Useing AT switcher as bench supply.

[Scott Wiper]

Their is a white wire that is labelled power good.

I would like to trick this supply into thinking it is fully on with out
useing a 1R 50watt resistor on the five volt line so I could just use the 12
volts with the switcher going into shut down. I have modded one with molex
connectors on the back for inserting power clips and banana plugs for my
solderless board.

If I take the power good to ground will this work like a ATX switcher where
the green is is taken to ground for PS_ON?

 

[Tim]

You do realize that switching psu tend to explode if they are left
without loads on the outputs, right?

- Tim -

 

[Gregg]

Behold, Tim signalled from keyed 4-1000A filament:

You do realize that switching psu tend to explode if they are left
without loads on the outputs, right?

- Tim -

Eh?

I've been using an XT switcher for a 12V/5V bench supply for years :-/

 

[repatch]

On most supplies you need the resistor, it's there for loading, not for
turning on the supply. A switcher of that type needs a load to function
properly, leaving it out will likely result in the switcher not turning
on, or turning itself off. Some will even be damaged. TTYL

 

[repatch]

While theoretically true, almost all PC power supplies will not "explode",
and to say so is fear mongering, at best.

Most PC power supplies will simply shut down (or not start up). Some
better supplies have internal loading so that no external load is required.

I usually plug in an old hard drive as a load, has worked every time. TTYL

 

[Darrell Larose]

You do realize that switching psu tend to explode if they are left
without loads on the outputs, right?

- Tim -

Damn, you told him! We wanted to see if we could get an Ottawan winning the
Darwin Awards

 

[Scott Wiper]

AFAIK Power good on an AT supply is an output to tell the Mboard that the
power supply is stable, not an input. If you have no output it is because
there is no load probably.

You need to google.

I will google this one out. AT switchers need a load connected to them ATX
switchers will switch on when there when a load is detected. I think is to
prevent output caps from bursting.

I will use a old poor quailty ATX switcher with a SPST switch a 1K resistor
and a green LED to ground for power on. I also Modded that one with molex
connectors. I put the extra wires out for that.

 

[Mjolinor]

Their is a white wire that is labelled power good.

I would like to trick this supply into thinking it is fully on with out
useing a 1R 50watt resistor on the five volt line so I could just use the 12
volts with the switcher going into shut down. I have modded one with molex
connectors on the back for inserting power clips and banana plugs for my
solderless board.

If I take the power good to ground will this work like a ATX switcher where
the green is is taken to ground for PS_ON?

AFAIK Power good on an AT supply is an output to tell the Mboard that the
power supply is stable, not an input. If you have no output it is because
there is no load probably.

You need to google.

 

[Watson A.Name \Watt Sun - the Dark Remover\]

You do realize that switching psu tend to explode if they are left
without loads on the outputs, right?

- Tim -

I've seen electrolytic caps explode when subjected to overvoltage.

But power supplies for PCs, for as long as I can remember, have had
overvoltage shutdown that prevents them from doing anything except shut
down.

 

[Tim]

I have the scars to prove it. Some switching psu will take off with no
load, and the freq will exceed spec and bang! they go ballistic.

Been there, done that.

 

[repatch]

Then it was a VERY poor design and it's scary it was ever in a PC. I can't
believe it would have passed the safety standards in most countries. TTYL

 

[[email protected]]

I have the scars to prove it. Some switching psu will take off with no
load, and the freq will exceed spec and bang! they go ballistic.

Been there, done that.

A common switcher CAN do this, but a CSA approved, or UL approved in
the US of A computer power supply MUST protect itself from this. They
all have overvoltage and over current shut-down..
One thing that makes them kinda nice for bench supplies.

 

[Watson A.Name \Watt Sun - the Dark Remover\]

I have the scars to prove it. Some switching psu will take off with
no load, and the freq will exceed spec and bang! they go ballistic.

Been there, done that.

I've seen 12V equipment lift off the bench when connected to a 28VDC
power supply; so yeah, those electrolytic caps can be quite destructive
when they let go. I've also seen the insides of equipment afterwards,
where the shreds of the 'lytic are stuck all over the rest of the
components on the PC board. So I can relate to the shrapnel that you've
experienced. But all the PSes that I've seen have a crowbar OVP circuit
that just shorts the output to ground with a SCR when the overvoltage is
encountered.

While theoretically true, almost all PC power supplies will not
"explode", and to say so is fear mongering, at best.
Most PC power supplies will simply shut down (or not start up).
Some better supplies have internal loading so that no external load
is required.
I usually plug in an old hard drive as a load, has worked every
time. TTYL

You do realize that switching psu tend to explode if they are
left without loads on the outputs, right?
- Tim -

 

[Tom Del Rosso]

On most supplies you need the resistor, it's there for loading, not
for turning on the supply. A switcher of that type needs a load to
function properly, leaving it out will likely result in the switcher
not turning
on, or turning itself off. Some will even be damaged. TTYL

Or (just to add another to the list of possibilities) it just won't
regulate accurately. That could also affect regulation of the 12V
output.