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Diac vs Triac | Difference between Diac and Triac

This page Diac vs Triac describes difference between Diac and Triac.It explains basics of Diac and Triac and mentions useful difference between terms.



As we know, thyristor is a half wave device similar to the diode and hence will provide only half power. A Triac device consists of two thyristors connected in parallel but in opposite directions and is controlled by the same gate.

Triac is a two dimentional thyristor which is triggered on both halves of the input a.c. cycle using positive or negative gate pulses. Triac connecting terminals are MT1, MT2 and gate(G) as shown. The triggering pulses are applied between G and MT1 terminals. The gate current to handle 100A from triac is not more than 50mA or so.



Diac is made of two zener diodes connected back to back. One of the application of these devices is shown in the figure-3 as lamp dimmer circuit. It conducts in either direction when the voltage across C1 reaches it breakdown value of approx. 30 volt. A current pulse fom C1 triggers the triac and power is supplied to the load (here lamp). The conducting period of triac depends on value R1. The more is the value of R1, C1 will get charged very slowly. This makes triac turn on very late in the cycle and hence light will be more dim.

lamp dimmer using diac and triac

After the study of Diac and Triac, one can also refer various electronic terminologies as well as difference between Diac, triac with SCR and UJT as mentioned below.

Difference between SCR, Diac, Triac, UJT and junction Transistor

Refer Difference between SCR,DIAC,TRIAC,UJT➤➤ with respect to structure, circuit symbol and characteristics.


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