Power supplies have on/off switches now?

[Guest]

I'm noticing that all power supplies nowadays seem to have an on/off
switch on the back. My 5-year old Antec doesn't have one. What is the
point of this? Especially considering that they've now made it so that
you can't turn off a computer by just pressing the power button on the
case, you have to shut down the OS (at least with Windows you do). Now
all power supplies have an on/off switch, so you can turn off the
computer without shutting down the OS?

 

[Pelysma]

I'm noticing that all power supplies nowadays seem to have an on/off
switch on the back. My 5-year old Antec doesn't have one. What is the
point of this? Especially considering that they've now made it so that
you can't turn off a computer by just pressing the power button on the
case, you have to shut down the OS (at least with Windows you do). Now
all power supplies have an on/off switch, so you can turn off the
computer without shutting down the OS?

Not all, but many. I can see how this could cause problems if you used it
to turn off a running computer, but I believe the idea is to be able to turn
off the power when the computer is shut down, yet leave it plugged in and
therefore grounded. One would shut down the computer from the OS, then turn
it off at the PSU switch, then hit the power button once to bleed any
charges off the motherboard before opening things up.

Once upon a time the power switch on the front panel did just this, turn off
the AC to the PSU. Maybe after a few years of soft power switches, people
are beginning to see the virtue of having a hard AC switch available.

 

[Guest]

Now all power supplies have an on/off switch, so you can turn off the
computer without shutting down the OS?

Turning off that switch is just like pulling the power cord, which
usually causes problems with Windows.

 

[Guest]

Now all power supplies have an on/off switch, so you can turn off the
computer without shutting down the OS?

Turning off that switch is just like pulling the power cord, which is
usually bad for Windows.

 

[Conor]

I'm noticing that all power supplies nowadays seem to have an on/off
switch on the back. My 5-year old Antec doesn't have one. What is the
point of this? Especially considering that they've now made it so that
you can't turn off a computer by just pressing the power button on the
case, you have to shut down the OS (at least with Windows you do). Now
all power supplies have an on/off switch, so you can turn off the
computer without shutting down the OS?

Tell me, what do you do to turn off your computer if it locks up solid
due to overheating for example?

Me? I reach round the back and hit the switch on the PSU.

 

[Jim]

Many people use an UPS on/off switch to disconnect power from their PCs.
Another alternative is the under monitor power switching unit for many AC
powered devices.

Going back to when ATX was first introduced, my first ATX power supply had
the on/off switch in the back of it. So, its not a new concept.

If working properly, the ATX on/off switch will turn off most of the power
supply output. You have to hold the switch in for more than a couple of
seconds. There is still some power applied though as evidenced by some
onboard motherboard leds.

The power supplies that had a on/off switch connected directly to them were
AT power supplies. These are true on/off switches. The ATX versions are
momentary switches.
.............
Jonny

 

[Pelysma]

The power supplies that had a on/off switch connected directly to them
were AT power supplies. These are true on/off switches. The ATX versions
are momentary switches.
............
Jonny

The OP is noting exactly this: that many newer power supplies DO have an AC
switch exactly like the old AT back panel switch, independent of the soft
power to the motherboard.

I think, though, that it is intended to be used when the computer has
already been shut down. Soft power leaves certain things powered up,
including the NIC and the soft power circuit itself, and to completely shut
down, power needs to be disconnnected. The switch is just a little bit more
elegant than pulling the plug.

 

[JAD]

I'm noticing that all power supplies nowadays seem to have an on/off
switch on the back. My 5-year old Antec doesn't have one. What is the
point of this?

Especially considering that they've now made it so that

you can't turn off a computer by just pressing the power button on the
case,

Wrong....this is a cmos switch on most decent boards(bios)....soft off or
power down....AND if you hold that power button for 4-5 seconds guess what,
it powers off. Turning off the computer without first shutting down windows
is a disaster waiting to happen. So, if your doing this continuously don't
start Bill bashing.




you have to shut down the OS (at least with Windows you do). Now

 

[John Weiss]

I'm noticing that all power supplies nowadays seem to have an on/off
switch on the back. My 5-year old Antec doesn't have one. What is the
point of this?

To be able to remove all power from the motherboard, and still maintain a
ground.

 

[T Shadow]

To be able to remove all power from the motherboard, and still maintain a
ground.

That's a good outcome for the consumer but I doubt it's the reason. Top of
my list is liability. Most people don't know the computer isn't actually
off. It's not too hard to imagine how that would affect a lawsuit.

 

[skotl]

There seems to be a lot of disinformation around this subject.

An ATX power supply may have a switch on the rear panel and, if
present, this is an absolute power on/power off switch. In other words,
if you set the rear switch off then there is no power anywhere.

Most confusion comes from what happens with the on/off switch on an ATX
PSU/Motherboard combination...

In the olden days, the PSU (Power Supply Unit) switch was a 240v /
kill-you-dead switch. Now what happens is that when the PSU has any
power at all, the switch is always being fed a signal. For the techies
amongst you this means that, while the PSU appears to be down it is
still applying power to a handful of rails (Notably VSB on pin 9, of
which more later).
This then allows us (case and computer manufacturers) to add a
low-power on/off switch which is effectively a momentary contact switch
between two connectors on the ATX PSU connector.
The ATX connector has pin 14 designated as PS-ON (Power Supply On) and
when you hit this it connects pin 14 to ground (any of the ground pins
on the ATX PSU connector) and this instructs the power supply to supply
voltage to the main power rails.
In return for this good grace, the PSU expects a *good* signal to be
applied to the PWR_OK line (pin 8) within 0.25 seconds.

The tricky bit in all this is that grounding pin 14 (PS-ON) after the
system has powered up is interpreted as a shutdown signal to the
operating system and it is up to the O/S to begin an orderly shutdown
when it receives this signal.
If the circuitry sees a PS-ON to ground (i.e power off) signal for more
than 4 seconds then it will perform a PSU shutdown.

**Note: The VSB line is intended to provide power for
on/off/standby/restore circuitry

 

[DevilsPGD]

In message <[email protected]> Conor

Tell me, what do you do to turn off your computer if it locks up solid
due to overheating for example?

Me? I reach round the back and hit the switch on the PSU.

Reset button, or press and hold the power button for a few seconds.

 

[Mxsmanic]

I'm noticing that all power supplies nowadays seem to have an on/off
switch on the back.

I don't recall ever seeing a power supply without one, although it
would not surprise me if some low-end models lacked a switch. It
seems a bit unsafe, though.

My 5-year old Antec doesn't have one. What is the
point of this?

It ensures that there is no power at all going into the power supply.
Everything beyond the power plug should be dead when the switch is
turned off.

It's called "fail-safe design."

Especially considering that they've now made it so that
you can't turn off a computer by just pressing the power button on the
case, you have to shut down the OS (at least with Windows you do).

The power isn't actually turned off when you do this, although the
major components of the computer are turned off.

Now all power supplies have an on/off switch, so you can turn off the
computer without shutting down the OS?

Whatever the reason, it's a good idea.

 

[Mxsmanic]

Not all, but many. I can see how this could cause problems if you used it
to turn off a running computer, but I believe the idea is to be able to turn
off the power when the computer is shut down, yet leave it plugged in and
therefore grounded. One would shut down the computer from the OS, then turn
it off at the PSU switch, then hit the power button once to bleed any
charges off the motherboard before opening things up.

Hitting the power button serves no purpose if the main switch has
completely denergized the power supply.

Once upon a time the power switch on the front panel did just this, turn off
the AC to the PSU. Maybe after a few years of soft power switches, people
are beginning to see the virtue of having a hard AC switch available.

I like having actual hardware that turns the power off.

 

[Mxsmanic]

Turning off that switch is just like pulling the power cord, which
usually causes problems with Windows.

NT-based versions of Windows can tolerate it (although not all Windows
_applications_ can tolerate it). However, it's never a good idea to
use the power switch to shut down the system. It _is_ a good idea to
have such a switch, however, since it provides a way of completely
denergizing the system without pulling the power cord.

 

[Mxsmanic]

Reset button, or press and hold the power button for a few seconds.

And if the PSU doesn't feel like recognizing these?

 

[Mxsmanic]

Wrong....this is a cmos switch on most decent boards(bios)....soft off or
power down....AND if you hold that power button for 4-5 seconds guess what,
it powers off.

Unless, of course, there is a problem with the boards that are
supposed to support this switch, in which case you're out of luck
unless you have an actual, physical, real, honest-to-goodness power
switch that really does turn off the power.

Turning off the computer without first shutting down windows
is a disaster waiting to happen.

Not anymore, but it's never a good idea. On Windows 9x and earlier
versions of Windows, it's extremely unwise because it often corrupts
the file system if the computer is actively doing something at the
time the power is cut.

Any well-designed computer system will have a true power switch, one
that turns off all power to everything inside the box.

 

[Mxsmanic]

That's a good outcome for the consumer but I doubt it's the reason.

I think it's exactly the reason. You need to be able to turn
everything off.

Top of my list is liability. Most people don't know the computer
isn't actually off. It's not too hard to imagine how that would
affect a lawsuit.

What sort of lawsuit?

 

[JAD]

And if the PSU doesn't feel like recognizing these?

and if the earth spins out of control
or if the hoover damn breaks
or if we are visited by aliens

 

[JAD]

I don't recall ever seeing a power supply without one, although it
would not surprise me if some low-end models lacked a switch. It
seems a bit unsafe, though.

your kidding right? for YEARS ATX's came without a power switch. They have
dwindled down to a few these days

It ensures that there is no power at all going into the power supply.
Everything beyond the power plug should be dead when the switch is
turned off.

It's called "fail-safe design."

if the user knows anything about it, or remembers to use it. fail safe?
nope