ac phase control triacs

  
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This is an application of what`s known as `random fire` technique for full phase control. The term random iskind ofmisleading. Dimming cannot be effected bytriggering the gateindiscriminately;triggering (firing)must be done synchronised with the line frequency. The line frequency is detected by finding the zero-cross, the point where the line volt
ac phase control triacs - schematic

age is at or near zero, which occurs with each alternation (half-cycle). The Arduino gets zero-crossing pulses from U1`s output at one of its hardware interrupt pins (D2). The delay angle is selectable via two DIP switches. The default is 1 msec and the DIPs add in binary [i. e. delay time = 1msec + 1, 2, or 3 msec more. ] With that, the conduction angle can be set to 158, 135, 112, or 90 degrees [approx. ]. Obviously, more resolution could be had with more switches, and there`s no obstacle as such in doing so, it`s academic enough, but my objective was not somehigh degree of (or seemingly continuous) variability. This is a research project and thesefew well-definedoptions are sufficient. The zero-cross signal is awaited, its occurrence initiates the Interrupt whereupon the DIPs are read and thereby the delay time determined, then shortly the Gate signal pulses after the appropriate delay time and the process repeats. As there`s a snubber across the TRIAC and a snubber for the gate, too, I do intend to try it all outwith a fan. That`s my plan. But I confess that I`m squishy on it right now - preferring to bask in the glow of my present success before plunging into a power factor situation. I have been using "TRIAC", my preference. Should I use Triac when it`s the first word of a sentence and triac otherwise A textbook of mine, "Industrial Solid-State Electronics", uses the latter word form. 26 NOV 2012 The results with a...



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