Set an AT power supply to be always on
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I bought a thrift store Compaq Presario to use its power supply and case for a project. It has a power switch on the back, but the front power switch attaches to the motherboard (which is now in the trash). I need the power to be controlled only by the switch on the back. After looking at AT power supply pin diagrams and experimenting I determined that connecting the PowerGood (Orange) line to the -5v (Grey) line does the trick. Does anyone have any tips or gotchas to share?
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I bought a thrift store Compaq Presario to use its power supply and case for a project. It has a power switch on the back, but the front power switch attaches to the motherboard (which is now in the trash). I need the power to be controlled only by the switch on the back. After looking at AT power supply pin diagrams and experimenting I determined that connecting the PowerGood (Orange) line to the -5v (Grey) line does the trick. Does anyone have any tips or gotchas to share?
Hi PIEBALD,
PIEBALDconsult wrote:
connecting the PowerGood (Orange) line to the -5v (Grey) line does the trick.
that does not sound right at all, in many ways. According to some documents (Google!) the "power good" signal is an output from the power supply, which becomes high to tell the motherboard power is good enough to start up (hence release the /RESET input). If the control line is a pseudo-digital one, it should either be pulled high, or pulled to ground, never negative. Normally I expect you need to connect a SENSE input to the corresponding voltage output (that is 3.3V SENSE to 3.3V; or 5.0V SENSE to 5V on older systems). The sense feedback should occur on the motherboard, as close to the highest load as possible, it is intended to achieve a well regulated voltage at that location, independent of voltage drops along the cables/PCB tracks due to varying currents. In conclusion, maybe you interconnected the right pins, but I doubt the names you mentioned apply; and anyhow, if one of them is a sense line, the connection should be next to the actual load, not right at the power supply. So I suggest you check the documentation again, and possibly throw a multimeter to it, to make sure voltages are what they should be. Regards,
Luc Pattyn [Forum Guidelines] [My Articles]
this months tips: - use PRE tags to preserve formatting when showing multi-line code snippets - before you ask a question here, search CodeProject, then Google
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Hi PIEBALD,
PIEBALDconsult wrote:
connecting the PowerGood (Orange) line to the -5v (Grey) line does the trick.
that does not sound right at all, in many ways. According to some documents (Google!) the "power good" signal is an output from the power supply, which becomes high to tell the motherboard power is good enough to start up (hence release the /RESET input). If the control line is a pseudo-digital one, it should either be pulled high, or pulled to ground, never negative. Normally I expect you need to connect a SENSE input to the corresponding voltage output (that is 3.3V SENSE to 3.3V; or 5.0V SENSE to 5V on older systems). The sense feedback should occur on the motherboard, as close to the highest load as possible, it is intended to achieve a well regulated voltage at that location, independent of voltage drops along the cables/PCB tracks due to varying currents. In conclusion, maybe you interconnected the right pins, but I doubt the names you mentioned apply; and anyhow, if one of them is a sense line, the connection should be next to the actual load, not right at the power supply. So I suggest you check the documentation again, and possibly throw a multimeter to it, to make sure voltages are what they should be. Regards,
Luc Pattyn [Forum Guidelines] [My Articles]
this months tips: - use PRE tags to preserve formatting when showing multi-line code snippets - before you ask a question here, search CodeProject, then Google
I'm discarding the motherboard; I just need the power supply to supply power whenever the switch is on. It's an AT power supply, so no 3.3V lines. I could try connecting the PowerGood to Ground. The resources I've found are: http://home.cogeco.ca/~rpaisley4/ATpsu.html[^] http://pinouts.ru/Power/MotherboardPower_pinout.shtml[^] http://en.wikipedia.org/wiki/Computer_power_supply[^] http://www.directron.com/2powersupplies.html[^]
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I'm discarding the motherboard; I just need the power supply to supply power whenever the switch is on. It's an AT power supply, so no 3.3V lines. I could try connecting the PowerGood to Ground. The resources I've found are: http://home.cogeco.ca/~rpaisley4/ATpsu.html[^] http://pinouts.ru/Power/MotherboardPower_pinout.shtml[^] http://en.wikipedia.org/wiki/Computer_power_supply[^] http://www.directron.com/2powersupplies.html[^]
Hi, the fourth link tells us ATpsu should work without any special wiring. didn't it work for you with PG open? the second link suggests "power good" is an output which goes high when everything has stabilized, as I expected. So connecting it to -5V seems a bad idea. And I trust you read about the minimum load required (around 0.8A). :)
Luc Pattyn [Forum Guidelines] [My Articles]
this months tips: - use PRE tags to preserve formatting when showing multi-line code snippets - before you ask a question here, search CodeProject, then Google
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Hi, the fourth link tells us ATpsu should work without any special wiring. didn't it work for you with PG open? the second link suggests "power good" is an output which goes high when everything has stabilized, as I expected. So connecting it to -5V seems a bad idea. And I trust you read about the minimum load required (around 0.8A). :)
Luc Pattyn [Forum Guidelines] [My Articles]
this months tips: - use PRE tags to preserve formatting when showing multi-line code snippets - before you ask a question here, search CodeProject, then Google
Most sources say that the AT PSU has the front switch connected directly to it, whereas the ATX has the front switch connected to the motherboard; this particular one seems to be an in-between design; newer than AT, older than ATX. I'll mention that it also has another connector for the motherboard with three green and three black wires, which (from what I read) seems to be for PCI cards?
Luc Pattyn wrote:
And I trust you read about the minimum load required (around 0.8A).
I skipped it until I read your earlier response. :-D
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Most sources say that the AT PSU has the front switch connected directly to it, whereas the ATX has the front switch connected to the motherboard; this particular one seems to be an in-between design; newer than AT, older than ATX. I'll mention that it also has another connector for the motherboard with three green and three black wires, which (from what I read) seems to be for PCI cards?
Luc Pattyn wrote:
And I trust you read about the minimum load required (around 0.8A).
I skipped it until I read your earlier response. :-D
It might be a nonstandard design like the dell PSUs from that era, in which case you'll need to track down maker specific data. IIRC the standard (but rarely used) 1x6 extra power cable provided 2 different voltages as well as ground.
-- If you view money as inherently evil, I view it as my duty to assist in making you more virtuous.
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Hi, the fourth link tells us ATpsu should work without any special wiring. didn't it work for you with PG open? the second link suggests "power good" is an output which goes high when everything has stabilized, as I expected. So connecting it to -5V seems a bad idea. And I trust you read about the minimum load required (around 0.8A). :)
Luc Pattyn [Forum Guidelines] [My Articles]
this months tips: - use PRE tags to preserve formatting when showing multi-line code snippets - before you ask a question here, search CodeProject, then Google
I've now connected the -5 to ground and it seems to be working fine. If it goes "poof" I'll let you know. :-D
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I've now connected the -5 to ground and it seems to be working fine. If it goes "poof" I'll let you know. :-D
:confused::confused::confused: Why do you insist on short-circuiting something? the purpose of the -5V output pin is to provide a voltage of -5V with respect to the GROUND pins, and not to be short-circuited. Maybe it will survive your abuse, but it does not have to. And maybe it will solve your problem, but it does not have to either. The only thing you should do is provide some load to the +5V (i.e. between +5V and ground) in such a way that at least 0.8A is flowing all the time. A 5 to 6 ohm resistor should do the trick, but be careful it will heat up and must be strong enough to dissipate 4 to 5W (current*voltage) so it cannot be a regular .25W or .5W resistor, it would have to be one of those wire-wound resistors (about 1 inch long, 1/3 inch thick). Alternatively you could attach a light bulb (as from a bike's or car's head light), that too would (have to) heat up a bit, again dissipating some 5 Watts. What also is supposed to work is just connecting an obsolete motherboard, whatever is on board will need a couple amps. And whatever you do, once everything has been set up, I suggest you actually measure the voltages you plan on using, before you use them, since after your experiments I am not that confident your PSU is still OK... :)
Luc Pattyn [Forum Guidelines] [My Articles]
this months tips: - use PRE tags to preserve formatting when showing multi-line code snippets - before you ask a question here, search CodeProject, then Google