Date: Sun, 12 Sep 1999 01:58:17 -0500 (CDT) From: Kevin Day <toasty@dragondata.com> To: mike@smith.net.au (Mike Smith) Cc: chuckr@picnic.mat.net (Chuck Robey), mike@smith.net.au (Mike Smith), luigi@labinfo.iet.unipi.it (Luigi Rizzo), hackers@FreeBSD.ORG Subject: Re: damn ATX power supplies... Message-ID: <199909120658.BAA43940@celery.dragondata.com> In-Reply-To: <199909120643.XAA00669@dingo.cdrom.com> from "Mike Smith" at Sep 11, 1999 11:43:04 PM
next in thread | previous in thread | raw e-mail | index | archive | help
> > > You can always hotwire the supply; go dig up a pinout for the ATX power > > > connector and you'll see that if you ground the power-on line the PSU > > > will come up... > > > > It's not just a ground, the line that brings up the power is a momentary > > switch, so a longish (about 1/2 second) pulse would do it. That would > > The switch is not connected to the power enable line to the ATX power > supply; it's connected to logic on the system board which in turn (in > some cases) drives the PE line. If you ground the power enable line for > 1/2 a second, you will get (at most) 1/2 a second of power. > > Sheesh. You could at least speak from _experience_ here. > Yeah, you're supposed to tie PE low when you want power... However, in a system I'm working with now, we've discovered that some inexpensive ATX power supplies don't expect to have PE come up immediately when they're given power. If you see the symptom that all the LED's on your system dim about 1-2 seconds after you give the power supply AC for a second or so, you need to make a small timer circuit to wait 5 seconds or so before turning the PE line on. For those that are interested, the issue is that the 5V standby power system in the supply needs time to stabilize, and let some caps charge. +5SB is also used for the power enable circuit. The AC gets turned on, and +5SB comes up. This immediately activates the rest of the power supply, since you've tied PE down. However, since +5SB's caps aren't charged, the huge load from the hard drives and motherboard starting up drain things, and it can't keep the voltage high enough for the PE circuit to remain on. Most supplies aren't made like this, but a few do have this problem. If someone needs a schematic, i could probably come up with a quick and dirty 555 timer system. Kevin To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199909120658.BAA43940>