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From: lindner@hppad.HP.COM (Steffen Lindner)
Newsgroups: sci.electronics
Subject: Light Dimmer
Message-ID: <2570007@hppad.HP.COM>
Date: 23 Nov 90 17:11:21 GMT
Organization: HP Panacom Automation Div Waterloo, Ont.
Lines: 29

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