Power factor correction
in [Design]
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From: Tim Williams on 29 Dec 2009 08:17 PFC is a flyback thing. But flybacks suck over 100W, where forward looks better. But forward sucks over wide duty cycle ranges. What do they do, just bigger flybacks? Nothing at all? Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Jan Panteltje on 29 Dec 2009 08:44 On a sunny day (Tue, 29 Dec 2009 07:17:31 -0600) it happened "Tim Williams" <tmoranwms(a)charter.net> wrote in <Yhn_m.18015$wC3.5829(a)newsfe07.iad>: >PFC is a flyback thing. But flybacks suck over 100W, where forward looks >better. But forward sucks over wide duty cycle ranges. What do they do, >just bigger flybacks? Nothing at all? > >Tim > >-- >Deep Friar: a very philosophical monk. >Website: http://webpages.charter.net/dawill/tmoranwms For much higher power 3 phase rectifiers are used. That leaves only a small ripple. I am not sure if you need PFC in such a case.
From: Phil Allison on 29 Dec 2009 08:57 "Tim Williams" > PFC is a flyback thing. ** Come back when you sober up. Fuckhead. .... Phil
From: MooseFET on 29 Dec 2009 09:41 On Dec 29, 5:17 am, "Tim Williams" <tmoran...(a)charter.net> wrote: > PFC is a flyback thing. But flybacks suck over 100W, where forward looks > better. But forward sucks over wide duty cycle ranges. What do they do, > just bigger flybacks? Nothing at all? At modestly larger that 100W the flyback booster method still works ok. The bulk of the power is transfered by the booster when its boost ratio is small. To handle the very wide duty cycle dropping the frequency as the mains nears its peak works. Multiple boosters running out of phase will let you go up to higher power levels and the ripple tends to cancel. Other designs do use various sorts of forward converters. No matter what you do, you need to have a core somewhere that has a significant energy storage. To make the forward converter method work, the output side inductor has to do the storing. Going up in frequency, keeps the inductor's mechanical size smallish.
From: Hammy on 29 Dec 2009 13:07
On Tue, 29 Dec 2009 07:17:31 -0600, "Tim Williams" <tmoranwms(a)charter.net> wrote: >PFC is a flyback thing. But flybacks suck over 100W, where forward looks >better. But forward sucks over wide duty cycle ranges. What do they do, >just bigger flybacks? Nothing at all? > >Tim They use CCM Boost topology for PFC. See NCP1654 for example. http://www.onsemi.com/PowerSolutions/product.do?id=NCP1654 |