Triac Protection
Triac Protection
Thyristors
Damage can occur to a thyristor if the thyristor’s repetitive peak off-state voltage is
exceeded. A thyristor’s repetitive peak off-state voltage may be exceeded due to dirty AC
power mains, inductive spikes, motor latch up, and so on.
Thyristor Reference Circuit
Figure 3.40 and Figure 3.41 show two different methods of protecting a triac. In Figure 3.40,
a SIDACtor device is connected from MT2 to the gate of the triac. When the voltage applied
to the triac exceeds the SIDACtor device’s VDRM, the SIDACtor device turns on, producing a
gate current which turns the triac on.
Hot
Load
47 Ω
MT2
MT1
Triac
SIDACtor
To
Gating
Circuitry
Neutral
Figure 3.40 TRIAC Protection
The circuit in Figure 3.41 places a SIDACtor device across MT2 and MT1 of the triac. In this
instance the SIDACtor device protects the triac by turning on and shunting the transient
before it exceeds the VDRM rating of the triac.
Hot
Load
MT2
MT1
Triac
SIDACtor
To
Gating
Circuitry
Neutral
Figure 3.41 TRIAC Protection
With both methods, consider the following designs when using a SIDACtor device to protect
a thyristor:
•
•
•
VDRM of the SIDACtor device < VDRM of Triac
SIDACtor device VDRM > 120% VPK(power supply)
SIDACtor device must be placed behind the load
© 2002 Teccor Electronics
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+1 972-580-7777
®
SIDACtor Data Book and Design Guide
TECCOR [ TECCOR ELECTRONICS ]
