>R2R to control triac

The oddly true anser is that yes, you can. If you steer a triac with DC
then there is a range where by varying gate current you can vary the
firing angle in the fourth quadrant between 270 and 360 degrees (in theory
between 180 and 360 degrees). I would not recommend this for a series
product however. The why this is so has to do with how the triac is fired
by DC when the polarity is 'wrong' (by gate hot carrier current injection
-- the firing point depends on the relationship between -Vak, Cg'g and Ig
which leads to phase control in ac).

Peter

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