ATX Power Supply Unit Notes

Tags: psu, troubleshoot, computer, mb, pins, atx, active pfc

Testing

To test an ATX power supply temporarily, short pins 14 and 15 as shown here:

http://www.duxcw.com/faq/ps/ps4.htm

Do at your own risk!

20 pin vs 24 pin

Technically you can plug a 20 pin into a 24 pin motherboard, but not really, you risk overloading some of the wires.

http://www.smps.us/20-to-24pin-atx.html

Dell Notes

Dimension 2xxx - standard ATX 20 pin PSU + 4 pin supplementary

Vostro 200 - rare size, but sort of standard (BTX?), 24 pin + 4 pin.

Active PFC Notes

Some messy notes on Active PFC.

Active PFC's are not univerally compatible with non-sine wave UPS's, i.e. the cheaper stepped (or worse, square) wave UPSs
DB of UPS models and their output waveform: https://www.hardwareinsights.com/database-of-ups-output-waveforms/
Guy has Dell servers 2011 reboot after very brief outages, but his ups saves machines on longer outages. PCs OK. https://www.dell.com/community/PowerEdge-Hardware-General/power-outage-transfer-time-poweredge-6850-specification/td-p/3685722
Active PFC power supplied (I would think these Dells have them) do not play well w/some UPSs (which we don't have) - but I wonder if Active PFC has less buffer on outages - or perhaps the surge protector on the power bar lopped off the top of a spike and the active PFC ran out of whatever - https://superuser.com/questions/127636/why-pc-reboots-when-there-s-a-power-failure-even-with-ups
I'm Thinking this is what happened. https://superuser.com/questions/912679/when-do-i-need-a-pure-sine-wave-ups/912749#912749
"These new power supplies can detect fluctuation of 3ms" https://serverfault.com/questions/199861/ups-with-a-hp-proliant-server
https://electronics.stackexchange.com/questions/22083/how-does-active-power-factor-correction-in-computer-power-supplies-work
http://www.embedinc.com/pfc/ - "The PFC part is performed by a boost converter taking the raw rectified AC line as input. The boost converter switches at many times the power line frequency such that the power line voltage changes relatively little between each boost pulse. The boost converter produces a voltage somewhat higher than the highest peak of the AC input line. For each boost pulse, the average current drawn from the AC line for that pulse interval is proportional to the instantaneous AC line voltage. The current drawn from the AC line is therefore sinusoidal and in phase with the voltage. In other words, the load on the AC line appears resistive, which is the ideal case. " (Is this like a joule thief circuit?)