Triac Applications

Applications of Triac Next to SCR, the triac is the most widely used member of the thyristor family. In fact, in many of control applications, it has replaced SCR by virtue of its bidirectional conductivity. Motor speed regulation, temperature control, illumination control, liquid level control, phase control circuits, power switches etc. are some of its main applications. However, the triac is less versatile than the SCR when turn-off is considered. Because the triac can conduct in either direction, forced commutation by reverse-biasing cannot be employed. So turn-off is either by current starvation, which is usually impracticable, or else by ac line commutation. There are…

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Triac Characteristics

Characteristics of  Triac Typical V-I characteristics of a triac are shown in figure. The triac has on and off state characteristics similar to SCR but now the char acteristic is applicable to both positive and negative voltages. This is expected because triac consists of two SCRs connected in parallel but opposite in direc tions. MT2 is positive with respect to MTX in the first quadrant and it is negative in the third quad rant. As already said in previous blog posts, the gate triggering may occur in any of the following four modes. Quadrant I operation     :     VMT2, positive; VG1…

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Triac-Construction and Operation

Introduction to Triac-Its construction and Operation The triac is another three-terminal ac switch that is triggered into conduction when a low-energy signal is applied to its gate terminal. Unlike the SCR, the triac conducts in either direction when turned on. The triac also differs from the SCR in that either a positive or negative gate signal triggers it into conduction. Thus the triac is a three terminal, four layer bidirectional semiconductor device that controls ac power whereas an SCR controls dc power or forward biased half cycles of ac in a load. Because of its bidirectional conduc­tion property, the triac…

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