ATX power suply

[fredybc]

It there any way to make an ATX power suply switch on automaticaly after a power fail? I mean, if I have a server with a no-break and an ATX power suply and my sno-break fails and my power company fails too, when I get power again my system won´t be on, so I want to know if I can do anything internally (electronic changing something) to make the ATX PS switch on.

[Banti]

This should be a bios setting that you can enable.

Check your motherboard manual.

Banti

[Bovon]

The only way to restart an ATX power supply is to short the two pins where the case switch connects. An ATX power supply has two seperate supplies. A 5 volt supply that runs continusly when it is plugged into the wall socket. This controls the main supply by way of the mainboard connection. There is a way to have it turn back on after a power failure and it goes off, but this would take a relay (or solid state) control device. What that would do is, after the power comes back on, a timed relay (or solid state) circuit would momentairly put a short on those two pins, and this would again re energize the main supply.

[Psycho Logical]

"An ATX power supply has two seperate (sic) supplies.
A 5 volt supply that runs continusly (sic) when it is plugged in..."
Both statements are incorrect. There is only one power supply.
+5v standby is a separate rail or lead from the (one and only) power supply.

"The only way to restart an ATX power supply is to short the two pins..."
"...this would take a relay (or solid state) control device."
Not necessarily. And a huge waste of time and money.

Let's not re-invent the wheel. Or use a sledge hammer to swat a fly.

In the BIOS Setup utility program for an Award BIOS, look for:

CHIPSET FEATURES and/or POWER MANAGEMENT SETUP

Power-Up State - (Response after a power failure)
-- Options --
• Stay Off - keeps power off until power on/off button is pressed
• Last State - restores previous state before power failure
• Power On - restores system power regardless of previous state

Soft Off by PWR BTN
-- Options --
• Delay 4 sec - button functions as reset/suspend button
• Instant Off - button functions as on/off switch

Hardware Reset Protect
-- Options --
• Enabled - power/reset button will not function
• Disabled - power/reset button will function as normal

Power On Function
-- Options --
• Button Only, Keyboard 98, Hot Key, Mouse Left, Mouse Right
(This function allows you to set the method by which your system can be turned on.
It should be set to Button Only so your system will only start with the power button.)

Not all options above may be available, depending on the BIOS version and date.
You may have to make changes to some or all of these options to get the right combination.

There may be different settings or terminology for an AMI BIOS.

[Bovon]

Originally posted by Psycho Logical
"An ATX power supply has two seperate (sic) supplies.
A 5 volt supply that runs continusly (sic) when it is plugged in..."


Both statements are incorrect. There is only one power supply.
+5v standby is a separate rail or lead from the (one and only) power supply.

I beg to differ sir, an ATX PSU actually does have a 5 volt supply that runs all of the time the supply is connected to an AC power source. This is what controls the on/off of the main supply.

If there were not a voltage present to turn it on, what does turn an ATX supply on?. There certainly is no switch such as the AT supplys have, so it must be electrical...right?..if its electrical, where does that come from, if not the psu.

When I indicated there were two 'separate' supplies, I ment that the main psu has two voltage supplies within one case, one...a 5 volt, runs 'continuously' and its function is to control the main supply.

Let's not re-invent the wheel. Or use a sledge hammer to swat a fly.

There may very well be alternate means to re-energize an ATX psu from Windows/bios setup, this I am not familiar with. Having spent 40 years in electronics in control circuits, this naturally came to mind.

Thank you for calling to my attention my shortcomings with spelling. I shall endeavor to be as correct as you are in the future.

[DanU]

"An ATX power supply has two seperate supplies. A 5 volt supply that runs continusly when it is plugged in..."

Both statements are incorrect. There is only one power supply. +5v standby is a separate rail or lead from the (one and only) power supply.


Whether it's two power supplies or one is a matter of semantics. From a circuit perspective, I can see where Bovon is coming from, since the +5V standby supply is very distinct from the rest of the circuit. Of course, when viewed as a whole, most folks would just refer to it as a single power supply. Whatever you decide to call it is up to you, but in my book, both views are correct depending on how you look at it. BTW, a while back Bovon posted a nice link to an ATX power supply schematic. You can find a copy of it on http://www.technick.net/cir_ps_atx200.htm if you're interested.

Bovon is most certainly correct about +5V standby being on whenever the ATX supply is plugged into a live outlet. There is just one exception... on some ATX PSUs there is a switch in the back. Turning this off will de-energize all of the outputs, +5V standby included.


Thank you for calling to my attention my shortcomings with spelling. I shall endeavor to be as correct as you are in the future.


Orthography was never my forte either :p

[fredybc]

Thank you all for answering my question and I will do some eletronical modifications to the psu.

[DanU]

Does your BIOS not support automatic power-on after a blackout/power failure?


Power-Up State - (Response after a power failure)
-- Options --
• Stay Off - keeps power off until power on/off button is pressed
• Last State - restores previous state before power failure
• Power On - restores system power regardless of previous state

[Bovon]

Hi DanU Yep, I forgot that some supplies have a power switch included. I have not seen a psu with a switch on the psu sence the older AT days, but I know the newer ATX (and possibly newer AT supplies) have a switch.

I also can see both points of view here as well...If a OS or bios does not provide a way to re energize an ATX psu after a power failure, it can still be done with an external momentary shorting circuit applied to the two pins on the motherboard in parallel with the case switch. I have designed and built many simular circuits, one was even for a computer several years ago when a friend wanted his AT system to stay off after a power failure and he was not present to comtrol the power up when the AC came back on. As you know, an AT type psu will re energize after a power failure and the AC comes back on because of the positive mechanical type on or off switch on the case.