From: John Woodgate
Subject: Re: Power Factor Correction
Date: Thu, 26 Sep 2002 20:15:36 +0100
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Thu, 26 Sep 2002 22:22:25 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that N. Thornton
wrote (in ) about
'Power Factor Correction', on Thu, 26 Sep 2002:
>Decades ago the usual approach was to put a choke in series with the
>bridge rectifier (on the ac side): would this be a simple way to
>greatly improve the pf? I would think so.
Or on the d.c. side, AAMOF, although the effects are somewhat different.
Yes, this works, but the choke is almost always larger, heavier and more
costly than you can accept. The electronic PFC may not always be
cheaper, but it's always smaller and lighter.
At 25 W, which IIRC the OP wanted, you could simply add resistance in
series with the a.c. side of the bridge rectifier. You lose around 3 W
IIRC, which is not too dreadful. The reduction in inrush current and in
peak diode current both aid reliability.
What you do is to look at the rectifier diode current waveform and
adjust the resistance to get a conduction angle of more than 65 degrees,
if you want to meet the Class D limits (or those Class C limits that are
the same as the Class D limits). If you also look at the harmonic
spectrum (FFT on the diode current), it is instructive to see how the
harmonic amplitudes vary with conduction angle - very NON-monotonic.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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