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From: jans@mako.UUCP (Jan Steinman)
Newsgroups: net.ham-radio
Subject: Re: light dimmers (and RFI, a solution for HW types)
Message-ID: <568@mako.UUCP>
Date: Fri, 1-Feb-85 13:14:40 EST
Article-I.D.: mako.568
Posted: Fri Feb  1 13:14:40 1985
Date-Received: Sun, 3-Feb-85 11:09:51 EST
References: <192@lcuxc.UUCP>
Reply-To: jans@mako.UUCP (Jan Steinman)
Distribution: na
Organization: Tektronix, Wilsonville OR
Lines: 19

In article <192@lcuxc.UUCP> wjm@lcuxc.UUCP (B. Mitchell) writes:
>The problem is that the SCR or triac does the dimming by "chopping" the AC
>sine wave part  way through the cycle.

I once designed a dimmer based upon zero-switching and digital cycle-counting.
To dim the light to 40%, only allow 40 out of 100 half-cycles to pass.  This
method is easier on the triac and lamp, but takes more hardware and won't
really fit in an outlet box.  A side advantage is that it is more easily
interfaced to a computer than the phase-control technique.  A more serious
problem is that there is excessive flicker at very low duty cycles -- at 2%
light, a cycle is passed about once a second!  Practical experience showed
levels as low as 10% (6 Hz flicker rate) were tolerable, (due to filiment,
not visual, persistance) with the typical useage range of 30% - 70% working
quite well.

Best of all, absolutely no RFI!
-- 
:::::: Jan Steinman		Box 1000, MS 61-161	(w)503/685-2843 ::::::
:::::: tektronix!tekecs!jans	Wilsonville, OR 97070	(h)503/657-7703 ::::::