Silicon control rectifier SCR, also known as thyristor, are divided into two types: unidirectional thyristor and bidirectional thyristor. The Bidirectional SCR are also called triac. The bi-directional SCR or triac is structurally equivalent to two unidirectional SCRs connected in reverse, and the triac has a bi-directional conduction function. Small and medium power SCRs are often used in consumer kitchen appliances, beauty salon tools, household appliances, etc.; High-power SCRs are often used in industrial control, motor speed control, inverters, automatic control circuits, electronic switches, frequency control, etc..