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In Reply to: RE: check out posted by beautox on December 09, 2014 at 00:48:06
"the problem is that the current is drawn in short bursts, rather than uniformly over the whole cycle (non-linear). Caps can't fix this problem. "
I think large caps can reduce the effect from short burst current draw: some of the current is drawn from the cap. But I do not know how a large cap in an external box AC filter can be safe for human beings.
Follow Ups:
I was talking about power factor correction. And caps can't fix this. In fact the caps that follow the diodes in a power supply are what *cause* the power factor problem; the bigger the caps, the worse the power factor (roughly speaking), as the bursts that the AC is higher voltage than the caps (and hence charging them) is shorter.
The bigger the DC caps, the worse the power factor.AC caps, however, can make the power factor better.
Reducing THD in the AC waveform, caused by current surge by AC to DC converters, is also power factor correction in broad sense.
"The capacitance be in parallel AC filter" in my original post was the capacitance of AC capacitor.
Edits: 12/13/14
I maintain that putting caps across the AC line is not really going to affect the power factor a whole lot. Not without an inductor there as well. Sure, a little bit. But as the calculations above have shown, you can't really have a very large cap directly across the AC, ~100uF max thereabouts. This isn't typically going to affect the PF much.
Actually this is something I'd been thinking about for some time : why does nobody make audio gear with active power factor correction? (Correct me if I'm wrong) Passive correction is not very efficient, even when done properly with inductors and capacitors you only normally get up to 0.75 or thereabouts.
Active correction can get you a PF up to almost 1. But as with most engineering, there are tradeoffs, the most significant of which for us audiophiles is the EMI that such switching devices produce. Look up "duel stage active pfc" for example.
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