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Controls Training and Service Manual
116
BASIC OPERATION OF THE TRIAC
To better understand the operation of the triac, we need to look at the movement
of electrons in a special type of material used in electronics. Here we have a
semiconductor material with what is called a depletion region. The depletion
region restricts the flow of electrons to a point.
Depletion Region
Semiconductor
By forcing more electrons in to the depletion region, we can cause an overflow of
these electrons resulting in electron flow that in turn produces current. When we
have current flow, the device is on.
Depletion Region
Semiconductor Showing No Movement of Electrons
If we add a third terminal to this simple device and call it the Gate, we have a basic
triac. By sending electrons to the gate, which is connected to the depletion region,
we create an overflow condition. You can see how this device can be turned on or
off by this process. Now to put this in perspective with AC voltage circuits, this ON
and OFF condition takes place every half cycle. When the AC voltage is removed
from the gate, conduction stops.
GA
Semiconductor Showing Movement of Electrons
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