Basic_triac_switches

Published:2009/7/21 22:03:00 Author:Jessie | From:SeekIC

These circuits show triacs that are used to control a pure resistive load (of about 7 A) across an ac line. In Fig. 8-5A, gate current is supplied to the triac from the 10-V battery when S1 is closed. The triac tums on and remains on until S1 is opened. This cirquit switches at zero current, except for initial turn on, so S1 can be a very low-current switch (carring only triac gate current). The triac switch of Fig.8-5B has the same characteristics as Fig. 8-5A, except that the battery is eliminated. In the circuit of Fig. 8-5C, when S1 is in position 1, the triac receives no gate current and is nonconducting. With S1 in position 2, operation is the same as in Fig. 8-5B. With S1 in position 3, the triac receives gate current only on positive half-cycles, and power to the load is half-wave. Figure 8-5D shows ac control of the triac.



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