AN1001
Application Notes
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AN1001 - 2
2002 Teccor Electronics
Thyristor Product Catalog
Triac
Basic Operation
Figure AN1001.4 shows the simple block construction of a triac.
Its primary function is to control power bilaterally in an AC circuit.
Figure AN1001.4
Triac Block Construction
Operation of a triac can be related to two SCRs connected in par-
allel in opposite directions as shown in Figure AN1001.5.
Although the gates are shown separately for each SCR, a triac
has a single gate and can be triggered by either polarity.
Figure AN1001.5
SCRs Connected as a Triac
Since a triac operates in both directions, it behaves essentially
the same in either direction as an SCR would behave in the for-
ward direction (blocking or operating).
Geometric Construction
Figure AN1001.6 show simplified cross-sectional views of a triac
chip in various gating quadrants and blocking modes.
Figure AN1001.6
Simplified Cross-sectional of Triac Chip
N
N
N
P
N
P
Block Construction
Main
Terminal 2
(MT2)
Gate
Schematic Symbol
MT1
Gate
MT2
Main
Terminal 1
(MT1)
MT1
MT2
N
N
N
N
N
N
P
P
P
P
GATE(+)
IGT
MT1(-)
N
N
IT
MT2(+)
QUADRANT I
GATE(-)
IGT
MT1(-)
MT2(+)
QUADRANT II
Blocking
Junction
MT2(+)
MT1(-)
Equivalent Diode
Relationship
N
N
N
N
N
N
N
N
P
P
P
P
GATE(+)
IGT
MT1(+)
IGT
QUADRANT III
GATE(-)
MT1(+)
MT2(-)
QUADRANT IV
Blocking
Junction
Equivalent Diode
Relationship
IT
IT
MT1(+)
MT2(-)
MT2(-)