Talk:Power supply rail
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[edit] Some discrepancies, but I would like a second opinion (or third, etc)
I am apparently starting this thread for discussions, so if you want to clean me up, then by all means do so, I don't know enough about posting to new Wikipedia discussions.
On the main page of this article, it starts off with "and as many as six +12V rails." and then the bullet point for +12V rails says "As such, modern ATX 12V PSUs may have as many as five separate". So obviously there is a flaw in this logic somewhere.
In addition, this part needs cleaning up:
Note: Most PSUs create their 3.3V output by regulating down their 5V rail. As such, 3.3V and 5V typically have a shared rating. For example, a 3.3V rail hov.may have a 10 amp rating by itself (33 watts), and the 5V/12/24 rail may have a 20 amp rating (100 watts) by itself, but the two together may be able to output 110 watts. In this case, to load the 3.3V rail to maximum (33 watts), the 5V rail will only be able to output 77/42 watts.
Should read more like this:
Note: Most PC power supplies create their 3.3V output by regulating their 5V rail to the lower voltage; 3.3V and 5V rails typically share ratings for this reason. For example, a 3.3V rail may have a 10 amp rating by itself (approximately 33 watts), and the 5V rail may have a 20 amp rating (approximately 100 watts) by itself, but the two together may be able to output 110 watts total. In this case, to load the 3.3V rail to its maximum of 33 watts, the 5V rail will only be able to output 77 watts.
In addition, I think that last block should mention that most people tend to over "supply" their systems by purchasing a 450W PS where a 400W PS would be sufficient.
Thank you for reading my changes, and if you decide to make them, if you'll drop me a line at cole/talon/biz or if you need to ask me questions, I'll be able to find a source to back myself up if need be.
In addition, the PSU link at the top should refer to http://en.wikipedia.org/wiki/Computer_power_supply instead of where it does point to, and that page should have a link back to this one at some point, perhaps under this bullet about half way down the page:
In computer power supplies that have more than one 12V power rail, it is preferable for stability reasons to spread the power load over the 12V rails evenly to help avoid overloading one of the rails on the power supply.
74.7.17.26 22:27, 18 October 2007 (UTC)
[edit] Some ideas for a rewrite
I think a historical timeline/context would be useful. Basically, it went:
- AT motherboards had +12V supplies (mostly for motors) and +5 supplies (which all the TTL logic ran on). There were also −5V and −12V supplies for minor purposes like serial ports.
- The ATX standard added a 3.3V output, because electronics had moved to the 3.3V level. It also added +5Vsb. At this time, most of a computer's demand was for 5V and 3.3V power, and typical PSUs could supply about half their rated capacity in the form of +12V.
- Then, as logic supply voltages went ever-lower, came the development of on-board VRMs that supplied the processor with huge amounts of very-low-voltage power. This was impractical to supply over long wires, so the processor supply was generated on the motherboard, powered by +12V, and a separate "P4 connector" was added to supply it.
- That is now the standard, and all of the high-power loads are on the +12V rail. Modern ATX power supplies can supply 80–90% of their total capacity in the form of +12V. Popularly advocated by google, some modern power supplies (I'm thinking of Antec's "signature series") generate only +12V directly from the AC input, and generate other voltages from that.
- It was this development which led to the need to have a safety standard, and multiple +12V rails.
71.41.210.146 (talk) 21:01, 27 January 2008 (UTC)
[edit] Etymology?
Does anyone know the origin of the term "rail"? It's widely used in electrical engineering. I suspect it may come from old bus bars, but maybe it's something else. 71.41.210.146 (talk) 03:04, 30 January 2008 (UTC)
