ATX power supply power switch

Hi,
I am planning on using an ATX power supply in a kiosk type
application, and I am trying to figure out what to do with the power
switch.
The ATX power supply has a normal on/off AC switch, which is what I
would
like to use. However, this only puts the supply in standby mode.
The power switch on the front of a PC, pulls the PS_ON line to ground,
which
turns on the rest of the supply.
What I am not sure, is if I can keep the PS_ON line permanently tied
to ground,
or is it just a momentary input? Can it do any damage to the supply if
I keep it hardwired to ground?
Thanks,
Allen

You can keep it tied to the ground permanently, no problem.


Piotr


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Piotr Stawicki wrote:
> You can keep it tied to the ground permanently, no problem.

Except that it won't necessarilly work.  I had a similar situation and was 
appaled to find there was no consistent way to assure an ATX power supply 
will turn on without the momentary ON signal.  It is a rather silly 
oversight IMHO. 

John Harlow <sirsausage@hotmail.com> wrote:
> Piotr Stawicki wrote:
> > You can keep it tied to the ground permanently, no problem.

> Except that it won't necessarilly work.  I had a similar situation and was 
> appaled to find there was no consistent way to assure an ATX power supply 
> will turn on without the momentary ON signal.  It is a rather silly 
> oversight IMHO. 

Not from the point of view of the intended usage, I'd say.  I don't
think ATX was ever intended to be used in unattended systems.  Nor was
it ever planned to *have* a primary-side power switch in an ATX system
--- it's supposed to be always-on on the primary side.

Anyway, the issue is quite moot since most BIOSes let you configure
the mainboard to do this for you.  "Automatic AC power loss restart"
is what this feature is often called.

-- 
Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

"Hans-Bernhard Broeker" <broeker@physik.rwth-aachen.de> wrote in message 
news:2rq40fF1da3k5U2@uni-berlin.de...
>
> Anyway, the issue is quite moot since most BIOSes let you configure
> the mainboard to do this for you.  "Automatic AC power loss restart"
> is what this feature is often called.
>

... Which will work if he is actually planning to use an ATX motherboard of 
some kind and his BIOS has that option.

If not, then a simple way to guarantee proper startup is power a small 
microcontroller from +5STBY, have it monitor the +5V line or 'Power good' 
and pulse the ON/OFF line if power isn't present after a short time.

Rob

> If not, then a simple way to guarantee proper startup is power a small
> microcontroller from +5STBY, have it monitor the +5V line or 'Power
> good' and pulse the ON/OFF line if power isn't present after a short
> time.

Or a simple 555 timer circuit or similar. 

> You can keep it tied to the ground permanently, no problem.

Sure, no problem - except that it will probably shut the entire unit
down after a couple of seconds of powerup. The switch-on signal has to
be momentary. I suggest a one-shot powered off the +5V standby power
line.

Now I'm shooting from the hip, but if only a momentary signal is
required, couldn't you just tie the PS_ON to ground through a
capacitor?  This would  pull the signal to ground until the cap
charges, and toggle the power supply on.

-Jim


Hans-Bernhard Broeker <broeker@physik.rwth-aachen.de> wrote in message news:<2rq40fF1da3k5U2@uni-berlin.de>...
> John Harlow <sirsausage@hotmail.com> wrote:
> > Piotr Stawicki wrote:
> > > You can keep it tied to the ground permanently, no problem.
>  
> > Except that it won't necessarilly work.  I had a similar situation and was 
> > appaled to find there was no consistent way to assure an ATX power supply 
> > will turn on without the momentary ON signal.  It is a rather silly 
> > oversight IMHO. 
> 
> Not from the point of view of the intended usage, I'd say.  I don't
> think ATX was ever intended to be used in unattended systems.  Nor was
> it ever planned to *have* a primary-side power switch in an ATX system
> --- it's supposed to be always-on on the primary side.
> 
> Anyway, the issue is quite moot since most BIOSes let you configure
> the mainboard to do this for you.  "Automatic AC power loss restart"
> is what this feature is often called.

"Rob Turk" <wipe_me_r.turk@chello.nl> writes:
> "Hans-Bernhard Broeker" <broeker@physik.rwth-aachen.de> wrote
> >
> > Anyway, the issue is quite moot since most BIOSes let you configure
> > the mainboard to do this for you.  "Automatic AC power loss restart"
> > is what this feature is often called.

Where does one find this for say Windows XP?

> .... Which will work if he is actually planning to use an ATX
> motherboard of some kind and his BIOS has that option.
> 
> If not, then a simple way to guarantee proper startup is power a small 
> microcontroller from +5STBY, have it monitor the +5V line or 'Power good' 
> and pulse the ON/OFF line if power isn't present after a short time.

Interesting:  Bootstrapping the bootstrapping the bootstrapping.

Where is the uC getting the power to operate to ensure
the power supply has started?

> > If not, then a simple way to guarantee proper startup is power a small 
> > microcontroller from +5STBY, have it monitor the +5V line or 'Power good' 
> > and pulse the ON/OFF line if power isn't present after a short time.
> 
> Where is the uC getting the power to operate to ensure
> the power supply has started?

+5STBY is the "standby voltage", provided at all times while the PSU
is plugged in, specifically for circuits like this (and WOL and other
similar frippery).