June 6, 2011
about 2 years ago
A triac is a regenerative component. Once it starts conducting above its latching current (which can be as low as 10mA) it won’t stop, even if base voltage goes to zero. To stop it, either interrupt the current running through it, or bypass it momentarily with a pushbutton to eliminate the potential across its main terminals. Of course if it is passing AC, the potential drops to zero each time a positive AC pulse crosses over to become a negative AC pulse, and vice-versa. The triac stops at that instant, and has to be retriggered.
Gate current does not have to “come from the MT2 side.” So long as the gate potential is either higher or lower than the MT1 terminal, the component will start to conduct.
I’m writing a column about the weirdness of triacs for an upcoming Make magazine.
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