Sound to Light

The diagrams below are to illustrate how the triac is used to vary the brightness of the light bulb. The first diagram represents a graph of voltage against time for the 220v supply.

The next two diagrams represent graphs of current flowing through the triac (and light bulb) against time. In these diagrams, t1 is the time at which the monostable is triggered and t2 is the time (a few milli-seconds later) when it reaches the end of its timed period and gives a pulse to start the triac conducting.

N.B. when the current through a triac falls to zero, it returns to its non-conducting state until it receives another pulse into its gate.

Light at about half power

Light at less than half power