The triac is an element of an electronic device designed to control the flow of alternating current. The name of this item comes from the English combination (trade name) TRIAC – triode for alternating current. Formally speaking, this element, sometimes referred to as symistorem, type thyristor. Triaki used to control alternating current in the power systems, and power management in devices using alternating current to power the chains of power, for example, in systems with electric heaters.
Triaki are a subset of thyristors. Differ from them in that provide current flow in both directions, while a thyristor can conduct current only in one direction. Most elements of this type may start in goal against the positive or negative voltage (of a thyristor requires a positive voltage). After his release, both elements behave in the same way – remain open even if the current goal terminated as long as the current flowing through the system does not fall below a certain level called holding current.
Triac, consisting of four PNPN semiconductor layers. The extreme layers of this element form an output current, called anodami, between which flows the operating current of the system. From the inner layer is the output control, that is, the base. After submission to base a positive or negative voltage, the system begins to between anodami. Even after disconnecting the voltage from the base, between anodami triaka will flow current. Just at the moment when the voltage between anodami falls below a certain threshold, the current will stop.
Dwukierunkowość triaków makes them convenient switches for alternating current. In addition, the use of the trigger at a controlled phase angle of the current in the circuit, provides control of the average current supplied to the load (phase control). It is widely used for motor speed control AC in ściemniaczach that to control electric radiators. These systems are very simple and consist only of a detector voltage passes through zero and the driver triaka.