From: John Woodgate
Subject: Re: Power Factor Correction
Date: Tue, 24 Sep 2002 22:03:36 +0100
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Tue, 24 Sep 2002 21:58:36 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Stefan Toftevall wrote (in ) about
'Power Factor Correction', on Tue, 24 Sep 2002:
>How is PFC implemented into a full-bridge / half-bridge SMPS?
>I know what PFC is, the current draw of the supply must be in phase with the
>In normal ways, the mains is input to a rectifier and then directly to the
>The goverment here in Sweden demands that smps-design beyond 50W must have
Are you sure? People misinterpret EN61000-3-2 to mean that, but it
>I'm designing a half-bridge supply of 1kW.
What is it for? If it's for 'professional equipment', as defined in EN
61000-3-2, you may not need to put in PFC.
The sort of PFC you need for a SMPS is different, and a lot more
complicated, than that for a simple inductive load, such as a
fluorescent lamp with inductive ballast. For that, you only need a
capacitor to reduce the lagging current.
The SMPS draws current from the mains in short pulses, lasting from one-
sixth to one-quarter of a cycle. This current contains lots of harmonics
of the supply frequency, which can cause problems in the mains supply
network and to other loads connected to it.
To make the current more nearly sinusoidal, you have to force the
rectifier diodes into conduction for nearly a half-cycle by preceding
them with a boost converter.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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