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From: ftpam1@acad3.fai.alaska.edu (MUNTS PHILLIP A)
Newsgroups: sci.electronics
Subject: Re: Light Dimmer
Message-ID: <1990Nov24.205337.18959@hayes.ims.alaska.edu>
Date: 24 Nov 90 20:53:37 GMT
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In article <2570007@hppad.HP.COM>, lindner@hppad.HP.COM (Steffen Lindner) writes...
>I would appreciate it if any of you could help me with the following:
> 
>Background Information:
>I am trying to built a digitally controlled light dimmer.  This system should
>control about 24 individual channels.  Each channel consists of one or more
>lights (incandescent).  The maximum load on each channel is about 3A.  The
>dimmer must allow a minimum of 16 brightness settings (more would be better).
>The system uses a microcontroller for I/O and triggering the TRIACs.  All
>seems well except that I have not been able to come up with a simple, cost
>effective solution to reduce (eliminate) noise.
> 
>Problem:
>A regular dimmer setup (controlling the phase angle of a TRIAC) produces 
>substantial current spikes, since the load current is turned on under
>non-cross-over conditions.  This causes a lot of interference.         
> 
>Another solution would be to always switch at cross-over points and just skip
>one or more half cycle.  This works well as long as not too many cycles
>are skipped.  At 1/16 of full brightness there would be a substantial flicker
>noticable.
> 
> 
>Are there any better methods of building a dimmer?  
>Is there any way to trigger the TRIAC "gently" (ie. soft start)?
> 
> 
>				Please help,             
> 
>				   Steffen       

     I once had occasion to replace the SCR's in a commercial stage light
controller.  That particular system had toroids (inductors) larger than glazed
donuts.  I don't remember what the associated capacitors were; the coils were
so large that they monopolized your attention!

(This system was rated at 2.4 kW per channel.  Each channel had its own LC
noise filter.)

Philip Munts N7AHL
NRA Extremist, etc.
University of Alaska, Fairbanks