A New Triac Trigger to Optimize Consumer Phase Controls

The phase control methods of regulating ac power to consumer products is quite common. Households contain these circuits in diverse places from wall lamp dimmers to dad's variable speed electric drill and mom's electric blender. Common to all these controls is the triac, semiconductor ac switch, and the associated trigger circuit which provides the ``brains'' of the control. The trigger, or ``brain'', portion of the phase control circuit commonly utilizes a resistor capacitor network which, in combination with a voltage thresholds switch device, provides a time delay between the beginning of each half-cycle and the time the triac is triggered, i.e., shortens the portion of time power is supplied the appliance. This time delay is programmed by the resistor value, lower resistor values allowing the capacitor to charge faster, and reach the voltage threshold faster, which triggers the triac earlier in the half-cycle and applies power to the appliance for a greater portion of the half-cycle.