherboard, instead, it would always be on with the fans blowing and etc. For a car application, it doesn't seem like too big a deal...

Hi Colin,
I'll look into "simple voltage divider circuit"
I would like to just use resistors to get to an exact 3.3v

also thanks for the "inverted" explanation

**Enforcer** · 03-26-2009, 09:27 PM

Originally Posted by blackcar

yeap I saw that one, I had pm'd greenglo to see if he ever did resolve it, but I don't think he's on this board anymore....

the diagram "COMPAQ_M1-atx_sch.pdf"
has different pin numbers then the other diagram used by Karosium http://pinouts.ru/Power/compaq_pdp_power_pinout.shtml
wire colors a different too
so this kinda threw me off
reading over it again, seems like I only need a "TL192" and I think a 1k resistor?

Lemme see if I can get my hands on a TL192
and a decent DC/DC power supply and I'll play around with it

thanks for the reply

Well I picked up some of those optocouplers but never got around to using them as I moved from my Compaq PC to a home made one.

**blackcar** · 04-07-2009, 04:43 PM

Enforcer, do you still have the spare ones you picked up?

**blackcar** · 04-10-2009, 12:53 AM

Originally Posted by colin

The extra parts involve a voltage regulator and an isolator.

The regulator is an LM-317 which is a simple adjustable regulator. You could probably just form a simple voltage divider circuit instead to save yourself some parts.

The "inverted PSON signal" just means "standard ATX psus power on if the PSON line is low, apparently the Compaq PSU is the exact opposite." Because of this, the motherboard would output a high signal all just to turn on, and a low at any other time. Any standard PSU would see the low as a signal to turn on, and therefore, it would always be on.

The hardwiring of the PSON signal would mean that your motherboard could never turn off your power supply (I think). Your power supply would never be in standby mode and waiting for the PSON signal to be sent from the motherboard, instead, it would always be on with the fans blowing and etc. For a car application, it doesn't seem like too big a deal...

I have a opus 150w coming in
looking at the opus specs
Output: 150W
+3.3V: 10A max, 13A pk
+5 V: 10 A max, 13A pk
+12 V: 5 A max, 6.5 A pk
-12 V: 0.5 A max, 1.2 A pk
5 V standby: 1 A max, 1.2 A pk

I think I can skip the 5v to 3.3v conversion by putting a switch on to connect the green and white wires (that lead from the opus "PWR SW" to the "ATX soft power switch")

can some confirm if I am right?

If I am right that switch should now turn the power supply on or off (eg power supply will send full voltage to the motherboard)
Then I can tap the 3.3V coming off the psu to feed standby voltage to the MB
Or do I even need to bother with the 3.3V anymore as I have a separate switch to activate the PSU??

I still need a optocoupler to invert the signal from the power supply to the motherboard.

**blackcar** · 05-08-2009, 08:02 AM

OK, I have a circuit built that provides 3.3 V and an inverted signal for the PWR_ON to the motherboard

(circuit was designed by owner of this site: http://karosium.com/ )

I was able to measure the 3.3 + volts with my volt meter.
but what should I see as the inverted signal?
my voltmeter shows .08+ volts is that right?

layout of wiring:

thanks