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From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: Fluorescent light ballasts
Summary: Many different fluorescent lamp circuits...
Keywords: advance
Message-ID: <3507@kitty.UUCP>
Date: 19 Nov 89 03:42:12 GMT
Article-I.D.: kitty.3507
References: <22334@gryphon.COM> <4995@ae.sei.cmu.edu> <3504@kitty.UUCP> <596@nikhefk.UUCP>
Organization: Recognition Research Corp., Clarence, NY
Lines: 32

In article <596@nikhefk.UUCP>, henkp@nikhefk.UUCP (Henk Peek) writes:
> >	The primary purpose of a ballast is for current limiting, and it
> >therefore functions as a saturable inductor and not a transformer.
>
> A ballast inductor operates always in the non sataurable mode.
> When the iron saturates the inductance of the inductor goes very fast down
> and the current goes up.

	Not true where there is a capacitor and hence a resonant circuit
involved, a design which is commonly found in fluorescent lamp circuits
which employ no starter.

	In addition, some types of fluorescent lamp circuits employ a dual
inductor with intentional magnetic field coupling.  Such a device is usually
called a "stray-field" or "leakage-reactance" transformer, although its
characteristics are different from that of a conventional transformer so
that current limiting can be provided.  In a conventional transformer the
mutual magnetic field which links both windings must be kept as high as
possible in order to transfer the maximun energy.  A stray-field transformer
has reduced mutual magnetic flux, resulting in limited energy transfer.  As
increased load is drawn leakage flux increases and output voltage drops.
A stray-field transformer in fluorescent lamp applications usually has
common primary and secondary connections as in an autotransformer, and is
also viewed by some as being two series inductors.

	Fluorescent lamp ballast circuits are more complex than one would
imagine.

<> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp.
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