A TRIAC is a three-terminal electronic component that conducts current in either direction when triggered. It is a subset of thyristors and is related to silicon controlled rectifiers (SCRs). TRIACs differ from SCRs in that they allow current flow in both directions, whereas an SCR can only conduct current in a single direction. Most TRIACs can be triggered by applying either a positive or negative voltage to the gate (an SCR requires a positive voltage). The bidirectionality of TRIACs makes them convenient switches for alternating-current (AC) and they are commonly used for controlling the speed of a universal motor, dimming lamps, and controlling electric heaters. TRIACs are bipolar devices and can handle a wide range of current and voltage. They are versatile because of their ability to operate with positive or negative voltages across their terminals. TRIACs are often used in low to medium power AC switching requirements. They are also used in many other power control situations including motor control and electronic switches.