David Bearrow wrote:

> This circuit is an 800W triac dimmer. Uses motorola MBS-4991 bilateral
> switch to provide phase control of the triac. 1 meg pot varies the
> conduction angle of the triac from 0 degrees to about 170 degrees to give
> better than 97% of full power to load at max setting. Conduction angle is
> the same for both half cycles at any given setting of the pot.


The OP wants *reverse* dimming. That is: turn *on* the load at the zero
cross point and turn it *off* at some point during the half wave. It is done
that way to eliminate the hash generated by the fast turn on each 1/2 cycle.
You can't use TRIACs for reverse dimming AFAIK and that makes it a
more complicated and expensive than "normal" dimming.
David...

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David Duffy        Audio Visual Devices P/L
U8, 9-11 Trade St, Cleveland 4163 Australia
Ph: +61 7 38210362   Fax: +61 7 38210281
New Web: www.audiovisualdevices.com.au
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