Computer Power Supply on DC - Page 1
Forum section: electronics / projects

author: sonnytiger
author_rank: Frequent Contributor
timestamp: March 15, 2013, 02:40:06 am
content: So I was thinking of a rather brute force but simple method of making an offline power source for my computer, several lead-acid batteries in series at anywhere between 130-370V according to the specs (100-240VAC 10%). This should work obviously as it rectifies the incoming AC anyway, but I am not sure how the filtering and the PFC at the input would take it, can't find a schematic for the power supply in question (Antec HC 750W) as it is just a fairly disposable consumer item but I am sure it just follows basic circuits for PFC, filtering, SMPS etc. Any ideas how the mentioned circuitry would take the DC?

author: amyk
author_rank: Super Contributor
timestamp: March 15, 2013, 11:30:05 am
content: Not sure about PFC but the input filter coils won't care.Somewhat related video:

author: codeboy2k
author_rank: Super Contributor
timestamp: March 15, 2013, 02:45:53 pm
content: I wasn't sure about the PFC either, so I did a simulation on LTSPICE using the LT3799-1 active PFC LED driver.I just downloaded the LTSpice demo circuit on the Linear page:http://www.linear.com/product/LT3799-1With a AC input, the PF was pretty good at about PF=0.95357With a DC input instead of the AC sine, you get a PF=0.99978This particular controller simulated ok with a DC input. Others may not.On that demo circuit, use F4 to label the V1 source + node as + and the - node as -It's used in the PF calculations below as V(+,-)Add the following spice commands to the demo circuit, run it and view the output in the error log with the CTRL-L keyAfter the run, you can only probe and plot V(+,-) and I(V1). But when you do plot V(+,-) and -I(V1), you can clearly see how the active PFC controller keeps the input current draw closely following the input voltage..options plotwinsize=0.options numdgt=15.save V(+,-) I(V1);Power Factor Calculations.meas start param 5ms.meas end param 10ms.meas P AVG -V(+,-)*I(V1) from start to end.meas Vrms RMS V(+,-) from start to end.meas Irms RMS I(V1) from start to end.meas S param Vrms*Irms.meas PF param P/S.tran 10.1ms

author: sonnytiger
author_rank: Frequent Contributor
timestamp: March 15, 2013, 03:25:40 pm
content: well with those 9 volt batteries it wouldn't run long hahahah but I'd be willing to just try it but I just don't wanna smell the magic smoke on my $120 power supply. If I had some money I wouldn't care but as I have a grand total of $0 right now... $120 is a lot. Anybody know of a typical active PFC circuit? cause I know it would be bad if there were inductors across the input, would result in a short circuit essentially. I suppose another option is to just bypass them. I suppose if I try a low current source like the aforementioned nine volt batteries, I could check for excessive current draw which would tell be if there was a problem..... any thoughts?Unfortunately I have no idea how to use spice, but I am weary of simulators anyway as I have heard they are highly unreliable.

author: ConKbot
author_rank: Super Contributor
timestamp: March 15, 2013, 03:39:51 pm
content: Quote from: sonnytiger on March 15, 2013, 03:25:40 pmI dont have any circuits offhand, but an active PFC circuit generally is generally a bridge rectifier with maybe a small cap on the output, and a boost converter which steps the rectified mains upto ~400VDC to feed the main converter. The controller looks at the incoming voltage wave form and makes the current waveform match. As long as the PFC controller doesnt see the DC freak out and shut down (or keep the boost converter switch on) it should be fine. See if your power supply has a review on hardwaresecrets.com. If it does, you should be able to find out what chips they use and look up datasheets all you want.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: March 15, 2013, 05:35:14 pm
content: http://www.hardwaresecrets.com/article/Antec-High-Current-Gamer-750-W-Power-Supply-Review/1141/1Right hurr if anyone is interested, in depth very nice.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: March 15, 2013, 05:40:56 pm
content: From what i have learned so far looking att his site, the PFC is after rectification so it is DC anyway, though pulsating. Still reading more to see what else comes to the fore-front.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: March 15, 2013, 05:58:02 pm
content: Considering the PFC just tries to match the current waveform to the voltage waveform (resulting in a PF of 1 ideally) the only question i see now that needs answering is what he PFC IC will do when the current already matches the voltage as it will in DC operation. The only response to me that seems reasonable is to just let the current through as it is, I would assume my having the controlling MOSFETs on all the time. Any thoughts?

author: sonnytiger
author_rank: Frequent Contributor
timestamp: March 15, 2013, 06:02:47 pm
content: http://www.hardwaresecrets.com/datasheets/CM6800.pdfThis is the datasheet for the PFC/PWM controller ICAccording to the datasheet, the maximum and minimum PFC duty cycles are 95% and 0% respectively had the maximum been 100 then I would have been reassured that it would work just fine on DC, using thishttp://www.hardwaresecrets.com/fullimage.php?image=5584as a reference, it seems that the IC has the ability to shut off the transistors completely (0% duty cycle) meaning that the current will flow through the Inductor through the diode and into the tank capacity without being redirected through the transistors. Any thoughts?