Triac

A triac is an electronic component equivalent to two silicon controlled rectifiers joined end to end or back to back with their gates connected together. This results in a two-directional electronic switch which can conduct current in both directions when it is triggered (turned on). It can be triggered by either a positive or a negative voltage. The device turns off again when the current through it drops below a certain threshold value, such as the end of a half-cycle of alternating current. This makes the triac a convenient switch for AC circuits. Applying a trigger pulse at a controllable point in an AC cycle allows one to control the percentage of current that flows through the triac. Lower power triacs are used in lots of applications, especially domestic electrical appliances, such as light dimmers.